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-rw-r--r--library/std/src/sync/mpsc/blocking.rs82
-rw-r--r--library/std/src/sync/mpsc/cache_aligned.rs25
-rw-r--r--library/std/src/sync/mpsc/mod.rs1669
-rw-r--r--library/std/src/sync/mpsc/mpsc_queue.rs117
-rw-r--r--library/std/src/sync/mpsc/mpsc_queue/tests.rs47
-rw-r--r--library/std/src/sync/mpsc/oneshot.rs315
-rw-r--r--library/std/src/sync/mpsc/shared.rs501
-rw-r--r--library/std/src/sync/mpsc/spsc_queue.rs236
-rw-r--r--library/std/src/sync/mpsc/spsc_queue/tests.rs101
-rw-r--r--library/std/src/sync/mpsc/stream.rs457
-rw-r--r--library/std/src/sync/mpsc/sync.rs495
-rw-r--r--library/std/src/sync/mpsc/sync_tests.rs647
-rw-r--r--library/std/src/sync/mpsc/tests.rs706
13 files changed, 5398 insertions, 0 deletions
diff --git a/library/std/src/sync/mpsc/blocking.rs b/library/std/src/sync/mpsc/blocking.rs
new file mode 100644
index 000000000..021df7b09
--- /dev/null
+++ b/library/std/src/sync/mpsc/blocking.rs
@@ -0,0 +1,82 @@
+//! Generic support for building blocking abstractions.
+
+use crate::sync::atomic::{AtomicBool, Ordering};
+use crate::sync::Arc;
+use crate::thread::{self, Thread};
+use crate::time::Instant;
+
+struct Inner {
+ thread: Thread,
+ woken: AtomicBool,
+}
+
+unsafe impl Send for Inner {}
+unsafe impl Sync for Inner {}
+
+#[derive(Clone)]
+pub struct SignalToken {
+ inner: Arc<Inner>,
+}
+
+pub struct WaitToken {
+ inner: Arc<Inner>,
+}
+
+impl !Send for WaitToken {}
+
+impl !Sync for WaitToken {}
+
+pub fn tokens() -> (WaitToken, SignalToken) {
+ let inner = Arc::new(Inner { thread: thread::current(), woken: AtomicBool::new(false) });
+ let wait_token = WaitToken { inner: inner.clone() };
+ let signal_token = SignalToken { inner };
+ (wait_token, signal_token)
+}
+
+impl SignalToken {
+ pub fn signal(&self) -> bool {
+ let wake = self
+ .inner
+ .woken
+ .compare_exchange(false, true, Ordering::SeqCst, Ordering::SeqCst)
+ .is_ok();
+ if wake {
+ self.inner.thread.unpark();
+ }
+ wake
+ }
+
+ /// Converts to an unsafe raw pointer. Useful for storing in a pipe's state
+ /// flag.
+ #[inline]
+ pub unsafe fn to_raw(self) -> *mut u8 {
+ Arc::into_raw(self.inner) as *mut u8
+ }
+
+ /// Converts from an unsafe raw pointer. Useful for retrieving a pipe's state
+ /// flag.
+ #[inline]
+ pub unsafe fn from_raw(signal_ptr: *mut u8) -> SignalToken {
+ SignalToken { inner: Arc::from_raw(signal_ptr as *mut Inner) }
+ }
+}
+
+impl WaitToken {
+ pub fn wait(self) {
+ while !self.inner.woken.load(Ordering::SeqCst) {
+ thread::park()
+ }
+ }
+
+ /// Returns `true` if we wake up normally.
+ pub fn wait_max_until(self, end: Instant) -> bool {
+ while !self.inner.woken.load(Ordering::SeqCst) {
+ let now = Instant::now();
+ if now >= end {
+ return false;
+ }
+ thread::park_timeout(end - now)
+ }
+ true
+ }
+}
diff --git a/library/std/src/sync/mpsc/cache_aligned.rs b/library/std/src/sync/mpsc/cache_aligned.rs
new file mode 100644
index 000000000..9197f0d6e
--- /dev/null
+++ b/library/std/src/sync/mpsc/cache_aligned.rs
@@ -0,0 +1,25 @@
+use crate::ops::{Deref, DerefMut};
+
+#[derive(Copy, Clone, Default, PartialEq, Eq, PartialOrd, Ord, Hash)]
+#[cfg_attr(target_arch = "aarch64", repr(align(128)))]
+#[cfg_attr(not(target_arch = "aarch64"), repr(align(64)))]
+pub(super) struct CacheAligned<T>(pub T);
+
+impl<T> Deref for CacheAligned<T> {
+ type Target = T;
+ fn deref(&self) -> &Self::Target {
+ &self.0
+ }
+}
+
+impl<T> DerefMut for CacheAligned<T> {
+ fn deref_mut(&mut self) -> &mut Self::Target {
+ &mut self.0
+ }
+}
+
+impl<T> CacheAligned<T> {
+ pub(super) fn new(t: T) -> Self {
+ CacheAligned(t)
+ }
+}
diff --git a/library/std/src/sync/mpsc/mod.rs b/library/std/src/sync/mpsc/mod.rs
new file mode 100644
index 000000000..e85a87239
--- /dev/null
+++ b/library/std/src/sync/mpsc/mod.rs
@@ -0,0 +1,1669 @@
+//! Multi-producer, single-consumer FIFO queue communication primitives.
+//!
+//! This module provides message-based communication over channels, concretely
+//! defined among three types:
+//!
+//! * [`Sender`]
+//! * [`SyncSender`]
+//! * [`Receiver`]
+//!
+//! A [`Sender`] or [`SyncSender`] is used to send data to a [`Receiver`]. Both
+//! senders are clone-able (multi-producer) such that many threads can send
+//! simultaneously to one receiver (single-consumer).
+//!
+//! These channels come in two flavors:
+//!
+//! 1. An asynchronous, infinitely buffered channel. The [`channel`] function
+//! will return a `(Sender, Receiver)` tuple where all sends will be
+//! **asynchronous** (they never block). The channel conceptually has an
+//! infinite buffer.
+//!
+//! 2. A synchronous, bounded channel. The [`sync_channel`] function will
+//! return a `(SyncSender, Receiver)` tuple where the storage for pending
+//! messages is a pre-allocated buffer of a fixed size. All sends will be
+//! **synchronous** by blocking until there is buffer space available. Note
+//! that a bound of 0 is allowed, causing the channel to become a "rendezvous"
+//! channel where each sender atomically hands off a message to a receiver.
+//!
+//! [`send`]: Sender::send
+//!
+//! ## Disconnection
+//!
+//! The send and receive operations on channels will all return a [`Result`]
+//! indicating whether the operation succeeded or not. An unsuccessful operation
+//! is normally indicative of the other half of a channel having "hung up" by
+//! being dropped in its corresponding thread.
+//!
+//! Once half of a channel has been deallocated, most operations can no longer
+//! continue to make progress, so [`Err`] will be returned. Many applications
+//! will continue to [`unwrap`] the results returned from this module,
+//! instigating a propagation of failure among threads if one unexpectedly dies.
+//!
+//! [`unwrap`]: Result::unwrap
+//!
+//! # Examples
+//!
+//! Simple usage:
+//!
+//! ```
+//! use std::thread;
+//! use std::sync::mpsc::channel;
+//!
+//! // Create a simple streaming channel
+//! let (tx, rx) = channel();
+//! thread::spawn(move|| {
+//! tx.send(10).unwrap();
+//! });
+//! assert_eq!(rx.recv().unwrap(), 10);
+//! ```
+//!
+//! Shared usage:
+//!
+//! ```
+//! use std::thread;
+//! use std::sync::mpsc::channel;
+//!
+//! // Create a shared channel that can be sent along from many threads
+//! // where tx is the sending half (tx for transmission), and rx is the receiving
+//! // half (rx for receiving).
+//! let (tx, rx) = channel();
+//! for i in 0..10 {
+//! let tx = tx.clone();
+//! thread::spawn(move|| {
+//! tx.send(i).unwrap();
+//! });
+//! }
+//!
+//! for _ in 0..10 {
+//! let j = rx.recv().unwrap();
+//! assert!(0 <= j && j < 10);
+//! }
+//! ```
+//!
+//! Propagating panics:
+//!
+//! ```
+//! use std::sync::mpsc::channel;
+//!
+//! // The call to recv() will return an error because the channel has already
+//! // hung up (or been deallocated)
+//! let (tx, rx) = channel::<i32>();
+//! drop(tx);
+//! assert!(rx.recv().is_err());
+//! ```
+//!
+//! Synchronous channels:
+//!
+//! ```
+//! use std::thread;
+//! use std::sync::mpsc::sync_channel;
+//!
+//! let (tx, rx) = sync_channel::<i32>(0);
+//! thread::spawn(move|| {
+//! // This will wait for the parent thread to start receiving
+//! tx.send(53).unwrap();
+//! });
+//! rx.recv().unwrap();
+//! ```
+//!
+//! Unbounded receive loop:
+//!
+//! ```
+//! use std::sync::mpsc::sync_channel;
+//! use std::thread;
+//!
+//! let (tx, rx) = sync_channel(3);
+//!
+//! for _ in 0..3 {
+//! // It would be the same without thread and clone here
+//! // since there will still be one `tx` left.
+//! let tx = tx.clone();
+//! // cloned tx dropped within thread
+//! thread::spawn(move || tx.send("ok").unwrap());
+//! }
+//!
+//! // Drop the last sender to stop `rx` waiting for message.
+//! // The program will not complete if we comment this out.
+//! // **All** `tx` needs to be dropped for `rx` to have `Err`.
+//! drop(tx);
+//!
+//! // Unbounded receiver waiting for all senders to complete.
+//! while let Ok(msg) = rx.recv() {
+//! println!("{msg}");
+//! }
+//!
+//! println!("completed");
+//! ```
+
+#![stable(feature = "rust1", since = "1.0.0")]
+
+#[cfg(all(test, not(target_os = "emscripten")))]
+mod tests;
+
+#[cfg(all(test, not(target_os = "emscripten")))]
+mod sync_tests;
+
+// A description of how Rust's channel implementation works
+//
+// Channels are supposed to be the basic building block for all other
+// concurrent primitives that are used in Rust. As a result, the channel type
+// needs to be highly optimized, flexible, and broad enough for use everywhere.
+//
+// The choice of implementation of all channels is to be built on lock-free data
+// structures. The channels themselves are then consequently also lock-free data
+// structures. As always with lock-free code, this is a very "here be dragons"
+// territory, especially because I'm unaware of any academic papers that have
+// gone into great length about channels of these flavors.
+//
+// ## Flavors of channels
+//
+// From the perspective of a consumer of this library, there is only one flavor
+// of channel. This channel can be used as a stream and cloned to allow multiple
+// senders. Under the hood, however, there are actually three flavors of
+// channels in play.
+//
+// * Flavor::Oneshots - these channels are highly optimized for the one-send use
+// case. They contain as few atomics as possible and
+// involve one and exactly one allocation.
+// * Streams - these channels are optimized for the non-shared use case. They
+// use a different concurrent queue that is more tailored for this
+// use case. The initial allocation of this flavor of channel is not
+// optimized.
+// * Shared - this is the most general form of channel that this module offers,
+// a channel with multiple senders. This type is as optimized as it
+// can be, but the previous two types mentioned are much faster for
+// their use-cases.
+//
+// ## Concurrent queues
+//
+// The basic idea of Rust's Sender/Receiver types is that send() never blocks,
+// but recv() obviously blocks. This means that under the hood there must be
+// some shared and concurrent queue holding all of the actual data.
+//
+// With two flavors of channels, two flavors of queues are also used. We have
+// chosen to use queues from a well-known author that are abbreviated as SPSC
+// and MPSC (single producer, single consumer and multiple producer, single
+// consumer). SPSC queues are used for streams while MPSC queues are used for
+// shared channels.
+//
+// ### SPSC optimizations
+//
+// The SPSC queue found online is essentially a linked list of nodes where one
+// half of the nodes are the "queue of data" and the other half of nodes are a
+// cache of unused nodes. The unused nodes are used such that an allocation is
+// not required on every push() and a free doesn't need to happen on every
+// pop().
+//
+// As found online, however, the cache of nodes is of an infinite size. This
+// means that if a channel at one point in its life had 50k items in the queue,
+// then the queue will always have the capacity for 50k items. I believed that
+// this was an unnecessary limitation of the implementation, so I have altered
+// the queue to optionally have a bound on the cache size.
+//
+// By default, streams will have an unbounded SPSC queue with a small-ish cache
+// size. The hope is that the cache is still large enough to have very fast
+// send() operations while not too large such that millions of channels can
+// coexist at once.
+//
+// ### MPSC optimizations
+//
+// Right now the MPSC queue has not been optimized. Like the SPSC queue, it uses
+// a linked list under the hood to earn its unboundedness, but I have not put
+// forth much effort into having a cache of nodes similar to the SPSC queue.
+//
+// For now, I believe that this is "ok" because shared channels are not the most
+// common type, but soon we may wish to revisit this queue choice and determine
+// another candidate for backend storage of shared channels.
+//
+// ## Overview of the Implementation
+//
+// Now that there's a little background on the concurrent queues used, it's
+// worth going into much more detail about the channels themselves. The basic
+// pseudocode for a send/recv are:
+//
+//
+// send(t) recv()
+// queue.push(t) return if queue.pop()
+// if increment() == -1 deschedule {
+// wakeup() if decrement() > 0
+// cancel_deschedule()
+// }
+// queue.pop()
+//
+// As mentioned before, there are no locks in this implementation, only atomic
+// instructions are used.
+//
+// ### The internal atomic counter
+//
+// Every channel has a shared counter with each half to keep track of the size
+// of the queue. This counter is used to abort descheduling by the receiver and
+// to know when to wake up on the sending side.
+//
+// As seen in the pseudocode, senders will increment this count and receivers
+// will decrement the count. The theory behind this is that if a sender sees a
+// -1 count, it will wake up the receiver, and if the receiver sees a 1+ count,
+// then it doesn't need to block.
+//
+// The recv() method has a beginning call to pop(), and if successful, it needs
+// to decrement the count. It is a crucial implementation detail that this
+// decrement does *not* happen to the shared counter. If this were the case,
+// then it would be possible for the counter to be very negative when there were
+// no receivers waiting, in which case the senders would have to determine when
+// it was actually appropriate to wake up a receiver.
+//
+// Instead, the "steal count" is kept track of separately (not atomically
+// because it's only used by receivers), and then the decrement() call when
+// descheduling will lump in all of the recent steals into one large decrement.
+//
+// The implication of this is that if a sender sees a -1 count, then there's
+// guaranteed to be a waiter waiting!
+//
+// ## Native Implementation
+//
+// A major goal of these channels is to work seamlessly on and off the runtime.
+// All of the previous race conditions have been worded in terms of
+// scheduler-isms (which is obviously not available without the runtime).
+//
+// For now, native usage of channels (off the runtime) will fall back onto
+// mutexes/cond vars for descheduling/atomic decisions. The no-contention path
+// is still entirely lock-free, the "deschedule" blocks above are surrounded by
+// a mutex and the "wakeup" blocks involve grabbing a mutex and signaling on a
+// condition variable.
+//
+// ## Select
+//
+// Being able to support selection over channels has greatly influenced this
+// design, and not only does selection need to work inside the runtime, but also
+// outside the runtime.
+//
+// The implementation is fairly straightforward. The goal of select() is not to
+// return some data, but only to return which channel can receive data without
+// blocking. The implementation is essentially the entire blocking procedure
+// followed by an increment as soon as its woken up. The cancellation procedure
+// involves an increment and swapping out of to_wake to acquire ownership of the
+// thread to unblock.
+//
+// Sadly this current implementation requires multiple allocations, so I have
+// seen the throughput of select() be much worse than it should be. I do not
+// believe that there is anything fundamental that needs to change about these
+// channels, however, in order to support a more efficient select().
+//
+// FIXME: Select is now removed, so these factors are ready to be cleaned up!
+//
+// # Conclusion
+//
+// And now that you've seen all the races that I found and attempted to fix,
+// here's the code for you to find some more!
+
+use crate::cell::UnsafeCell;
+use crate::error;
+use crate::fmt;
+use crate::mem;
+use crate::sync::Arc;
+use crate::time::{Duration, Instant};
+
+mod blocking;
+mod mpsc_queue;
+mod oneshot;
+mod shared;
+mod spsc_queue;
+mod stream;
+mod sync;
+
+mod cache_aligned;
+
+/// The receiving half of Rust's [`channel`] (or [`sync_channel`]) type.
+/// This half can only be owned by one thread.
+///
+/// Messages sent to the channel can be retrieved using [`recv`].
+///
+/// [`recv`]: Receiver::recv
+///
+/// # Examples
+///
+/// ```rust
+/// use std::sync::mpsc::channel;
+/// use std::thread;
+/// use std::time::Duration;
+///
+/// let (send, recv) = channel();
+///
+/// thread::spawn(move || {
+/// send.send("Hello world!").unwrap();
+/// thread::sleep(Duration::from_secs(2)); // block for two seconds
+/// send.send("Delayed for 2 seconds").unwrap();
+/// });
+///
+/// println!("{}", recv.recv().unwrap()); // Received immediately
+/// println!("Waiting...");
+/// println!("{}", recv.recv().unwrap()); // Received after 2 seconds
+/// ```
+#[stable(feature = "rust1", since = "1.0.0")]
+#[cfg_attr(not(test), rustc_diagnostic_item = "Receiver")]
+pub struct Receiver<T> {
+ inner: UnsafeCell<Flavor<T>>,
+}
+
+// The receiver port can be sent from place to place, so long as it
+// is not used to receive non-sendable things.
+#[stable(feature = "rust1", since = "1.0.0")]
+unsafe impl<T: Send> Send for Receiver<T> {}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T> !Sync for Receiver<T> {}
+
+/// An iterator over messages on a [`Receiver`], created by [`iter`].
+///
+/// This iterator will block whenever [`next`] is called,
+/// waiting for a new message, and [`None`] will be returned
+/// when the corresponding channel has hung up.
+///
+/// [`iter`]: Receiver::iter
+/// [`next`]: Iterator::next
+///
+/// # Examples
+///
+/// ```rust
+/// use std::sync::mpsc::channel;
+/// use std::thread;
+///
+/// let (send, recv) = channel();
+///
+/// thread::spawn(move || {
+/// send.send(1u8).unwrap();
+/// send.send(2u8).unwrap();
+/// send.send(3u8).unwrap();
+/// });
+///
+/// for x in recv.iter() {
+/// println!("Got: {x}");
+/// }
+/// ```
+#[stable(feature = "rust1", since = "1.0.0")]
+#[derive(Debug)]
+pub struct Iter<'a, T: 'a> {
+ rx: &'a Receiver<T>,
+}
+
+/// An iterator that attempts to yield all pending values for a [`Receiver`],
+/// created by [`try_iter`].
+///
+/// [`None`] will be returned when there are no pending values remaining or
+/// if the corresponding channel has hung up.
+///
+/// This iterator will never block the caller in order to wait for data to
+/// become available. Instead, it will return [`None`].
+///
+/// [`try_iter`]: Receiver::try_iter
+///
+/// # Examples
+///
+/// ```rust
+/// use std::sync::mpsc::channel;
+/// use std::thread;
+/// use std::time::Duration;
+///
+/// let (sender, receiver) = channel();
+///
+/// // Nothing is in the buffer yet
+/// assert!(receiver.try_iter().next().is_none());
+/// println!("Nothing in the buffer...");
+///
+/// thread::spawn(move || {
+/// sender.send(1).unwrap();
+/// sender.send(2).unwrap();
+/// sender.send(3).unwrap();
+/// });
+///
+/// println!("Going to sleep...");
+/// thread::sleep(Duration::from_secs(2)); // block for two seconds
+///
+/// for x in receiver.try_iter() {
+/// println!("Got: {x}");
+/// }
+/// ```
+#[stable(feature = "receiver_try_iter", since = "1.15.0")]
+#[derive(Debug)]
+pub struct TryIter<'a, T: 'a> {
+ rx: &'a Receiver<T>,
+}
+
+/// An owning iterator over messages on a [`Receiver`],
+/// created by [`into_iter`].
+///
+/// This iterator will block whenever [`next`]
+/// is called, waiting for a new message, and [`None`] will be
+/// returned if the corresponding channel has hung up.
+///
+/// [`into_iter`]: Receiver::into_iter
+/// [`next`]: Iterator::next
+///
+/// # Examples
+///
+/// ```rust
+/// use std::sync::mpsc::channel;
+/// use std::thread;
+///
+/// let (send, recv) = channel();
+///
+/// thread::spawn(move || {
+/// send.send(1u8).unwrap();
+/// send.send(2u8).unwrap();
+/// send.send(3u8).unwrap();
+/// });
+///
+/// for x in recv.into_iter() {
+/// println!("Got: {x}");
+/// }
+/// ```
+#[stable(feature = "receiver_into_iter", since = "1.1.0")]
+#[derive(Debug)]
+pub struct IntoIter<T> {
+ rx: Receiver<T>,
+}
+
+/// The sending-half of Rust's asynchronous [`channel`] type. This half can only be
+/// owned by one thread, but it can be cloned to send to other threads.
+///
+/// Messages can be sent through this channel with [`send`].
+///
+/// Note: all senders (the original and the clones) need to be dropped for the receiver
+/// to stop blocking to receive messages with [`Receiver::recv`].
+///
+/// [`send`]: Sender::send
+///
+/// # Examples
+///
+/// ```rust
+/// use std::sync::mpsc::channel;
+/// use std::thread;
+///
+/// let (sender, receiver) = channel();
+/// let sender2 = sender.clone();
+///
+/// // First thread owns sender
+/// thread::spawn(move || {
+/// sender.send(1).unwrap();
+/// });
+///
+/// // Second thread owns sender2
+/// thread::spawn(move || {
+/// sender2.send(2).unwrap();
+/// });
+///
+/// let msg = receiver.recv().unwrap();
+/// let msg2 = receiver.recv().unwrap();
+///
+/// assert_eq!(3, msg + msg2);
+/// ```
+#[stable(feature = "rust1", since = "1.0.0")]
+pub struct Sender<T> {
+ inner: UnsafeCell<Flavor<T>>,
+}
+
+// The send port can be sent from place to place, so long as it
+// is not used to send non-sendable things.
+#[stable(feature = "rust1", since = "1.0.0")]
+unsafe impl<T: Send> Send for Sender<T> {}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T> !Sync for Sender<T> {}
+
+/// The sending-half of Rust's synchronous [`sync_channel`] type.
+///
+/// Messages can be sent through this channel with [`send`] or [`try_send`].
+///
+/// [`send`] will block if there is no space in the internal buffer.
+///
+/// [`send`]: SyncSender::send
+/// [`try_send`]: SyncSender::try_send
+///
+/// # Examples
+///
+/// ```rust
+/// use std::sync::mpsc::sync_channel;
+/// use std::thread;
+///
+/// // Create a sync_channel with buffer size 2
+/// let (sync_sender, receiver) = sync_channel(2);
+/// let sync_sender2 = sync_sender.clone();
+///
+/// // First thread owns sync_sender
+/// thread::spawn(move || {
+/// sync_sender.send(1).unwrap();
+/// sync_sender.send(2).unwrap();
+/// });
+///
+/// // Second thread owns sync_sender2
+/// thread::spawn(move || {
+/// sync_sender2.send(3).unwrap();
+/// // thread will now block since the buffer is full
+/// println!("Thread unblocked!");
+/// });
+///
+/// let mut msg;
+///
+/// msg = receiver.recv().unwrap();
+/// println!("message {msg} received");
+///
+/// // "Thread unblocked!" will be printed now
+///
+/// msg = receiver.recv().unwrap();
+/// println!("message {msg} received");
+///
+/// msg = receiver.recv().unwrap();
+///
+/// println!("message {msg} received");
+/// ```
+#[stable(feature = "rust1", since = "1.0.0")]
+pub struct SyncSender<T> {
+ inner: Arc<sync::Packet<T>>,
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+unsafe impl<T: Send> Send for SyncSender<T> {}
+
+/// An error returned from the [`Sender::send`] or [`SyncSender::send`]
+/// function on **channel**s.
+///
+/// A **send** operation can only fail if the receiving end of a channel is
+/// disconnected, implying that the data could never be received. The error
+/// contains the data being sent as a payload so it can be recovered.
+#[stable(feature = "rust1", since = "1.0.0")]
+#[derive(PartialEq, Eq, Clone, Copy)]
+pub struct SendError<T>(#[stable(feature = "rust1", since = "1.0.0")] pub T);
+
+/// An error returned from the [`recv`] function on a [`Receiver`].
+///
+/// The [`recv`] operation can only fail if the sending half of a
+/// [`channel`] (or [`sync_channel`]) is disconnected, implying that no further
+/// messages will ever be received.
+///
+/// [`recv`]: Receiver::recv
+#[derive(PartialEq, Eq, Clone, Copy, Debug)]
+#[stable(feature = "rust1", since = "1.0.0")]
+pub struct RecvError;
+
+/// This enumeration is the list of the possible reasons that [`try_recv`] could
+/// not return data when called. This can occur with both a [`channel`] and
+/// a [`sync_channel`].
+///
+/// [`try_recv`]: Receiver::try_recv
+#[derive(PartialEq, Eq, Clone, Copy, Debug)]
+#[stable(feature = "rust1", since = "1.0.0")]
+pub enum TryRecvError {
+ /// This **channel** is currently empty, but the **Sender**(s) have not yet
+ /// disconnected, so data may yet become available.
+ #[stable(feature = "rust1", since = "1.0.0")]
+ Empty,
+
+ /// The **channel**'s sending half has become disconnected, and there will
+ /// never be any more data received on it.
+ #[stable(feature = "rust1", since = "1.0.0")]
+ Disconnected,
+}
+
+/// This enumeration is the list of possible errors that made [`recv_timeout`]
+/// unable to return data when called. This can occur with both a [`channel`] and
+/// a [`sync_channel`].
+///
+/// [`recv_timeout`]: Receiver::recv_timeout
+#[derive(PartialEq, Eq, Clone, Copy, Debug)]
+#[stable(feature = "mpsc_recv_timeout", since = "1.12.0")]
+pub enum RecvTimeoutError {
+ /// This **channel** is currently empty, but the **Sender**(s) have not yet
+ /// disconnected, so data may yet become available.
+ #[stable(feature = "mpsc_recv_timeout", since = "1.12.0")]
+ Timeout,
+ /// The **channel**'s sending half has become disconnected, and there will
+ /// never be any more data received on it.
+ #[stable(feature = "mpsc_recv_timeout", since = "1.12.0")]
+ Disconnected,
+}
+
+/// This enumeration is the list of the possible error outcomes for the
+/// [`try_send`] method.
+///
+/// [`try_send`]: SyncSender::try_send
+#[stable(feature = "rust1", since = "1.0.0")]
+#[derive(PartialEq, Eq, Clone, Copy)]
+pub enum TrySendError<T> {
+ /// The data could not be sent on the [`sync_channel`] because it would require that
+ /// the callee block to send the data.
+ ///
+ /// If this is a buffered channel, then the buffer is full at this time. If
+ /// this is not a buffered channel, then there is no [`Receiver`] available to
+ /// acquire the data.
+ #[stable(feature = "rust1", since = "1.0.0")]
+ Full(#[stable(feature = "rust1", since = "1.0.0")] T),
+
+ /// This [`sync_channel`]'s receiving half has disconnected, so the data could not be
+ /// sent. The data is returned back to the callee in this case.
+ #[stable(feature = "rust1", since = "1.0.0")]
+ Disconnected(#[stable(feature = "rust1", since = "1.0.0")] T),
+}
+
+enum Flavor<T> {
+ Oneshot(Arc<oneshot::Packet<T>>),
+ Stream(Arc<stream::Packet<T>>),
+ Shared(Arc<shared::Packet<T>>),
+ Sync(Arc<sync::Packet<T>>),
+}
+
+#[doc(hidden)]
+trait UnsafeFlavor<T> {
+ fn inner_unsafe(&self) -> &UnsafeCell<Flavor<T>>;
+ unsafe fn inner_mut(&self) -> &mut Flavor<T> {
+ &mut *self.inner_unsafe().get()
+ }
+ unsafe fn inner(&self) -> &Flavor<T> {
+ &*self.inner_unsafe().get()
+ }
+}
+impl<T> UnsafeFlavor<T> for Sender<T> {
+ fn inner_unsafe(&self) -> &UnsafeCell<Flavor<T>> {
+ &self.inner
+ }
+}
+impl<T> UnsafeFlavor<T> for Receiver<T> {
+ fn inner_unsafe(&self) -> &UnsafeCell<Flavor<T>> {
+ &self.inner
+ }
+}
+
+/// Creates a new asynchronous channel, returning the sender/receiver halves.
+/// All data sent on the [`Sender`] will become available on the [`Receiver`] in
+/// the same order as it was sent, and no [`send`] will block the calling thread
+/// (this channel has an "infinite buffer", unlike [`sync_channel`], which will
+/// block after its buffer limit is reached). [`recv`] will block until a message
+/// is available while there is at least one [`Sender`] alive (including clones).
+///
+/// The [`Sender`] can be cloned to [`send`] to the same channel multiple times, but
+/// only one [`Receiver`] is supported.
+///
+/// If the [`Receiver`] is disconnected while trying to [`send`] with the
+/// [`Sender`], the [`send`] method will return a [`SendError`]. Similarly, if the
+/// [`Sender`] is disconnected while trying to [`recv`], the [`recv`] method will
+/// return a [`RecvError`].
+///
+/// [`send`]: Sender::send
+/// [`recv`]: Receiver::recv
+///
+/// # Examples
+///
+/// ```
+/// use std::sync::mpsc::channel;
+/// use std::thread;
+///
+/// let (sender, receiver) = channel();
+///
+/// // Spawn off an expensive computation
+/// thread::spawn(move|| {
+/// # fn expensive_computation() {}
+/// sender.send(expensive_computation()).unwrap();
+/// });
+///
+/// // Do some useful work for awhile
+///
+/// // Let's see what that answer was
+/// println!("{:?}", receiver.recv().unwrap());
+/// ```
+#[must_use]
+#[stable(feature = "rust1", since = "1.0.0")]
+pub fn channel<T>() -> (Sender<T>, Receiver<T>) {
+ let a = Arc::new(oneshot::Packet::new());
+ (Sender::new(Flavor::Oneshot(a.clone())), Receiver::new(Flavor::Oneshot(a)))
+}
+
+/// Creates a new synchronous, bounded channel.
+/// All data sent on the [`SyncSender`] will become available on the [`Receiver`]
+/// in the same order as it was sent. Like asynchronous [`channel`]s, the
+/// [`Receiver`] will block until a message becomes available. `sync_channel`
+/// differs greatly in the semantics of the sender, however.
+///
+/// This channel has an internal buffer on which messages will be queued.
+/// `bound` specifies the buffer size. When the internal buffer becomes full,
+/// future sends will *block* waiting for the buffer to open up. Note that a
+/// buffer size of 0 is valid, in which case this becomes "rendezvous channel"
+/// where each [`send`] will not return until a [`recv`] is paired with it.
+///
+/// The [`SyncSender`] can be cloned to [`send`] to the same channel multiple
+/// times, but only one [`Receiver`] is supported.
+///
+/// Like asynchronous channels, if the [`Receiver`] is disconnected while trying
+/// to [`send`] with the [`SyncSender`], the [`send`] method will return a
+/// [`SendError`]. Similarly, If the [`SyncSender`] is disconnected while trying
+/// to [`recv`], the [`recv`] method will return a [`RecvError`].
+///
+/// [`send`]: SyncSender::send
+/// [`recv`]: Receiver::recv
+///
+/// # Examples
+///
+/// ```
+/// use std::sync::mpsc::sync_channel;
+/// use std::thread;
+///
+/// let (sender, receiver) = sync_channel(1);
+///
+/// // this returns immediately
+/// sender.send(1).unwrap();
+///
+/// thread::spawn(move|| {
+/// // this will block until the previous message has been received
+/// sender.send(2).unwrap();
+/// });
+///
+/// assert_eq!(receiver.recv().unwrap(), 1);
+/// assert_eq!(receiver.recv().unwrap(), 2);
+/// ```
+#[must_use]
+#[stable(feature = "rust1", since = "1.0.0")]
+pub fn sync_channel<T>(bound: usize) -> (SyncSender<T>, Receiver<T>) {
+ let a = Arc::new(sync::Packet::new(bound));
+ (SyncSender::new(a.clone()), Receiver::new(Flavor::Sync(a)))
+}
+
+////////////////////////////////////////////////////////////////////////////////
+// Sender
+////////////////////////////////////////////////////////////////////////////////
+
+impl<T> Sender<T> {
+ fn new(inner: Flavor<T>) -> Sender<T> {
+ Sender { inner: UnsafeCell::new(inner) }
+ }
+
+ /// Attempts to send a value on this channel, returning it back if it could
+ /// not be sent.
+ ///
+ /// A successful send occurs when it is determined that the other end of
+ /// the channel has not hung up already. An unsuccessful send would be one
+ /// where the corresponding receiver has already been deallocated. Note
+ /// that a return value of [`Err`] means that the data will never be
+ /// received, but a return value of [`Ok`] does *not* mean that the data
+ /// will be received. It is possible for the corresponding receiver to
+ /// hang up immediately after this function returns [`Ok`].
+ ///
+ /// This method will never block the current thread.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use std::sync::mpsc::channel;
+ ///
+ /// let (tx, rx) = channel();
+ ///
+ /// // This send is always successful
+ /// tx.send(1).unwrap();
+ ///
+ /// // This send will fail because the receiver is gone
+ /// drop(rx);
+ /// assert_eq!(tx.send(1).unwrap_err().0, 1);
+ /// ```
+ #[stable(feature = "rust1", since = "1.0.0")]
+ pub fn send(&self, t: T) -> Result<(), SendError<T>> {
+ let (new_inner, ret) = match *unsafe { self.inner() } {
+ Flavor::Oneshot(ref p) => {
+ if !p.sent() {
+ return p.send(t).map_err(SendError);
+ } else {
+ let a = Arc::new(stream::Packet::new());
+ let rx = Receiver::new(Flavor::Stream(a.clone()));
+ match p.upgrade(rx) {
+ oneshot::UpSuccess => {
+ let ret = a.send(t);
+ (a, ret)
+ }
+ oneshot::UpDisconnected => (a, Err(t)),
+ oneshot::UpWoke(token) => {
+ // This send cannot panic because the thread is
+ // asleep (we're looking at it), so the receiver
+ // can't go away.
+ a.send(t).ok().unwrap();
+ token.signal();
+ (a, Ok(()))
+ }
+ }
+ }
+ }
+ Flavor::Stream(ref p) => return p.send(t).map_err(SendError),
+ Flavor::Shared(ref p) => return p.send(t).map_err(SendError),
+ Flavor::Sync(..) => unreachable!(),
+ };
+
+ unsafe {
+ let tmp = Sender::new(Flavor::Stream(new_inner));
+ mem::swap(self.inner_mut(), tmp.inner_mut());
+ }
+ ret.map_err(SendError)
+ }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T> Clone for Sender<T> {
+ /// Clone a sender to send to other threads.
+ ///
+ /// Note, be aware of the lifetime of the sender because all senders
+ /// (including the original) need to be dropped in order for
+ /// [`Receiver::recv`] to stop blocking.
+ fn clone(&self) -> Sender<T> {
+ let packet = match *unsafe { self.inner() } {
+ Flavor::Oneshot(ref p) => {
+ let a = Arc::new(shared::Packet::new());
+ {
+ let guard = a.postinit_lock();
+ let rx = Receiver::new(Flavor::Shared(a.clone()));
+ let sleeper = match p.upgrade(rx) {
+ oneshot::UpSuccess | oneshot::UpDisconnected => None,
+ oneshot::UpWoke(task) => Some(task),
+ };
+ a.inherit_blocker(sleeper, guard);
+ }
+ a
+ }
+ Flavor::Stream(ref p) => {
+ let a = Arc::new(shared::Packet::new());
+ {
+ let guard = a.postinit_lock();
+ let rx = Receiver::new(Flavor::Shared(a.clone()));
+ let sleeper = match p.upgrade(rx) {
+ stream::UpSuccess | stream::UpDisconnected => None,
+ stream::UpWoke(task) => Some(task),
+ };
+ a.inherit_blocker(sleeper, guard);
+ }
+ a
+ }
+ Flavor::Shared(ref p) => {
+ p.clone_chan();
+ return Sender::new(Flavor::Shared(p.clone()));
+ }
+ Flavor::Sync(..) => unreachable!(),
+ };
+
+ unsafe {
+ let tmp = Sender::new(Flavor::Shared(packet.clone()));
+ mem::swap(self.inner_mut(), tmp.inner_mut());
+ }
+ Sender::new(Flavor::Shared(packet))
+ }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T> Drop for Sender<T> {
+ fn drop(&mut self) {
+ match *unsafe { self.inner() } {
+ Flavor::Oneshot(ref p) => p.drop_chan(),
+ Flavor::Stream(ref p) => p.drop_chan(),
+ Flavor::Shared(ref p) => p.drop_chan(),
+ Flavor::Sync(..) => unreachable!(),
+ }
+ }
+}
+
+#[stable(feature = "mpsc_debug", since = "1.8.0")]
+impl<T> fmt::Debug for Sender<T> {
+ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+ f.debug_struct("Sender").finish_non_exhaustive()
+ }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+// SyncSender
+////////////////////////////////////////////////////////////////////////////////
+
+impl<T> SyncSender<T> {
+ fn new(inner: Arc<sync::Packet<T>>) -> SyncSender<T> {
+ SyncSender { inner }
+ }
+
+ /// Sends a value on this synchronous channel.
+ ///
+ /// This function will *block* until space in the internal buffer becomes
+ /// available or a receiver is available to hand off the message to.
+ ///
+ /// Note that a successful send does *not* guarantee that the receiver will
+ /// ever see the data if there is a buffer on this channel. Items may be
+ /// enqueued in the internal buffer for the receiver to receive at a later
+ /// time. If the buffer size is 0, however, the channel becomes a rendezvous
+ /// channel and it guarantees that the receiver has indeed received
+ /// the data if this function returns success.
+ ///
+ /// This function will never panic, but it may return [`Err`] if the
+ /// [`Receiver`] has disconnected and is no longer able to receive
+ /// information.
+ ///
+ /// # Examples
+ ///
+ /// ```rust
+ /// use std::sync::mpsc::sync_channel;
+ /// use std::thread;
+ ///
+ /// // Create a rendezvous sync_channel with buffer size 0
+ /// let (sync_sender, receiver) = sync_channel(0);
+ ///
+ /// thread::spawn(move || {
+ /// println!("sending message...");
+ /// sync_sender.send(1).unwrap();
+ /// // Thread is now blocked until the message is received
+ ///
+ /// println!("...message received!");
+ /// });
+ ///
+ /// let msg = receiver.recv().unwrap();
+ /// assert_eq!(1, msg);
+ /// ```
+ #[stable(feature = "rust1", since = "1.0.0")]
+ pub fn send(&self, t: T) -> Result<(), SendError<T>> {
+ self.inner.send(t).map_err(SendError)
+ }
+
+ /// Attempts to send a value on this channel without blocking.
+ ///
+ /// This method differs from [`send`] by returning immediately if the
+ /// channel's buffer is full or no receiver is waiting to acquire some
+ /// data. Compared with [`send`], this function has two failure cases
+ /// instead of one (one for disconnection, one for a full buffer).
+ ///
+ /// See [`send`] for notes about guarantees of whether the
+ /// receiver has received the data or not if this function is successful.
+ ///
+ /// [`send`]: Self::send
+ ///
+ /// # Examples
+ ///
+ /// ```rust
+ /// use std::sync::mpsc::sync_channel;
+ /// use std::thread;
+ ///
+ /// // Create a sync_channel with buffer size 1
+ /// let (sync_sender, receiver) = sync_channel(1);
+ /// let sync_sender2 = sync_sender.clone();
+ ///
+ /// // First thread owns sync_sender
+ /// thread::spawn(move || {
+ /// sync_sender.send(1).unwrap();
+ /// sync_sender.send(2).unwrap();
+ /// // Thread blocked
+ /// });
+ ///
+ /// // Second thread owns sync_sender2
+ /// thread::spawn(move || {
+ /// // This will return an error and send
+ /// // no message if the buffer is full
+ /// let _ = sync_sender2.try_send(3);
+ /// });
+ ///
+ /// let mut msg;
+ /// msg = receiver.recv().unwrap();
+ /// println!("message {msg} received");
+ ///
+ /// msg = receiver.recv().unwrap();
+ /// println!("message {msg} received");
+ ///
+ /// // Third message may have never been sent
+ /// match receiver.try_recv() {
+ /// Ok(msg) => println!("message {msg} received"),
+ /// Err(_) => println!("the third message was never sent"),
+ /// }
+ /// ```
+ #[stable(feature = "rust1", since = "1.0.0")]
+ pub fn try_send(&self, t: T) -> Result<(), TrySendError<T>> {
+ self.inner.try_send(t)
+ }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T> Clone for SyncSender<T> {
+ fn clone(&self) -> SyncSender<T> {
+ self.inner.clone_chan();
+ SyncSender::new(self.inner.clone())
+ }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T> Drop for SyncSender<T> {
+ fn drop(&mut self) {
+ self.inner.drop_chan();
+ }
+}
+
+#[stable(feature = "mpsc_debug", since = "1.8.0")]
+impl<T> fmt::Debug for SyncSender<T> {
+ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+ f.debug_struct("SyncSender").finish_non_exhaustive()
+ }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+// Receiver
+////////////////////////////////////////////////////////////////////////////////
+
+impl<T> Receiver<T> {
+ fn new(inner: Flavor<T>) -> Receiver<T> {
+ Receiver { inner: UnsafeCell::new(inner) }
+ }
+
+ /// Attempts to return a pending value on this receiver without blocking.
+ ///
+ /// This method will never block the caller in order to wait for data to
+ /// become available. Instead, this will always return immediately with a
+ /// possible option of pending data on the channel.
+ ///
+ /// This is useful for a flavor of "optimistic check" before deciding to
+ /// block on a receiver.
+ ///
+ /// Compared with [`recv`], this function has two failure cases instead of one
+ /// (one for disconnection, one for an empty buffer).
+ ///
+ /// [`recv`]: Self::recv
+ ///
+ /// # Examples
+ ///
+ /// ```rust
+ /// use std::sync::mpsc::{Receiver, channel};
+ ///
+ /// let (_, receiver): (_, Receiver<i32>) = channel();
+ ///
+ /// assert!(receiver.try_recv().is_err());
+ /// ```
+ #[stable(feature = "rust1", since = "1.0.0")]
+ pub fn try_recv(&self) -> Result<T, TryRecvError> {
+ loop {
+ let new_port = match *unsafe { self.inner() } {
+ Flavor::Oneshot(ref p) => match p.try_recv() {
+ Ok(t) => return Ok(t),
+ Err(oneshot::Empty) => return Err(TryRecvError::Empty),
+ Err(oneshot::Disconnected) => return Err(TryRecvError::Disconnected),
+ Err(oneshot::Upgraded(rx)) => rx,
+ },
+ Flavor::Stream(ref p) => match p.try_recv() {
+ Ok(t) => return Ok(t),
+ Err(stream::Empty) => return Err(TryRecvError::Empty),
+ Err(stream::Disconnected) => return Err(TryRecvError::Disconnected),
+ Err(stream::Upgraded(rx)) => rx,
+ },
+ Flavor::Shared(ref p) => match p.try_recv() {
+ Ok(t) => return Ok(t),
+ Err(shared::Empty) => return Err(TryRecvError::Empty),
+ Err(shared::Disconnected) => return Err(TryRecvError::Disconnected),
+ },
+ Flavor::Sync(ref p) => match p.try_recv() {
+ Ok(t) => return Ok(t),
+ Err(sync::Empty) => return Err(TryRecvError::Empty),
+ Err(sync::Disconnected) => return Err(TryRecvError::Disconnected),
+ },
+ };
+ unsafe {
+ mem::swap(self.inner_mut(), new_port.inner_mut());
+ }
+ }
+ }
+
+ /// Attempts to wait for a value on this receiver, returning an error if the
+ /// corresponding channel has hung up.
+ ///
+ /// This function will always block the current thread if there is no data
+ /// available and it's possible for more data to be sent (at least one sender
+ /// still exists). Once a message is sent to the corresponding [`Sender`]
+ /// (or [`SyncSender`]), this receiver will wake up and return that
+ /// message.
+ ///
+ /// If the corresponding [`Sender`] has disconnected, or it disconnects while
+ /// this call is blocking, this call will wake up and return [`Err`] to
+ /// indicate that no more messages can ever be received on this channel.
+ /// However, since channels are buffered, messages sent before the disconnect
+ /// will still be properly received.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use std::sync::mpsc;
+ /// use std::thread;
+ ///
+ /// let (send, recv) = mpsc::channel();
+ /// let handle = thread::spawn(move || {
+ /// send.send(1u8).unwrap();
+ /// });
+ ///
+ /// handle.join().unwrap();
+ ///
+ /// assert_eq!(Ok(1), recv.recv());
+ /// ```
+ ///
+ /// Buffering behavior:
+ ///
+ /// ```
+ /// use std::sync::mpsc;
+ /// use std::thread;
+ /// use std::sync::mpsc::RecvError;
+ ///
+ /// let (send, recv) = mpsc::channel();
+ /// let handle = thread::spawn(move || {
+ /// send.send(1u8).unwrap();
+ /// send.send(2).unwrap();
+ /// send.send(3).unwrap();
+ /// drop(send);
+ /// });
+ ///
+ /// // wait for the thread to join so we ensure the sender is dropped
+ /// handle.join().unwrap();
+ ///
+ /// assert_eq!(Ok(1), recv.recv());
+ /// assert_eq!(Ok(2), recv.recv());
+ /// assert_eq!(Ok(3), recv.recv());
+ /// assert_eq!(Err(RecvError), recv.recv());
+ /// ```
+ #[stable(feature = "rust1", since = "1.0.0")]
+ pub fn recv(&self) -> Result<T, RecvError> {
+ loop {
+ let new_port = match *unsafe { self.inner() } {
+ Flavor::Oneshot(ref p) => match p.recv(None) {
+ Ok(t) => return Ok(t),
+ Err(oneshot::Disconnected) => return Err(RecvError),
+ Err(oneshot::Upgraded(rx)) => rx,
+ Err(oneshot::Empty) => unreachable!(),
+ },
+ Flavor::Stream(ref p) => match p.recv(None) {
+ Ok(t) => return Ok(t),
+ Err(stream::Disconnected) => return Err(RecvError),
+ Err(stream::Upgraded(rx)) => rx,
+ Err(stream::Empty) => unreachable!(),
+ },
+ Flavor::Shared(ref p) => match p.recv(None) {
+ Ok(t) => return Ok(t),
+ Err(shared::Disconnected) => return Err(RecvError),
+ Err(shared::Empty) => unreachable!(),
+ },
+ Flavor::Sync(ref p) => return p.recv(None).map_err(|_| RecvError),
+ };
+ unsafe {
+ mem::swap(self.inner_mut(), new_port.inner_mut());
+ }
+ }
+ }
+
+ /// Attempts to wait for a value on this receiver, returning an error if the
+ /// corresponding channel has hung up, or if it waits more than `timeout`.
+ ///
+ /// This function will always block the current thread if there is no data
+ /// available and it's possible for more data to be sent (at least one sender
+ /// still exists). Once a message is sent to the corresponding [`Sender`]
+ /// (or [`SyncSender`]), this receiver will wake up and return that
+ /// message.
+ ///
+ /// If the corresponding [`Sender`] has disconnected, or it disconnects while
+ /// this call is blocking, this call will wake up and return [`Err`] to
+ /// indicate that no more messages can ever be received on this channel.
+ /// However, since channels are buffered, messages sent before the disconnect
+ /// will still be properly received.
+ ///
+ /// # Known Issues
+ ///
+ /// There is currently a known issue (see [`#39364`]) that causes `recv_timeout`
+ /// to panic unexpectedly with the following example:
+ ///
+ /// ```no_run
+ /// use std::sync::mpsc::channel;
+ /// use std::thread;
+ /// use std::time::Duration;
+ ///
+ /// let (tx, rx) = channel::<String>();
+ ///
+ /// thread::spawn(move || {
+ /// let d = Duration::from_millis(10);
+ /// loop {
+ /// println!("recv");
+ /// let _r = rx.recv_timeout(d);
+ /// }
+ /// });
+ ///
+ /// thread::sleep(Duration::from_millis(100));
+ /// let _c1 = tx.clone();
+ ///
+ /// thread::sleep(Duration::from_secs(1));
+ /// ```
+ ///
+ /// [`#39364`]: https://github.com/rust-lang/rust/issues/39364
+ ///
+ /// # Examples
+ ///
+ /// Successfully receiving value before encountering timeout:
+ ///
+ /// ```no_run
+ /// use std::thread;
+ /// use std::time::Duration;
+ /// use std::sync::mpsc;
+ ///
+ /// let (send, recv) = mpsc::channel();
+ ///
+ /// thread::spawn(move || {
+ /// send.send('a').unwrap();
+ /// });
+ ///
+ /// assert_eq!(
+ /// recv.recv_timeout(Duration::from_millis(400)),
+ /// Ok('a')
+ /// );
+ /// ```
+ ///
+ /// Receiving an error upon reaching timeout:
+ ///
+ /// ```no_run
+ /// use std::thread;
+ /// use std::time::Duration;
+ /// use std::sync::mpsc;
+ ///
+ /// let (send, recv) = mpsc::channel();
+ ///
+ /// thread::spawn(move || {
+ /// thread::sleep(Duration::from_millis(800));
+ /// send.send('a').unwrap();
+ /// });
+ ///
+ /// assert_eq!(
+ /// recv.recv_timeout(Duration::from_millis(400)),
+ /// Err(mpsc::RecvTimeoutError::Timeout)
+ /// );
+ /// ```
+ #[stable(feature = "mpsc_recv_timeout", since = "1.12.0")]
+ pub fn recv_timeout(&self, timeout: Duration) -> Result<T, RecvTimeoutError> {
+ // Do an optimistic try_recv to avoid the performance impact of
+ // Instant::now() in the full-channel case.
+ match self.try_recv() {
+ Ok(result) => Ok(result),
+ Err(TryRecvError::Disconnected) => Err(RecvTimeoutError::Disconnected),
+ Err(TryRecvError::Empty) => match Instant::now().checked_add(timeout) {
+ Some(deadline) => self.recv_deadline(deadline),
+ // So far in the future that it's practically the same as waiting indefinitely.
+ None => self.recv().map_err(RecvTimeoutError::from),
+ },
+ }
+ }
+
+ /// Attempts to wait for a value on this receiver, returning an error if the
+ /// corresponding channel has hung up, or if `deadline` is reached.
+ ///
+ /// This function will always block the current thread if there is no data
+ /// available and it's possible for more data to be sent. Once a message is
+ /// sent to the corresponding [`Sender`] (or [`SyncSender`]), then this
+ /// receiver will wake up and return that message.
+ ///
+ /// If the corresponding [`Sender`] has disconnected, or it disconnects while
+ /// this call is blocking, this call will wake up and return [`Err`] to
+ /// indicate that no more messages can ever be received on this channel.
+ /// However, since channels are buffered, messages sent before the disconnect
+ /// will still be properly received.
+ ///
+ /// # Examples
+ ///
+ /// Successfully receiving value before reaching deadline:
+ ///
+ /// ```no_run
+ /// #![feature(deadline_api)]
+ /// use std::thread;
+ /// use std::time::{Duration, Instant};
+ /// use std::sync::mpsc;
+ ///
+ /// let (send, recv) = mpsc::channel();
+ ///
+ /// thread::spawn(move || {
+ /// send.send('a').unwrap();
+ /// });
+ ///
+ /// assert_eq!(
+ /// recv.recv_deadline(Instant::now() + Duration::from_millis(400)),
+ /// Ok('a')
+ /// );
+ /// ```
+ ///
+ /// Receiving an error upon reaching deadline:
+ ///
+ /// ```no_run
+ /// #![feature(deadline_api)]
+ /// use std::thread;
+ /// use std::time::{Duration, Instant};
+ /// use std::sync::mpsc;
+ ///
+ /// let (send, recv) = mpsc::channel();
+ ///
+ /// thread::spawn(move || {
+ /// thread::sleep(Duration::from_millis(800));
+ /// send.send('a').unwrap();
+ /// });
+ ///
+ /// assert_eq!(
+ /// recv.recv_deadline(Instant::now() + Duration::from_millis(400)),
+ /// Err(mpsc::RecvTimeoutError::Timeout)
+ /// );
+ /// ```
+ #[unstable(feature = "deadline_api", issue = "46316")]
+ pub fn recv_deadline(&self, deadline: Instant) -> Result<T, RecvTimeoutError> {
+ use self::RecvTimeoutError::*;
+
+ loop {
+ let port_or_empty = match *unsafe { self.inner() } {
+ Flavor::Oneshot(ref p) => match p.recv(Some(deadline)) {
+ Ok(t) => return Ok(t),
+ Err(oneshot::Disconnected) => return Err(Disconnected),
+ Err(oneshot::Upgraded(rx)) => Some(rx),
+ Err(oneshot::Empty) => None,
+ },
+ Flavor::Stream(ref p) => match p.recv(Some(deadline)) {
+ Ok(t) => return Ok(t),
+ Err(stream::Disconnected) => return Err(Disconnected),
+ Err(stream::Upgraded(rx)) => Some(rx),
+ Err(stream::Empty) => None,
+ },
+ Flavor::Shared(ref p) => match p.recv(Some(deadline)) {
+ Ok(t) => return Ok(t),
+ Err(shared::Disconnected) => return Err(Disconnected),
+ Err(shared::Empty) => None,
+ },
+ Flavor::Sync(ref p) => match p.recv(Some(deadline)) {
+ Ok(t) => return Ok(t),
+ Err(sync::Disconnected) => return Err(Disconnected),
+ Err(sync::Empty) => None,
+ },
+ };
+
+ if let Some(new_port) = port_or_empty {
+ unsafe {
+ mem::swap(self.inner_mut(), new_port.inner_mut());
+ }
+ }
+
+ // If we're already passed the deadline, and we're here without
+ // data, return a timeout, else try again.
+ if Instant::now() >= deadline {
+ return Err(Timeout);
+ }
+ }
+ }
+
+ /// Returns an iterator that will block waiting for messages, but never
+ /// [`panic!`]. It will return [`None`] when the channel has hung up.
+ ///
+ /// # Examples
+ ///
+ /// ```rust
+ /// use std::sync::mpsc::channel;
+ /// use std::thread;
+ ///
+ /// let (send, recv) = channel();
+ ///
+ /// thread::spawn(move || {
+ /// send.send(1).unwrap();
+ /// send.send(2).unwrap();
+ /// send.send(3).unwrap();
+ /// });
+ ///
+ /// let mut iter = recv.iter();
+ /// assert_eq!(iter.next(), Some(1));
+ /// assert_eq!(iter.next(), Some(2));
+ /// assert_eq!(iter.next(), Some(3));
+ /// assert_eq!(iter.next(), None);
+ /// ```
+ #[stable(feature = "rust1", since = "1.0.0")]
+ pub fn iter(&self) -> Iter<'_, T> {
+ Iter { rx: self }
+ }
+
+ /// Returns an iterator that will attempt to yield all pending values.
+ /// It will return `None` if there are no more pending values or if the
+ /// channel has hung up. The iterator will never [`panic!`] or block the
+ /// user by waiting for values.
+ ///
+ /// # Examples
+ ///
+ /// ```no_run
+ /// use std::sync::mpsc::channel;
+ /// use std::thread;
+ /// use std::time::Duration;
+ ///
+ /// let (sender, receiver) = channel();
+ ///
+ /// // nothing is in the buffer yet
+ /// assert!(receiver.try_iter().next().is_none());
+ ///
+ /// thread::spawn(move || {
+ /// thread::sleep(Duration::from_secs(1));
+ /// sender.send(1).unwrap();
+ /// sender.send(2).unwrap();
+ /// sender.send(3).unwrap();
+ /// });
+ ///
+ /// // nothing is in the buffer yet
+ /// assert!(receiver.try_iter().next().is_none());
+ ///
+ /// // block for two seconds
+ /// thread::sleep(Duration::from_secs(2));
+ ///
+ /// let mut iter = receiver.try_iter();
+ /// assert_eq!(iter.next(), Some(1));
+ /// assert_eq!(iter.next(), Some(2));
+ /// assert_eq!(iter.next(), Some(3));
+ /// assert_eq!(iter.next(), None);
+ /// ```
+ #[stable(feature = "receiver_try_iter", since = "1.15.0")]
+ pub fn try_iter(&self) -> TryIter<'_, T> {
+ TryIter { rx: self }
+ }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<'a, T> Iterator for Iter<'a, T> {
+ type Item = T;
+
+ fn next(&mut self) -> Option<T> {
+ self.rx.recv().ok()
+ }
+}
+
+#[stable(feature = "receiver_try_iter", since = "1.15.0")]
+impl<'a, T> Iterator for TryIter<'a, T> {
+ type Item = T;
+
+ fn next(&mut self) -> Option<T> {
+ self.rx.try_recv().ok()
+ }
+}
+
+#[stable(feature = "receiver_into_iter", since = "1.1.0")]
+impl<'a, T> IntoIterator for &'a Receiver<T> {
+ type Item = T;
+ type IntoIter = Iter<'a, T>;
+
+ fn into_iter(self) -> Iter<'a, T> {
+ self.iter()
+ }
+}
+
+#[stable(feature = "receiver_into_iter", since = "1.1.0")]
+impl<T> Iterator for IntoIter<T> {
+ type Item = T;
+ fn next(&mut self) -> Option<T> {
+ self.rx.recv().ok()
+ }
+}
+
+#[stable(feature = "receiver_into_iter", since = "1.1.0")]
+impl<T> IntoIterator for Receiver<T> {
+ type Item = T;
+ type IntoIter = IntoIter<T>;
+
+ fn into_iter(self) -> IntoIter<T> {
+ IntoIter { rx: self }
+ }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T> Drop for Receiver<T> {
+ fn drop(&mut self) {
+ match *unsafe { self.inner() } {
+ Flavor::Oneshot(ref p) => p.drop_port(),
+ Flavor::Stream(ref p) => p.drop_port(),
+ Flavor::Shared(ref p) => p.drop_port(),
+ Flavor::Sync(ref p) => p.drop_port(),
+ }
+ }
+}
+
+#[stable(feature = "mpsc_debug", since = "1.8.0")]
+impl<T> fmt::Debug for Receiver<T> {
+ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+ f.debug_struct("Receiver").finish_non_exhaustive()
+ }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T> fmt::Debug for SendError<T> {
+ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+ f.debug_struct("SendError").finish_non_exhaustive()
+ }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T> fmt::Display for SendError<T> {
+ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+ "sending on a closed channel".fmt(f)
+ }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T: Send> error::Error for SendError<T> {
+ #[allow(deprecated)]
+ fn description(&self) -> &str {
+ "sending on a closed channel"
+ }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T> fmt::Debug for TrySendError<T> {
+ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+ match *self {
+ TrySendError::Full(..) => "Full(..)".fmt(f),
+ TrySendError::Disconnected(..) => "Disconnected(..)".fmt(f),
+ }
+ }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T> fmt::Display for TrySendError<T> {
+ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+ match *self {
+ TrySendError::Full(..) => "sending on a full channel".fmt(f),
+ TrySendError::Disconnected(..) => "sending on a closed channel".fmt(f),
+ }
+ }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T: Send> error::Error for TrySendError<T> {
+ #[allow(deprecated)]
+ fn description(&self) -> &str {
+ match *self {
+ TrySendError::Full(..) => "sending on a full channel",
+ TrySendError::Disconnected(..) => "sending on a closed channel",
+ }
+ }
+}
+
+#[stable(feature = "mpsc_error_conversions", since = "1.24.0")]
+impl<T> From<SendError<T>> for TrySendError<T> {
+ /// Converts a `SendError<T>` into a `TrySendError<T>`.
+ ///
+ /// This conversion always returns a `TrySendError::Disconnected` containing the data in the `SendError<T>`.
+ ///
+ /// No data is allocated on the heap.
+ fn from(err: SendError<T>) -> TrySendError<T> {
+ match err {
+ SendError(t) => TrySendError::Disconnected(t),
+ }
+ }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl fmt::Display for RecvError {
+ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+ "receiving on a closed channel".fmt(f)
+ }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl error::Error for RecvError {
+ #[allow(deprecated)]
+ fn description(&self) -> &str {
+ "receiving on a closed channel"
+ }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl fmt::Display for TryRecvError {
+ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+ match *self {
+ TryRecvError::Empty => "receiving on an empty channel".fmt(f),
+ TryRecvError::Disconnected => "receiving on a closed channel".fmt(f),
+ }
+ }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl error::Error for TryRecvError {
+ #[allow(deprecated)]
+ fn description(&self) -> &str {
+ match *self {
+ TryRecvError::Empty => "receiving on an empty channel",
+ TryRecvError::Disconnected => "receiving on a closed channel",
+ }
+ }
+}
+
+#[stable(feature = "mpsc_error_conversions", since = "1.24.0")]
+impl From<RecvError> for TryRecvError {
+ /// Converts a `RecvError` into a `TryRecvError`.
+ ///
+ /// This conversion always returns `TryRecvError::Disconnected`.
+ ///
+ /// No data is allocated on the heap.
+ fn from(err: RecvError) -> TryRecvError {
+ match err {
+ RecvError => TryRecvError::Disconnected,
+ }
+ }
+}
+
+#[stable(feature = "mpsc_recv_timeout_error", since = "1.15.0")]
+impl fmt::Display for RecvTimeoutError {
+ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+ match *self {
+ RecvTimeoutError::Timeout => "timed out waiting on channel".fmt(f),
+ RecvTimeoutError::Disconnected => "channel is empty and sending half is closed".fmt(f),
+ }
+ }
+}
+
+#[stable(feature = "mpsc_recv_timeout_error", since = "1.15.0")]
+impl error::Error for RecvTimeoutError {
+ #[allow(deprecated)]
+ fn description(&self) -> &str {
+ match *self {
+ RecvTimeoutError::Timeout => "timed out waiting on channel",
+ RecvTimeoutError::Disconnected => "channel is empty and sending half is closed",
+ }
+ }
+}
+
+#[stable(feature = "mpsc_error_conversions", since = "1.24.0")]
+impl From<RecvError> for RecvTimeoutError {
+ /// Converts a `RecvError` into a `RecvTimeoutError`.
+ ///
+ /// This conversion always returns `RecvTimeoutError::Disconnected`.
+ ///
+ /// No data is allocated on the heap.
+ fn from(err: RecvError) -> RecvTimeoutError {
+ match err {
+ RecvError => RecvTimeoutError::Disconnected,
+ }
+ }
+}
diff --git a/library/std/src/sync/mpsc/mpsc_queue.rs b/library/std/src/sync/mpsc/mpsc_queue.rs
new file mode 100644
index 000000000..cdd64a5de
--- /dev/null
+++ b/library/std/src/sync/mpsc/mpsc_queue.rs
@@ -0,0 +1,117 @@
+//! A mostly lock-free multi-producer, single consumer queue.
+//!
+//! This module contains an implementation of a concurrent MPSC queue. This
+//! queue can be used to share data between threads, and is also used as the
+//! building block of channels in rust.
+//!
+//! Note that the current implementation of this queue has a caveat of the `pop`
+//! method, and see the method for more information about it. Due to this
+//! caveat, this queue might not be appropriate for all use-cases.
+
+// https://www.1024cores.net/home/lock-free-algorithms
+// /queues/non-intrusive-mpsc-node-based-queue
+
+#[cfg(all(test, not(target_os = "emscripten")))]
+mod tests;
+
+pub use self::PopResult::*;
+
+use core::cell::UnsafeCell;
+use core::ptr;
+
+use crate::boxed::Box;
+use crate::sync::atomic::{AtomicPtr, Ordering};
+
+/// A result of the `pop` function.
+pub enum PopResult<T> {
+ /// Some data has been popped
+ Data(T),
+ /// The queue is empty
+ Empty,
+ /// The queue is in an inconsistent state. Popping data should succeed, but
+ /// some pushers have yet to make enough progress in order allow a pop to
+ /// succeed. It is recommended that a pop() occur "in the near future" in
+ /// order to see if the sender has made progress or not
+ Inconsistent,
+}
+
+struct Node<T> {
+ next: AtomicPtr<Node<T>>,
+ value: Option<T>,
+}
+
+/// The multi-producer single-consumer structure. This is not cloneable, but it
+/// may be safely shared so long as it is guaranteed that there is only one
+/// popper at a time (many pushers are allowed).
+pub struct Queue<T> {
+ head: AtomicPtr<Node<T>>,
+ tail: UnsafeCell<*mut Node<T>>,
+}
+
+unsafe impl<T: Send> Send for Queue<T> {}
+unsafe impl<T: Send> Sync for Queue<T> {}
+
+impl<T> Node<T> {
+ unsafe fn new(v: Option<T>) -> *mut Node<T> {
+ Box::into_raw(box Node { next: AtomicPtr::new(ptr::null_mut()), value: v })
+ }
+}
+
+impl<T> Queue<T> {
+ /// Creates a new queue that is safe to share among multiple producers and
+ /// one consumer.
+ pub fn new() -> Queue<T> {
+ let stub = unsafe { Node::new(None) };
+ Queue { head: AtomicPtr::new(stub), tail: UnsafeCell::new(stub) }
+ }
+
+ /// Pushes a new value onto this queue.
+ pub fn push(&self, t: T) {
+ unsafe {
+ let n = Node::new(Some(t));
+ let prev = self.head.swap(n, Ordering::AcqRel);
+ (*prev).next.store(n, Ordering::Release);
+ }
+ }
+
+ /// Pops some data from this queue.
+ ///
+ /// Note that the current implementation means that this function cannot
+ /// return `Option<T>`. It is possible for this queue to be in an
+ /// inconsistent state where many pushes have succeeded and completely
+ /// finished, but pops cannot return `Some(t)`. This inconsistent state
+ /// happens when a pusher is pre-empted at an inopportune moment.
+ ///
+ /// This inconsistent state means that this queue does indeed have data, but
+ /// it does not currently have access to it at this time.
+ pub fn pop(&self) -> PopResult<T> {
+ unsafe {
+ let tail = *self.tail.get();
+ let next = (*tail).next.load(Ordering::Acquire);
+
+ if !next.is_null() {
+ *self.tail.get() = next;
+ assert!((*tail).value.is_none());
+ assert!((*next).value.is_some());
+ let ret = (*next).value.take().unwrap();
+ let _: Box<Node<T>> = Box::from_raw(tail);
+ return Data(ret);
+ }
+
+ if self.head.load(Ordering::Acquire) == tail { Empty } else { Inconsistent }
+ }
+ }
+}
+
+impl<T> Drop for Queue<T> {
+ fn drop(&mut self) {
+ unsafe {
+ let mut cur = *self.tail.get();
+ while !cur.is_null() {
+ let next = (*cur).next.load(Ordering::Relaxed);
+ let _: Box<Node<T>> = Box::from_raw(cur);
+ cur = next;
+ }
+ }
+ }
+}
diff --git a/library/std/src/sync/mpsc/mpsc_queue/tests.rs b/library/std/src/sync/mpsc/mpsc_queue/tests.rs
new file mode 100644
index 000000000..9f4f31ed0
--- /dev/null
+++ b/library/std/src/sync/mpsc/mpsc_queue/tests.rs
@@ -0,0 +1,47 @@
+use super::{Data, Empty, Inconsistent, Queue};
+use crate::sync::mpsc::channel;
+use crate::sync::Arc;
+use crate::thread;
+
+#[test]
+fn test_full() {
+ let q: Queue<Box<_>> = Queue::new();
+ q.push(Box::new(1));
+ q.push(Box::new(2));
+}
+
+#[test]
+fn test() {
+ let nthreads = 8;
+ let nmsgs = 1000;
+ let q = Queue::new();
+ match q.pop() {
+ Empty => {}
+ Inconsistent | Data(..) => panic!(),
+ }
+ let (tx, rx) = channel();
+ let q = Arc::new(q);
+
+ for _ in 0..nthreads {
+ let tx = tx.clone();
+ let q = q.clone();
+ thread::spawn(move || {
+ for i in 0..nmsgs {
+ q.push(i);
+ }
+ tx.send(()).unwrap();
+ });
+ }
+
+ let mut i = 0;
+ while i < nthreads * nmsgs {
+ match q.pop() {
+ Empty | Inconsistent => {}
+ Data(_) => i += 1,
+ }
+ }
+ drop(tx);
+ for _ in 0..nthreads {
+ rx.recv().unwrap();
+ }
+}
diff --git a/library/std/src/sync/mpsc/oneshot.rs b/library/std/src/sync/mpsc/oneshot.rs
new file mode 100644
index 000000000..0e259b8ae
--- /dev/null
+++ b/library/std/src/sync/mpsc/oneshot.rs
@@ -0,0 +1,315 @@
+/// Oneshot channels/ports
+///
+/// This is the initial flavor of channels/ports used for comm module. This is
+/// an optimization for the one-use case of a channel. The major optimization of
+/// this type is to have one and exactly one allocation when the chan/port pair
+/// is created.
+///
+/// Another possible optimization would be to not use an Arc box because
+/// in theory we know when the shared packet can be deallocated (no real need
+/// for the atomic reference counting), but I was having trouble how to destroy
+/// the data early in a drop of a Port.
+///
+/// # Implementation
+///
+/// Oneshots are implemented around one atomic usize variable. This variable
+/// indicates both the state of the port/chan but also contains any threads
+/// blocked on the port. All atomic operations happen on this one word.
+///
+/// In order to upgrade a oneshot channel, an upgrade is considered a disconnect
+/// on behalf of the channel side of things (it can be mentally thought of as
+/// consuming the port). This upgrade is then also stored in the shared packet.
+/// The one caveat to consider is that when a port sees a disconnected channel
+/// it must check for data because there is no "data plus upgrade" state.
+pub use self::Failure::*;
+use self::MyUpgrade::*;
+pub use self::UpgradeResult::*;
+
+use crate::cell::UnsafeCell;
+use crate::ptr;
+use crate::sync::atomic::{AtomicPtr, Ordering};
+use crate::sync::mpsc::blocking::{self, SignalToken};
+use crate::sync::mpsc::Receiver;
+use crate::time::Instant;
+
+// Various states you can find a port in.
+const EMPTY: *mut u8 = ptr::invalid_mut::<u8>(0); // initial state: no data, no blocked receiver
+const DATA: *mut u8 = ptr::invalid_mut::<u8>(1); // data ready for receiver to take
+const DISCONNECTED: *mut u8 = ptr::invalid_mut::<u8>(2); // channel is disconnected OR upgraded
+// Any other value represents a pointer to a SignalToken value. The
+// protocol ensures that when the state moves *to* a pointer,
+// ownership of the token is given to the packet, and when the state
+// moves *from* a pointer, ownership of the token is transferred to
+// whoever changed the state.
+
+pub struct Packet<T> {
+ // Internal state of the chan/port pair (stores the blocked thread as well)
+ state: AtomicPtr<u8>,
+ // One-shot data slot location
+ data: UnsafeCell<Option<T>>,
+ // when used for the second time, a oneshot channel must be upgraded, and
+ // this contains the slot for the upgrade
+ upgrade: UnsafeCell<MyUpgrade<T>>,
+}
+
+pub enum Failure<T> {
+ Empty,
+ Disconnected,
+ Upgraded(Receiver<T>),
+}
+
+pub enum UpgradeResult {
+ UpSuccess,
+ UpDisconnected,
+ UpWoke(SignalToken),
+}
+
+enum MyUpgrade<T> {
+ NothingSent,
+ SendUsed,
+ GoUp(Receiver<T>),
+}
+
+impl<T> Packet<T> {
+ pub fn new() -> Packet<T> {
+ Packet {
+ data: UnsafeCell::new(None),
+ upgrade: UnsafeCell::new(NothingSent),
+ state: AtomicPtr::new(EMPTY),
+ }
+ }
+
+ pub fn send(&self, t: T) -> Result<(), T> {
+ unsafe {
+ // Sanity check
+ match *self.upgrade.get() {
+ NothingSent => {}
+ _ => panic!("sending on a oneshot that's already sent on "),
+ }
+ assert!((*self.data.get()).is_none());
+ ptr::write(self.data.get(), Some(t));
+ ptr::write(self.upgrade.get(), SendUsed);
+
+ match self.state.swap(DATA, Ordering::SeqCst) {
+ // Sent the data, no one was waiting
+ EMPTY => Ok(()),
+
+ // Couldn't send the data, the port hung up first. Return the data
+ // back up the stack.
+ DISCONNECTED => {
+ self.state.swap(DISCONNECTED, Ordering::SeqCst);
+ ptr::write(self.upgrade.get(), NothingSent);
+ Err((&mut *self.data.get()).take().unwrap())
+ }
+
+ // Not possible, these are one-use channels
+ DATA => unreachable!(),
+
+ // There is a thread waiting on the other end. We leave the 'DATA'
+ // state inside so it'll pick it up on the other end.
+ ptr => {
+ SignalToken::from_raw(ptr).signal();
+ Ok(())
+ }
+ }
+ }
+ }
+
+ // Just tests whether this channel has been sent on or not, this is only
+ // safe to use from the sender.
+ pub fn sent(&self) -> bool {
+ unsafe { !matches!(*self.upgrade.get(), NothingSent) }
+ }
+
+ pub fn recv(&self, deadline: Option<Instant>) -> Result<T, Failure<T>> {
+ // Attempt to not block the thread (it's a little expensive). If it looks
+ // like we're not empty, then immediately go through to `try_recv`.
+ if self.state.load(Ordering::SeqCst) == EMPTY {
+ let (wait_token, signal_token) = blocking::tokens();
+ let ptr = unsafe { signal_token.to_raw() };
+
+ // race with senders to enter the blocking state
+ if self.state.compare_exchange(EMPTY, ptr, Ordering::SeqCst, Ordering::SeqCst).is_ok() {
+ if let Some(deadline) = deadline {
+ let timed_out = !wait_token.wait_max_until(deadline);
+ // Try to reset the state
+ if timed_out {
+ self.abort_selection().map_err(Upgraded)?;
+ }
+ } else {
+ wait_token.wait();
+ debug_assert!(self.state.load(Ordering::SeqCst) != EMPTY);
+ }
+ } else {
+ // drop the signal token, since we never blocked
+ drop(unsafe { SignalToken::from_raw(ptr) });
+ }
+ }
+
+ self.try_recv()
+ }
+
+ pub fn try_recv(&self) -> Result<T, Failure<T>> {
+ unsafe {
+ match self.state.load(Ordering::SeqCst) {
+ EMPTY => Err(Empty),
+
+ // We saw some data on the channel, but the channel can be used
+ // again to send us an upgrade. As a result, we need to re-insert
+ // into the channel that there's no data available (otherwise we'll
+ // just see DATA next time). This is done as a cmpxchg because if
+ // the state changes under our feet we'd rather just see that state
+ // change.
+ DATA => {
+ let _ = self.state.compare_exchange(
+ DATA,
+ EMPTY,
+ Ordering::SeqCst,
+ Ordering::SeqCst,
+ );
+ match (&mut *self.data.get()).take() {
+ Some(data) => Ok(data),
+ None => unreachable!(),
+ }
+ }
+
+ // There's no guarantee that we receive before an upgrade happens,
+ // and an upgrade flags the channel as disconnected, so when we see
+ // this we first need to check if there's data available and *then*
+ // we go through and process the upgrade.
+ DISCONNECTED => match (&mut *self.data.get()).take() {
+ Some(data) => Ok(data),
+ None => match ptr::replace(self.upgrade.get(), SendUsed) {
+ SendUsed | NothingSent => Err(Disconnected),
+ GoUp(upgrade) => Err(Upgraded(upgrade)),
+ },
+ },
+
+ // We are the sole receiver; there cannot be a blocking
+ // receiver already.
+ _ => unreachable!(),
+ }
+ }
+ }
+
+ // Returns whether the upgrade was completed. If the upgrade wasn't
+ // completed, then the port couldn't get sent to the other half (it will
+ // never receive it).
+ pub fn upgrade(&self, up: Receiver<T>) -> UpgradeResult {
+ unsafe {
+ let prev = match *self.upgrade.get() {
+ NothingSent => NothingSent,
+ SendUsed => SendUsed,
+ _ => panic!("upgrading again"),
+ };
+ ptr::write(self.upgrade.get(), GoUp(up));
+
+ match self.state.swap(DISCONNECTED, Ordering::SeqCst) {
+ // If the channel is empty or has data on it, then we're good to go.
+ // Senders will check the data before the upgrade (in case we
+ // plastered over the DATA state).
+ DATA | EMPTY => UpSuccess,
+
+ // If the other end is already disconnected, then we failed the
+ // upgrade. Be sure to trash the port we were given.
+ DISCONNECTED => {
+ ptr::replace(self.upgrade.get(), prev);
+ UpDisconnected
+ }
+
+ // If someone's waiting, we gotta wake them up
+ ptr => UpWoke(SignalToken::from_raw(ptr)),
+ }
+ }
+ }
+
+ pub fn drop_chan(&self) {
+ match self.state.swap(DISCONNECTED, Ordering::SeqCst) {
+ DATA | DISCONNECTED | EMPTY => {}
+
+ // If someone's waiting, we gotta wake them up
+ ptr => unsafe {
+ SignalToken::from_raw(ptr).signal();
+ },
+ }
+ }
+
+ pub fn drop_port(&self) {
+ match self.state.swap(DISCONNECTED, Ordering::SeqCst) {
+ // An empty channel has nothing to do, and a remotely disconnected
+ // channel also has nothing to do b/c we're about to run the drop
+ // glue
+ DISCONNECTED | EMPTY => {}
+
+ // There's data on the channel, so make sure we destroy it promptly.
+ // This is why not using an arc is a little difficult (need the box
+ // to stay valid while we take the data).
+ DATA => unsafe {
+ (&mut *self.data.get()).take().unwrap();
+ },
+
+ // We're the only ones that can block on this port
+ _ => unreachable!(),
+ }
+ }
+
+ ////////////////////////////////////////////////////////////////////////////
+ // select implementation
+ ////////////////////////////////////////////////////////////////////////////
+
+ // Remove a previous selecting thread from this port. This ensures that the
+ // blocked thread will no longer be visible to any other threads.
+ //
+ // The return value indicates whether there's data on this port.
+ pub fn abort_selection(&self) -> Result<bool, Receiver<T>> {
+ let state = match self.state.load(Ordering::SeqCst) {
+ // Each of these states means that no further activity will happen
+ // with regard to abortion selection
+ s @ (EMPTY | DATA | DISCONNECTED) => s,
+
+ // If we've got a blocked thread, then use an atomic to gain ownership
+ // of it (may fail)
+ ptr => self
+ .state
+ .compare_exchange(ptr, EMPTY, Ordering::SeqCst, Ordering::SeqCst)
+ .unwrap_or_else(|x| x),
+ };
+
+ // Now that we've got ownership of our state, figure out what to do
+ // about it.
+ match state {
+ EMPTY => unreachable!(),
+ // our thread used for select was stolen
+ DATA => Ok(true),
+
+ // If the other end has hung up, then we have complete ownership
+ // of the port. First, check if there was data waiting for us. This
+ // is possible if the other end sent something and then hung up.
+ //
+ // We then need to check to see if there was an upgrade requested,
+ // and if so, the upgraded port needs to have its selection aborted.
+ DISCONNECTED => unsafe {
+ if (*self.data.get()).is_some() {
+ Ok(true)
+ } else {
+ match ptr::replace(self.upgrade.get(), SendUsed) {
+ GoUp(port) => Err(port),
+ _ => Ok(true),
+ }
+ }
+ },
+
+ // We woke ourselves up from select.
+ ptr => unsafe {
+ drop(SignalToken::from_raw(ptr));
+ Ok(false)
+ },
+ }
+ }
+}
+
+impl<T> Drop for Packet<T> {
+ fn drop(&mut self) {
+ assert_eq!(self.state.load(Ordering::SeqCst), DISCONNECTED);
+ }
+}
diff --git a/library/std/src/sync/mpsc/shared.rs b/library/std/src/sync/mpsc/shared.rs
new file mode 100644
index 000000000..51917bd96
--- /dev/null
+++ b/library/std/src/sync/mpsc/shared.rs
@@ -0,0 +1,501 @@
+/// Shared channels.
+///
+/// This is the flavor of channels which are not necessarily optimized for any
+/// particular use case, but are the most general in how they are used. Shared
+/// channels are cloneable allowing for multiple senders.
+///
+/// High level implementation details can be found in the comment of the parent
+/// module. You'll also note that the implementation of the shared and stream
+/// channels are quite similar, and this is no coincidence!
+pub use self::Failure::*;
+use self::StartResult::*;
+
+use core::cmp;
+use core::intrinsics::abort;
+
+use crate::cell::UnsafeCell;
+use crate::ptr;
+use crate::sync::atomic::{AtomicBool, AtomicIsize, AtomicPtr, AtomicUsize, Ordering};
+use crate::sync::mpsc::blocking::{self, SignalToken};
+use crate::sync::mpsc::mpsc_queue as mpsc;
+use crate::sync::{Mutex, MutexGuard};
+use crate::thread;
+use crate::time::Instant;
+
+const DISCONNECTED: isize = isize::MIN;
+const FUDGE: isize = 1024;
+const MAX_REFCOUNT: usize = (isize::MAX) as usize;
+#[cfg(test)]
+const MAX_STEALS: isize = 5;
+#[cfg(not(test))]
+const MAX_STEALS: isize = 1 << 20;
+const EMPTY: *mut u8 = ptr::null_mut(); // initial state: no data, no blocked receiver
+
+pub struct Packet<T> {
+ queue: mpsc::Queue<T>,
+ cnt: AtomicIsize, // How many items are on this channel
+ steals: UnsafeCell<isize>, // How many times has a port received without blocking?
+ to_wake: AtomicPtr<u8>, // SignalToken for wake up
+
+ // The number of channels which are currently using this packet.
+ channels: AtomicUsize,
+
+ // See the discussion in Port::drop and the channel send methods for what
+ // these are used for
+ port_dropped: AtomicBool,
+ sender_drain: AtomicIsize,
+
+ // this lock protects various portions of this implementation during
+ // select()
+ select_lock: Mutex<()>,
+}
+
+pub enum Failure {
+ Empty,
+ Disconnected,
+}
+
+#[derive(PartialEq, Eq)]
+enum StartResult {
+ Installed,
+ Abort,
+}
+
+impl<T> Packet<T> {
+ // Creation of a packet *must* be followed by a call to postinit_lock
+ // and later by inherit_blocker
+ pub fn new() -> Packet<T> {
+ Packet {
+ queue: mpsc::Queue::new(),
+ cnt: AtomicIsize::new(0),
+ steals: UnsafeCell::new(0),
+ to_wake: AtomicPtr::new(EMPTY),
+ channels: AtomicUsize::new(2),
+ port_dropped: AtomicBool::new(false),
+ sender_drain: AtomicIsize::new(0),
+ select_lock: Mutex::new(()),
+ }
+ }
+
+ // This function should be used after newly created Packet
+ // was wrapped with an Arc
+ // In other case mutex data will be duplicated while cloning
+ // and that could cause problems on platforms where it is
+ // represented by opaque data structure
+ pub fn postinit_lock(&self) -> MutexGuard<'_, ()> {
+ self.select_lock.lock().unwrap()
+ }
+
+ // This function is used at the creation of a shared packet to inherit a
+ // previously blocked thread. This is done to prevent spurious wakeups of
+ // threads in select().
+ //
+ // This can only be called at channel-creation time
+ pub fn inherit_blocker(&self, token: Option<SignalToken>, guard: MutexGuard<'_, ()>) {
+ if let Some(token) = token {
+ assert_eq!(self.cnt.load(Ordering::SeqCst), 0);
+ assert_eq!(self.to_wake.load(Ordering::SeqCst), EMPTY);
+ self.to_wake.store(unsafe { token.to_raw() }, Ordering::SeqCst);
+ self.cnt.store(-1, Ordering::SeqCst);
+
+ // This store is a little sketchy. What's happening here is that
+ // we're transferring a blocker from a oneshot or stream channel to
+ // this shared channel. In doing so, we never spuriously wake them
+ // up and rather only wake them up at the appropriate time. This
+ // implementation of shared channels assumes that any blocking
+ // recv() will undo the increment of steals performed in try_recv()
+ // once the recv is complete. This thread that we're inheriting,
+ // however, is not in the middle of recv. Hence, the first time we
+ // wake them up, they're going to wake up from their old port, move
+ // on to the upgraded port, and then call the block recv() function.
+ //
+ // When calling this function, they'll find there's data immediately
+ // available, counting it as a steal. This in fact wasn't a steal
+ // because we appropriately blocked them waiting for data.
+ //
+ // To offset this bad increment, we initially set the steal count to
+ // -1. You'll find some special code in abort_selection() as well to
+ // ensure that this -1 steal count doesn't escape too far.
+ unsafe {
+ *self.steals.get() = -1;
+ }
+ }
+
+ // When the shared packet is constructed, we grabbed this lock. The
+ // purpose of this lock is to ensure that abort_selection() doesn't
+ // interfere with this method. After we unlock this lock, we're
+ // signifying that we're done modifying self.cnt and self.to_wake and
+ // the port is ready for the world to continue using it.
+ drop(guard);
+ }
+
+ pub fn send(&self, t: T) -> Result<(), T> {
+ // See Port::drop for what's going on
+ if self.port_dropped.load(Ordering::SeqCst) {
+ return Err(t);
+ }
+
+ // Note that the multiple sender case is a little trickier
+ // semantically than the single sender case. The logic for
+ // incrementing is "add and if disconnected store disconnected".
+ // This could end up leading some senders to believe that there
+ // wasn't a disconnect if in fact there was a disconnect. This means
+ // that while one thread is attempting to re-store the disconnected
+ // states, other threads could walk through merrily incrementing
+ // this very-negative disconnected count. To prevent senders from
+ // spuriously attempting to send when the channels is actually
+ // disconnected, the count has a ranged check here.
+ //
+ // This is also done for another reason. Remember that the return
+ // value of this function is:
+ //
+ // `true` == the data *may* be received, this essentially has no
+ // meaning
+ // `false` == the data will *never* be received, this has a lot of
+ // meaning
+ //
+ // In the SPSC case, we have a check of 'queue.is_empty()' to see
+ // whether the data was actually received, but this same condition
+ // means nothing in a multi-producer context. As a result, this
+ // preflight check serves as the definitive "this will never be
+ // received". Once we get beyond this check, we have permanently
+ // entered the realm of "this may be received"
+ if self.cnt.load(Ordering::SeqCst) < DISCONNECTED + FUDGE {
+ return Err(t);
+ }
+
+ self.queue.push(t);
+ match self.cnt.fetch_add(1, Ordering::SeqCst) {
+ -1 => {
+ self.take_to_wake().signal();
+ }
+
+ // In this case, we have possibly failed to send our data, and
+ // we need to consider re-popping the data in order to fully
+ // destroy it. We must arbitrate among the multiple senders,
+ // however, because the queues that we're using are
+ // single-consumer queues. In order to do this, all exiting
+ // pushers will use an atomic count in order to count those
+ // flowing through. Pushers who see 0 are required to drain as
+ // much as possible, and then can only exit when they are the
+ // only pusher (otherwise they must try again).
+ n if n < DISCONNECTED + FUDGE => {
+ // see the comment in 'try' for a shared channel for why this
+ // window of "not disconnected" is ok.
+ self.cnt.store(DISCONNECTED, Ordering::SeqCst);
+
+ if self.sender_drain.fetch_add(1, Ordering::SeqCst) == 0 {
+ loop {
+ // drain the queue, for info on the thread yield see the
+ // discussion in try_recv
+ loop {
+ match self.queue.pop() {
+ mpsc::Data(..) => {}
+ mpsc::Empty => break,
+ mpsc::Inconsistent => thread::yield_now(),
+ }
+ }
+ // maybe we're done, if we're not the last ones
+ // here, then we need to go try again.
+ if self.sender_drain.fetch_sub(1, Ordering::SeqCst) == 1 {
+ break;
+ }
+ }
+
+ // At this point, there may still be data on the queue,
+ // but only if the count hasn't been incremented and
+ // some other sender hasn't finished pushing data just
+ // yet. That sender in question will drain its own data.
+ }
+ }
+
+ // Can't make any assumptions about this case like in the SPSC case.
+ _ => {}
+ }
+
+ Ok(())
+ }
+
+ pub fn recv(&self, deadline: Option<Instant>) -> Result<T, Failure> {
+ // This code is essentially the exact same as that found in the stream
+ // case (see stream.rs)
+ match self.try_recv() {
+ Err(Empty) => {}
+ data => return data,
+ }
+
+ let (wait_token, signal_token) = blocking::tokens();
+ if self.decrement(signal_token) == Installed {
+ if let Some(deadline) = deadline {
+ let timed_out = !wait_token.wait_max_until(deadline);
+ if timed_out {
+ self.abort_selection(false);
+ }
+ } else {
+ wait_token.wait();
+ }
+ }
+
+ match self.try_recv() {
+ data @ Ok(..) => unsafe {
+ *self.steals.get() -= 1;
+ data
+ },
+ data => data,
+ }
+ }
+
+ // Essentially the exact same thing as the stream decrement function.
+ // Returns true if blocking should proceed.
+ fn decrement(&self, token: SignalToken) -> StartResult {
+ unsafe {
+ assert_eq!(
+ self.to_wake.load(Ordering::SeqCst),
+ EMPTY,
+ "This is a known bug in the Rust standard library. See https://github.com/rust-lang/rust/issues/39364"
+ );
+ let ptr = token.to_raw();
+ self.to_wake.store(ptr, Ordering::SeqCst);
+
+ let steals = ptr::replace(self.steals.get(), 0);
+
+ match self.cnt.fetch_sub(1 + steals, Ordering::SeqCst) {
+ DISCONNECTED => {
+ self.cnt.store(DISCONNECTED, Ordering::SeqCst);
+ }
+ // If we factor in our steals and notice that the channel has no
+ // data, we successfully sleep
+ n => {
+ assert!(n >= 0);
+ if n - steals <= 0 {
+ return Installed;
+ }
+ }
+ }
+
+ self.to_wake.store(EMPTY, Ordering::SeqCst);
+ drop(SignalToken::from_raw(ptr));
+ Abort
+ }
+ }
+
+ pub fn try_recv(&self) -> Result<T, Failure> {
+ let ret = match self.queue.pop() {
+ mpsc::Data(t) => Some(t),
+ mpsc::Empty => None,
+
+ // This is a bit of an interesting case. The channel is reported as
+ // having data available, but our pop() has failed due to the queue
+ // being in an inconsistent state. This means that there is some
+ // pusher somewhere which has yet to complete, but we are guaranteed
+ // that a pop will eventually succeed. In this case, we spin in a
+ // yield loop because the remote sender should finish their enqueue
+ // operation "very quickly".
+ //
+ // Avoiding this yield loop would require a different queue
+ // abstraction which provides the guarantee that after M pushes have
+ // succeeded, at least M pops will succeed. The current queues
+ // guarantee that if there are N active pushes, you can pop N times
+ // once all N have finished.
+ mpsc::Inconsistent => {
+ let data;
+ loop {
+ thread::yield_now();
+ match self.queue.pop() {
+ mpsc::Data(t) => {
+ data = t;
+ break;
+ }
+ mpsc::Empty => panic!("inconsistent => empty"),
+ mpsc::Inconsistent => {}
+ }
+ }
+ Some(data)
+ }
+ };
+ match ret {
+ // See the discussion in the stream implementation for why we
+ // might decrement steals.
+ Some(data) => unsafe {
+ if *self.steals.get() > MAX_STEALS {
+ match self.cnt.swap(0, Ordering::SeqCst) {
+ DISCONNECTED => {
+ self.cnt.store(DISCONNECTED, Ordering::SeqCst);
+ }
+ n => {
+ let m = cmp::min(n, *self.steals.get());
+ *self.steals.get() -= m;
+ self.bump(n - m);
+ }
+ }
+ assert!(*self.steals.get() >= 0);
+ }
+ *self.steals.get() += 1;
+ Ok(data)
+ },
+
+ // See the discussion in the stream implementation for why we try
+ // again.
+ None => {
+ match self.cnt.load(Ordering::SeqCst) {
+ n if n != DISCONNECTED => Err(Empty),
+ _ => {
+ match self.queue.pop() {
+ mpsc::Data(t) => Ok(t),
+ mpsc::Empty => Err(Disconnected),
+ // with no senders, an inconsistency is impossible.
+ mpsc::Inconsistent => unreachable!(),
+ }
+ }
+ }
+ }
+ }
+ }
+
+ // Prepares this shared packet for a channel clone, essentially just bumping
+ // a refcount.
+ pub fn clone_chan(&self) {
+ let old_count = self.channels.fetch_add(1, Ordering::SeqCst);
+
+ // See comments on Arc::clone() on why we do this (for `mem::forget`).
+ if old_count > MAX_REFCOUNT {
+ abort();
+ }
+ }
+
+ // Decrement the reference count on a channel. This is called whenever a
+ // Chan is dropped and may end up waking up a receiver. It's the receiver's
+ // responsibility on the other end to figure out that we've disconnected.
+ pub fn drop_chan(&self) {
+ match self.channels.fetch_sub(1, Ordering::SeqCst) {
+ 1 => {}
+ n if n > 1 => return,
+ n => panic!("bad number of channels left {n}"),
+ }
+
+ match self.cnt.swap(DISCONNECTED, Ordering::SeqCst) {
+ -1 => {
+ self.take_to_wake().signal();
+ }
+ DISCONNECTED => {}
+ n => {
+ assert!(n >= 0);
+ }
+ }
+ }
+
+ // See the long discussion inside of stream.rs for why the queue is drained,
+ // and why it is done in this fashion.
+ pub fn drop_port(&self) {
+ self.port_dropped.store(true, Ordering::SeqCst);
+ let mut steals = unsafe { *self.steals.get() };
+ while {
+ match self.cnt.compare_exchange(
+ steals,
+ DISCONNECTED,
+ Ordering::SeqCst,
+ Ordering::SeqCst,
+ ) {
+ Ok(_) => false,
+ Err(old) => old != DISCONNECTED,
+ }
+ } {
+ // See the discussion in 'try_recv' for why we yield
+ // control of this thread.
+ loop {
+ match self.queue.pop() {
+ mpsc::Data(..) => {
+ steals += 1;
+ }
+ mpsc::Empty | mpsc::Inconsistent => break,
+ }
+ }
+ }
+ }
+
+ // Consumes ownership of the 'to_wake' field.
+ fn take_to_wake(&self) -> SignalToken {
+ let ptr = self.to_wake.load(Ordering::SeqCst);
+ self.to_wake.store(EMPTY, Ordering::SeqCst);
+ assert!(ptr != EMPTY);
+ unsafe { SignalToken::from_raw(ptr) }
+ }
+
+ ////////////////////////////////////////////////////////////////////////////
+ // select implementation
+ ////////////////////////////////////////////////////////////////////////////
+
+ // increment the count on the channel (used for selection)
+ fn bump(&self, amt: isize) -> isize {
+ match self.cnt.fetch_add(amt, Ordering::SeqCst) {
+ DISCONNECTED => {
+ self.cnt.store(DISCONNECTED, Ordering::SeqCst);
+ DISCONNECTED
+ }
+ n => n,
+ }
+ }
+
+ // Cancels a previous thread waiting on this port, returning whether there's
+ // data on the port.
+ //
+ // This is similar to the stream implementation (hence fewer comments), but
+ // uses a different value for the "steals" variable.
+ pub fn abort_selection(&self, _was_upgrade: bool) -> bool {
+ // Before we do anything else, we bounce on this lock. The reason for
+ // doing this is to ensure that any upgrade-in-progress is gone and
+ // done with. Without this bounce, we can race with inherit_blocker
+ // about looking at and dealing with to_wake. Once we have acquired the
+ // lock, we are guaranteed that inherit_blocker is done.
+ {
+ let _guard = self.select_lock.lock().unwrap();
+ }
+
+ // Like the stream implementation, we want to make sure that the count
+ // on the channel goes non-negative. We don't know how negative the
+ // stream currently is, so instead of using a steal value of 1, we load
+ // the channel count and figure out what we should do to make it
+ // positive.
+ let steals = {
+ let cnt = self.cnt.load(Ordering::SeqCst);
+ if cnt < 0 && cnt != DISCONNECTED { -cnt } else { 0 }
+ };
+ let prev = self.bump(steals + 1);
+
+ if prev == DISCONNECTED {
+ assert_eq!(self.to_wake.load(Ordering::SeqCst), EMPTY);
+ true
+ } else {
+ let cur = prev + steals + 1;
+ assert!(cur >= 0);
+ if prev < 0 {
+ drop(self.take_to_wake());
+ } else {
+ while self.to_wake.load(Ordering::SeqCst) != EMPTY {
+ thread::yield_now();
+ }
+ }
+ unsafe {
+ // if the number of steals is -1, it was the pre-emptive -1 steal
+ // count from when we inherited a blocker. This is fine because
+ // we're just going to overwrite it with a real value.
+ let old = self.steals.get();
+ assert!(*old == 0 || *old == -1);
+ *old = steals;
+ prev >= 0
+ }
+ }
+ }
+}
+
+impl<T> Drop for Packet<T> {
+ fn drop(&mut self) {
+ // Note that this load is not only an assert for correctness about
+ // disconnection, but also a proper fence before the read of
+ // `to_wake`, so this assert cannot be removed with also removing
+ // the `to_wake` assert.
+ assert_eq!(self.cnt.load(Ordering::SeqCst), DISCONNECTED);
+ assert_eq!(self.to_wake.load(Ordering::SeqCst), EMPTY);
+ assert_eq!(self.channels.load(Ordering::SeqCst), 0);
+ }
+}
diff --git a/library/std/src/sync/mpsc/spsc_queue.rs b/library/std/src/sync/mpsc/spsc_queue.rs
new file mode 100644
index 000000000..7e745eb31
--- /dev/null
+++ b/library/std/src/sync/mpsc/spsc_queue.rs
@@ -0,0 +1,236 @@
+//! A single-producer single-consumer concurrent queue
+//!
+//! This module contains the implementation of an SPSC queue which can be used
+//! concurrently between two threads. This data structure is safe to use and
+//! enforces the semantics that there is one pusher and one popper.
+
+// https://www.1024cores.net/home/lock-free-algorithms/queues/unbounded-spsc-queue
+
+#[cfg(all(test, not(target_os = "emscripten")))]
+mod tests;
+
+use core::cell::UnsafeCell;
+use core::ptr;
+
+use crate::boxed::Box;
+use crate::sync::atomic::{AtomicPtr, AtomicUsize, Ordering};
+
+use super::cache_aligned::CacheAligned;
+
+// Node within the linked list queue of messages to send
+struct Node<T> {
+ // FIXME: this could be an uninitialized T if we're careful enough, and
+ // that would reduce memory usage (and be a bit faster).
+ // is it worth it?
+ value: Option<T>, // nullable for re-use of nodes
+ cached: bool, // This node goes into the node cache
+ next: AtomicPtr<Node<T>>, // next node in the queue
+}
+
+/// The single-producer single-consumer queue. This structure is not cloneable,
+/// but it can be safely shared in an Arc if it is guaranteed that there
+/// is only one popper and one pusher touching the queue at any one point in
+/// time.
+pub struct Queue<T, ProducerAddition = (), ConsumerAddition = ()> {
+ // consumer fields
+ consumer: CacheAligned<Consumer<T, ConsumerAddition>>,
+
+ // producer fields
+ producer: CacheAligned<Producer<T, ProducerAddition>>,
+}
+
+struct Consumer<T, Addition> {
+ tail: UnsafeCell<*mut Node<T>>, // where to pop from
+ tail_prev: AtomicPtr<Node<T>>, // where to pop from
+ cache_bound: usize, // maximum cache size
+ cached_nodes: AtomicUsize, // number of nodes marked as cacheable
+ addition: Addition,
+}
+
+struct Producer<T, Addition> {
+ head: UnsafeCell<*mut Node<T>>, // where to push to
+ first: UnsafeCell<*mut Node<T>>, // where to get new nodes from
+ tail_copy: UnsafeCell<*mut Node<T>>, // between first/tail
+ addition: Addition,
+}
+
+unsafe impl<T: Send, P: Send + Sync, C: Send + Sync> Send for Queue<T, P, C> {}
+
+unsafe impl<T: Send, P: Send + Sync, C: Send + Sync> Sync for Queue<T, P, C> {}
+
+impl<T> Node<T> {
+ fn new() -> *mut Node<T> {
+ Box::into_raw(box Node {
+ value: None,
+ cached: false,
+ next: AtomicPtr::new(ptr::null_mut::<Node<T>>()),
+ })
+ }
+}
+
+impl<T, ProducerAddition, ConsumerAddition> Queue<T, ProducerAddition, ConsumerAddition> {
+ /// Creates a new queue. With given additional elements in the producer and
+ /// consumer portions of the queue.
+ ///
+ /// Due to the performance implications of cache-contention,
+ /// we wish to keep fields used mainly by the producer on a separate cache
+ /// line than those used by the consumer.
+ /// Since cache lines are usually 64 bytes, it is unreasonably expensive to
+ /// allocate one for small fields, so we allow users to insert additional
+ /// fields into the cache lines already allocated by this for the producer
+ /// and consumer.
+ ///
+ /// This is unsafe as the type system doesn't enforce a single
+ /// consumer-producer relationship. It also allows the consumer to `pop`
+ /// items while there is a `peek` active due to all methods having a
+ /// non-mutable receiver.
+ ///
+ /// # Arguments
+ ///
+ /// * `bound` - This queue implementation is implemented with a linked
+ /// list, and this means that a push is always a malloc. In
+ /// order to amortize this cost, an internal cache of nodes is
+ /// maintained to prevent a malloc from always being
+ /// necessary. This bound is the limit on the size of the
+ /// cache (if desired). If the value is 0, then the cache has
+ /// no bound. Otherwise, the cache will never grow larger than
+ /// `bound` (although the queue itself could be much larger.
+ pub unsafe fn with_additions(
+ bound: usize,
+ producer_addition: ProducerAddition,
+ consumer_addition: ConsumerAddition,
+ ) -> Self {
+ let n1 = Node::new();
+ let n2 = Node::new();
+ (*n1).next.store(n2, Ordering::Relaxed);
+ Queue {
+ consumer: CacheAligned::new(Consumer {
+ tail: UnsafeCell::new(n2),
+ tail_prev: AtomicPtr::new(n1),
+ cache_bound: bound,
+ cached_nodes: AtomicUsize::new(0),
+ addition: consumer_addition,
+ }),
+ producer: CacheAligned::new(Producer {
+ head: UnsafeCell::new(n2),
+ first: UnsafeCell::new(n1),
+ tail_copy: UnsafeCell::new(n1),
+ addition: producer_addition,
+ }),
+ }
+ }
+
+ /// Pushes a new value onto this queue. Note that to use this function
+ /// safely, it must be externally guaranteed that there is only one pusher.
+ pub fn push(&self, t: T) {
+ unsafe {
+ // Acquire a node (which either uses a cached one or allocates a new
+ // one), and then append this to the 'head' node.
+ let n = self.alloc();
+ assert!((*n).value.is_none());
+ (*n).value = Some(t);
+ (*n).next.store(ptr::null_mut(), Ordering::Relaxed);
+ (**self.producer.head.get()).next.store(n, Ordering::Release);
+ *(&self.producer.head).get() = n;
+ }
+ }
+
+ unsafe fn alloc(&self) -> *mut Node<T> {
+ // First try to see if we can consume the 'first' node for our uses.
+ if *self.producer.first.get() != *self.producer.tail_copy.get() {
+ let ret = *self.producer.first.get();
+ *self.producer.0.first.get() = (*ret).next.load(Ordering::Relaxed);
+ return ret;
+ }
+ // If the above fails, then update our copy of the tail and try
+ // again.
+ *self.producer.0.tail_copy.get() = self.consumer.tail_prev.load(Ordering::Acquire);
+ if *self.producer.first.get() != *self.producer.tail_copy.get() {
+ let ret = *self.producer.first.get();
+ *self.producer.0.first.get() = (*ret).next.load(Ordering::Relaxed);
+ return ret;
+ }
+ // If all of that fails, then we have to allocate a new node
+ // (there's nothing in the node cache).
+ Node::new()
+ }
+
+ /// Attempts to pop a value from this queue. Remember that to use this type
+ /// safely you must ensure that there is only one popper at a time.
+ pub fn pop(&self) -> Option<T> {
+ unsafe {
+ // The `tail` node is not actually a used node, but rather a
+ // sentinel from where we should start popping from. Hence, look at
+ // tail's next field and see if we can use it. If we do a pop, then
+ // the current tail node is a candidate for going into the cache.
+ let tail = *self.consumer.tail.get();
+ let next = (*tail).next.load(Ordering::Acquire);
+ if next.is_null() {
+ return None;
+ }
+ assert!((*next).value.is_some());
+ let ret = (*next).value.take();
+
+ *self.consumer.0.tail.get() = next;
+ if self.consumer.cache_bound == 0 {
+ self.consumer.tail_prev.store(tail, Ordering::Release);
+ } else {
+ let cached_nodes = self.consumer.cached_nodes.load(Ordering::Relaxed);
+ if cached_nodes < self.consumer.cache_bound && !(*tail).cached {
+ self.consumer.cached_nodes.store(cached_nodes, Ordering::Relaxed);
+ (*tail).cached = true;
+ }
+
+ if (*tail).cached {
+ self.consumer.tail_prev.store(tail, Ordering::Release);
+ } else {
+ (*self.consumer.tail_prev.load(Ordering::Relaxed))
+ .next
+ .store(next, Ordering::Relaxed);
+ // We have successfully erased all references to 'tail', so
+ // now we can safely drop it.
+ let _: Box<Node<T>> = Box::from_raw(tail);
+ }
+ }
+ ret
+ }
+ }
+
+ /// Attempts to peek at the head of the queue, returning `None` if the queue
+ /// has no data currently
+ ///
+ /// # Warning
+ /// The reference returned is invalid if it is not used before the consumer
+ /// pops the value off the queue. If the producer then pushes another value
+ /// onto the queue, it will overwrite the value pointed to by the reference.
+ pub fn peek(&self) -> Option<&mut T> {
+ // This is essentially the same as above with all the popping bits
+ // stripped out.
+ unsafe {
+ let tail = *self.consumer.tail.get();
+ let next = (*tail).next.load(Ordering::Acquire);
+ if next.is_null() { None } else { (*next).value.as_mut() }
+ }
+ }
+
+ pub fn producer_addition(&self) -> &ProducerAddition {
+ &self.producer.addition
+ }
+
+ pub fn consumer_addition(&self) -> &ConsumerAddition {
+ &self.consumer.addition
+ }
+}
+
+impl<T, ProducerAddition, ConsumerAddition> Drop for Queue<T, ProducerAddition, ConsumerAddition> {
+ fn drop(&mut self) {
+ unsafe {
+ let mut cur = *self.producer.first.get();
+ while !cur.is_null() {
+ let next = (*cur).next.load(Ordering::Relaxed);
+ let _n: Box<Node<T>> = Box::from_raw(cur);
+ cur = next;
+ }
+ }
+ }
+}
diff --git a/library/std/src/sync/mpsc/spsc_queue/tests.rs b/library/std/src/sync/mpsc/spsc_queue/tests.rs
new file mode 100644
index 000000000..467ef3dbd
--- /dev/null
+++ b/library/std/src/sync/mpsc/spsc_queue/tests.rs
@@ -0,0 +1,101 @@
+use super::Queue;
+use crate::sync::mpsc::channel;
+use crate::sync::Arc;
+use crate::thread;
+
+#[test]
+fn smoke() {
+ unsafe {
+ let queue = Queue::with_additions(0, (), ());
+ queue.push(1);
+ queue.push(2);
+ assert_eq!(queue.pop(), Some(1));
+ assert_eq!(queue.pop(), Some(2));
+ assert_eq!(queue.pop(), None);
+ queue.push(3);
+ queue.push(4);
+ assert_eq!(queue.pop(), Some(3));
+ assert_eq!(queue.pop(), Some(4));
+ assert_eq!(queue.pop(), None);
+ }
+}
+
+#[test]
+fn peek() {
+ unsafe {
+ let queue = Queue::with_additions(0, (), ());
+ queue.push(vec![1]);
+
+ // Ensure the borrowchecker works
+ match queue.peek() {
+ Some(vec) => {
+ assert_eq!(&*vec, &[1]);
+ }
+ None => unreachable!(),
+ }
+
+ match queue.pop() {
+ Some(vec) => {
+ assert_eq!(&*vec, &[1]);
+ }
+ None => unreachable!(),
+ }
+ }
+}
+
+#[test]
+fn drop_full() {
+ unsafe {
+ let q: Queue<Box<_>> = Queue::with_additions(0, (), ());
+ q.push(Box::new(1));
+ q.push(Box::new(2));
+ }
+}
+
+#[test]
+fn smoke_bound() {
+ unsafe {
+ let q = Queue::with_additions(0, (), ());
+ q.push(1);
+ q.push(2);
+ assert_eq!(q.pop(), Some(1));
+ assert_eq!(q.pop(), Some(2));
+ assert_eq!(q.pop(), None);
+ q.push(3);
+ q.push(4);
+ assert_eq!(q.pop(), Some(3));
+ assert_eq!(q.pop(), Some(4));
+ assert_eq!(q.pop(), None);
+ }
+}
+
+#[test]
+fn stress() {
+ unsafe {
+ stress_bound(0);
+ stress_bound(1);
+ }
+
+ unsafe fn stress_bound(bound: usize) {
+ let q = Arc::new(Queue::with_additions(bound, (), ()));
+
+ let (tx, rx) = channel();
+ let q2 = q.clone();
+ let _t = thread::spawn(move || {
+ for _ in 0..100000 {
+ loop {
+ match q2.pop() {
+ Some(1) => break,
+ Some(_) => panic!(),
+ None => {}
+ }
+ }
+ }
+ tx.send(()).unwrap();
+ });
+ for _ in 0..100000 {
+ q.push(1);
+ }
+ rx.recv().unwrap();
+ }
+}
diff --git a/library/std/src/sync/mpsc/stream.rs b/library/std/src/sync/mpsc/stream.rs
new file mode 100644
index 000000000..4c3812c79
--- /dev/null
+++ b/library/std/src/sync/mpsc/stream.rs
@@ -0,0 +1,457 @@
+/// Stream channels
+///
+/// This is the flavor of channels which are optimized for one sender and one
+/// receiver. The sender will be upgraded to a shared channel if the channel is
+/// cloned.
+///
+/// High level implementation details can be found in the comment of the parent
+/// module.
+pub use self::Failure::*;
+use self::Message::*;
+pub use self::UpgradeResult::*;
+
+use core::cmp;
+
+use crate::cell::UnsafeCell;
+use crate::ptr;
+use crate::thread;
+use crate::time::Instant;
+
+use crate::sync::atomic::{AtomicBool, AtomicIsize, AtomicPtr, Ordering};
+use crate::sync::mpsc::blocking::{self, SignalToken};
+use crate::sync::mpsc::spsc_queue as spsc;
+use crate::sync::mpsc::Receiver;
+
+const DISCONNECTED: isize = isize::MIN;
+#[cfg(test)]
+const MAX_STEALS: isize = 5;
+#[cfg(not(test))]
+const MAX_STEALS: isize = 1 << 20;
+const EMPTY: *mut u8 = ptr::null_mut(); // initial state: no data, no blocked receiver
+
+pub struct Packet<T> {
+ // internal queue for all messages
+ queue: spsc::Queue<Message<T>, ProducerAddition, ConsumerAddition>,
+}
+
+struct ProducerAddition {
+ cnt: AtomicIsize, // How many items are on this channel
+ to_wake: AtomicPtr<u8>, // SignalToken for the blocked thread to wake up
+
+ port_dropped: AtomicBool, // flag if the channel has been destroyed.
+}
+
+struct ConsumerAddition {
+ steals: UnsafeCell<isize>, // How many times has a port received without blocking?
+}
+
+pub enum Failure<T> {
+ Empty,
+ Disconnected,
+ Upgraded(Receiver<T>),
+}
+
+pub enum UpgradeResult {
+ UpSuccess,
+ UpDisconnected,
+ UpWoke(SignalToken),
+}
+
+// Any message could contain an "upgrade request" to a new shared port, so the
+// internal queue it's a queue of T, but rather Message<T>
+enum Message<T> {
+ Data(T),
+ GoUp(Receiver<T>),
+}
+
+impl<T> Packet<T> {
+ pub fn new() -> Packet<T> {
+ Packet {
+ queue: unsafe {
+ spsc::Queue::with_additions(
+ 128,
+ ProducerAddition {
+ cnt: AtomicIsize::new(0),
+ to_wake: AtomicPtr::new(EMPTY),
+
+ port_dropped: AtomicBool::new(false),
+ },
+ ConsumerAddition { steals: UnsafeCell::new(0) },
+ )
+ },
+ }
+ }
+
+ pub fn send(&self, t: T) -> Result<(), T> {
+ // If the other port has deterministically gone away, then definitely
+ // must return the data back up the stack. Otherwise, the data is
+ // considered as being sent.
+ if self.queue.producer_addition().port_dropped.load(Ordering::SeqCst) {
+ return Err(t);
+ }
+
+ match self.do_send(Data(t)) {
+ UpSuccess | UpDisconnected => {}
+ UpWoke(token) => {
+ token.signal();
+ }
+ }
+ Ok(())
+ }
+
+ pub fn upgrade(&self, up: Receiver<T>) -> UpgradeResult {
+ // If the port has gone away, then there's no need to proceed any
+ // further.
+ if self.queue.producer_addition().port_dropped.load(Ordering::SeqCst) {
+ return UpDisconnected;
+ }
+
+ self.do_send(GoUp(up))
+ }
+
+ fn do_send(&self, t: Message<T>) -> UpgradeResult {
+ self.queue.push(t);
+ match self.queue.producer_addition().cnt.fetch_add(1, Ordering::SeqCst) {
+ // As described in the mod's doc comment, -1 == wakeup
+ -1 => UpWoke(self.take_to_wake()),
+ // As as described before, SPSC queues must be >= -2
+ -2 => UpSuccess,
+
+ // Be sure to preserve the disconnected state, and the return value
+ // in this case is going to be whether our data was received or not.
+ // This manifests itself on whether we have an empty queue or not.
+ //
+ // Primarily, are required to drain the queue here because the port
+ // will never remove this data. We can only have at most one item to
+ // drain (the port drains the rest).
+ DISCONNECTED => {
+ self.queue.producer_addition().cnt.store(DISCONNECTED, Ordering::SeqCst);
+ let first = self.queue.pop();
+ let second = self.queue.pop();
+ assert!(second.is_none());
+
+ match first {
+ Some(..) => UpSuccess, // we failed to send the data
+ None => UpDisconnected, // we successfully sent data
+ }
+ }
+
+ // Otherwise we just sent some data on a non-waiting queue, so just
+ // make sure the world is sane and carry on!
+ n => {
+ assert!(n >= 0);
+ UpSuccess
+ }
+ }
+ }
+
+ // Consumes ownership of the 'to_wake' field.
+ fn take_to_wake(&self) -> SignalToken {
+ let ptr = self.queue.producer_addition().to_wake.load(Ordering::SeqCst);
+ self.queue.producer_addition().to_wake.store(EMPTY, Ordering::SeqCst);
+ assert!(ptr != EMPTY);
+ unsafe { SignalToken::from_raw(ptr) }
+ }
+
+ // Decrements the count on the channel for a sleeper, returning the sleeper
+ // back if it shouldn't sleep. Note that this is the location where we take
+ // steals into account.
+ fn decrement(&self, token: SignalToken) -> Result<(), SignalToken> {
+ assert_eq!(self.queue.producer_addition().to_wake.load(Ordering::SeqCst), EMPTY);
+ let ptr = unsafe { token.to_raw() };
+ self.queue.producer_addition().to_wake.store(ptr, Ordering::SeqCst);
+
+ let steals = unsafe { ptr::replace(self.queue.consumer_addition().steals.get(), 0) };
+
+ match self.queue.producer_addition().cnt.fetch_sub(1 + steals, Ordering::SeqCst) {
+ DISCONNECTED => {
+ self.queue.producer_addition().cnt.store(DISCONNECTED, Ordering::SeqCst);
+ }
+ // If we factor in our steals and notice that the channel has no
+ // data, we successfully sleep
+ n => {
+ assert!(n >= 0);
+ if n - steals <= 0 {
+ return Ok(());
+ }
+ }
+ }
+
+ self.queue.producer_addition().to_wake.store(EMPTY, Ordering::SeqCst);
+ Err(unsafe { SignalToken::from_raw(ptr) })
+ }
+
+ pub fn recv(&self, deadline: Option<Instant>) -> Result<T, Failure<T>> {
+ // Optimistic preflight check (scheduling is expensive).
+ match self.try_recv() {
+ Err(Empty) => {}
+ data => return data,
+ }
+
+ // Welp, our channel has no data. Deschedule the current thread and
+ // initiate the blocking protocol.
+ let (wait_token, signal_token) = blocking::tokens();
+ if self.decrement(signal_token).is_ok() {
+ if let Some(deadline) = deadline {
+ let timed_out = !wait_token.wait_max_until(deadline);
+ if timed_out {
+ self.abort_selection(/* was_upgrade = */ false).map_err(Upgraded)?;
+ }
+ } else {
+ wait_token.wait();
+ }
+ }
+
+ match self.try_recv() {
+ // Messages which actually popped from the queue shouldn't count as
+ // a steal, so offset the decrement here (we already have our
+ // "steal" factored into the channel count above).
+ data @ (Ok(..) | Err(Upgraded(..))) => unsafe {
+ *self.queue.consumer_addition().steals.get() -= 1;
+ data
+ },
+
+ data => data,
+ }
+ }
+
+ pub fn try_recv(&self) -> Result<T, Failure<T>> {
+ match self.queue.pop() {
+ // If we stole some data, record to that effect (this will be
+ // factored into cnt later on).
+ //
+ // Note that we don't allow steals to grow without bound in order to
+ // prevent eventual overflow of either steals or cnt as an overflow
+ // would have catastrophic results. Sometimes, steals > cnt, but
+ // other times cnt > steals, so we don't know the relation between
+ // steals and cnt. This code path is executed only rarely, so we do
+ // a pretty slow operation, of swapping 0 into cnt, taking steals
+ // down as much as possible (without going negative), and then
+ // adding back in whatever we couldn't factor into steals.
+ Some(data) => unsafe {
+ if *self.queue.consumer_addition().steals.get() > MAX_STEALS {
+ match self.queue.producer_addition().cnt.swap(0, Ordering::SeqCst) {
+ DISCONNECTED => {
+ self.queue
+ .producer_addition()
+ .cnt
+ .store(DISCONNECTED, Ordering::SeqCst);
+ }
+ n => {
+ let m = cmp::min(n, *self.queue.consumer_addition().steals.get());
+ *self.queue.consumer_addition().steals.get() -= m;
+ self.bump(n - m);
+ }
+ }
+ assert!(*self.queue.consumer_addition().steals.get() >= 0);
+ }
+ *self.queue.consumer_addition().steals.get() += 1;
+ match data {
+ Data(t) => Ok(t),
+ GoUp(up) => Err(Upgraded(up)),
+ }
+ },
+
+ None => {
+ match self.queue.producer_addition().cnt.load(Ordering::SeqCst) {
+ n if n != DISCONNECTED => Err(Empty),
+
+ // This is a little bit of a tricky case. We failed to pop
+ // data above, and then we have viewed that the channel is
+ // disconnected. In this window more data could have been
+ // sent on the channel. It doesn't really make sense to
+ // return that the channel is disconnected when there's
+ // actually data on it, so be extra sure there's no data by
+ // popping one more time.
+ //
+ // We can ignore steals because the other end is
+ // disconnected and we'll never need to really factor in our
+ // steals again.
+ _ => match self.queue.pop() {
+ Some(Data(t)) => Ok(t),
+ Some(GoUp(up)) => Err(Upgraded(up)),
+ None => Err(Disconnected),
+ },
+ }
+ }
+ }
+ }
+
+ pub fn drop_chan(&self) {
+ // Dropping a channel is pretty simple, we just flag it as disconnected
+ // and then wakeup a blocker if there is one.
+ match self.queue.producer_addition().cnt.swap(DISCONNECTED, Ordering::SeqCst) {
+ -1 => {
+ self.take_to_wake().signal();
+ }
+ DISCONNECTED => {}
+ n => {
+ assert!(n >= 0);
+ }
+ }
+ }
+
+ pub fn drop_port(&self) {
+ // Dropping a port seems like a fairly trivial thing. In theory all we
+ // need to do is flag that we're disconnected and then everything else
+ // can take over (we don't have anyone to wake up).
+ //
+ // The catch for Ports is that we want to drop the entire contents of
+ // the queue. There are multiple reasons for having this property, the
+ // largest of which is that if another chan is waiting in this channel
+ // (but not received yet), then waiting on that port will cause a
+ // deadlock.
+ //
+ // So if we accept that we must now destroy the entire contents of the
+ // queue, this code may make a bit more sense. The tricky part is that
+ // we can't let any in-flight sends go un-dropped, we have to make sure
+ // *everything* is dropped and nothing new will come onto the channel.
+
+ // The first thing we do is set a flag saying that we're done for. All
+ // sends are gated on this flag, so we're immediately guaranteed that
+ // there are a bounded number of active sends that we'll have to deal
+ // with.
+ self.queue.producer_addition().port_dropped.store(true, Ordering::SeqCst);
+
+ // Now that we're guaranteed to deal with a bounded number of senders,
+ // we need to drain the queue. This draining process happens atomically
+ // with respect to the "count" of the channel. If the count is nonzero
+ // (with steals taken into account), then there must be data on the
+ // channel. In this case we drain everything and then try again. We will
+ // continue to fail while active senders send data while we're dropping
+ // data, but eventually we're guaranteed to break out of this loop
+ // (because there is a bounded number of senders).
+ let mut steals = unsafe { *self.queue.consumer_addition().steals.get() };
+ while {
+ match self.queue.producer_addition().cnt.compare_exchange(
+ steals,
+ DISCONNECTED,
+ Ordering::SeqCst,
+ Ordering::SeqCst,
+ ) {
+ Ok(_) => false,
+ Err(old) => old != DISCONNECTED,
+ }
+ } {
+ while self.queue.pop().is_some() {
+ steals += 1;
+ }
+ }
+
+ // At this point in time, we have gated all future senders from sending,
+ // and we have flagged the channel as being disconnected. The senders
+ // still have some responsibility, however, because some sends might not
+ // complete until after we flag the disconnection. There are more
+ // details in the sending methods that see DISCONNECTED
+ }
+
+ ////////////////////////////////////////////////////////////////////////////
+ // select implementation
+ ////////////////////////////////////////////////////////////////////////////
+
+ // increment the count on the channel (used for selection)
+ fn bump(&self, amt: isize) -> isize {
+ match self.queue.producer_addition().cnt.fetch_add(amt, Ordering::SeqCst) {
+ DISCONNECTED => {
+ self.queue.producer_addition().cnt.store(DISCONNECTED, Ordering::SeqCst);
+ DISCONNECTED
+ }
+ n => n,
+ }
+ }
+
+ // Removes a previous thread from being blocked in this port
+ pub fn abort_selection(&self, was_upgrade: bool) -> Result<bool, Receiver<T>> {
+ // If we're aborting selection after upgrading from a oneshot, then
+ // we're guarantee that no one is waiting. The only way that we could
+ // have seen the upgrade is if data was actually sent on the channel
+ // half again. For us, this means that there is guaranteed to be data on
+ // this channel. Furthermore, we're guaranteed that there was no
+ // start_selection previously, so there's no need to modify `self.cnt`
+ // at all.
+ //
+ // Hence, because of these invariants, we immediately return `Ok(true)`.
+ // Note that the data might not actually be sent on the channel just yet.
+ // The other end could have flagged the upgrade but not sent data to
+ // this end. This is fine because we know it's a small bounded windows
+ // of time until the data is actually sent.
+ if was_upgrade {
+ assert_eq!(unsafe { *self.queue.consumer_addition().steals.get() }, 0);
+ assert_eq!(self.queue.producer_addition().to_wake.load(Ordering::SeqCst), EMPTY);
+ return Ok(true);
+ }
+
+ // We want to make sure that the count on the channel goes non-negative,
+ // and in the stream case we can have at most one steal, so just assume
+ // that we had one steal.
+ let steals = 1;
+ let prev = self.bump(steals + 1);
+
+ // If we were previously disconnected, then we know for sure that there
+ // is no thread in to_wake, so just keep going
+ let has_data = if prev == DISCONNECTED {
+ assert_eq!(self.queue.producer_addition().to_wake.load(Ordering::SeqCst), EMPTY);
+ true // there is data, that data is that we're disconnected
+ } else {
+ let cur = prev + steals + 1;
+ assert!(cur >= 0);
+
+ // If the previous count was negative, then we just made things go
+ // positive, hence we passed the -1 boundary and we're responsible
+ // for removing the to_wake() field and trashing it.
+ //
+ // If the previous count was positive then we're in a tougher
+ // situation. A possible race is that a sender just incremented
+ // through -1 (meaning it's going to try to wake a thread up), but it
+ // hasn't yet read the to_wake. In order to prevent a future recv()
+ // from waking up too early (this sender picking up the plastered
+ // over to_wake), we spin loop here waiting for to_wake to be 0.
+ // Note that this entire select() implementation needs an overhaul,
+ // and this is *not* the worst part of it, so this is not done as a
+ // final solution but rather out of necessity for now to get
+ // something working.
+ if prev < 0 {
+ drop(self.take_to_wake());
+ } else {
+ while self.queue.producer_addition().to_wake.load(Ordering::SeqCst) != EMPTY {
+ thread::yield_now();
+ }
+ }
+ unsafe {
+ assert_eq!(*self.queue.consumer_addition().steals.get(), 0);
+ *self.queue.consumer_addition().steals.get() = steals;
+ }
+
+ // if we were previously positive, then there's surely data to
+ // receive
+ prev >= 0
+ };
+
+ // Now that we've determined that this queue "has data", we peek at the
+ // queue to see if the data is an upgrade or not. If it's an upgrade,
+ // then we need to destroy this port and abort selection on the
+ // upgraded port.
+ if has_data {
+ match self.queue.peek() {
+ Some(&mut GoUp(..)) => match self.queue.pop() {
+ Some(GoUp(port)) => Err(port),
+ _ => unreachable!(),
+ },
+ _ => Ok(true),
+ }
+ } else {
+ Ok(false)
+ }
+ }
+}
+
+impl<T> Drop for Packet<T> {
+ fn drop(&mut self) {
+ // Note that this load is not only an assert for correctness about
+ // disconnection, but also a proper fence before the read of
+ // `to_wake`, so this assert cannot be removed with also removing
+ // the `to_wake` assert.
+ assert_eq!(self.queue.producer_addition().cnt.load(Ordering::SeqCst), DISCONNECTED);
+ assert_eq!(self.queue.producer_addition().to_wake.load(Ordering::SeqCst), EMPTY);
+ }
+}
diff --git a/library/std/src/sync/mpsc/sync.rs b/library/std/src/sync/mpsc/sync.rs
new file mode 100644
index 000000000..733761671
--- /dev/null
+++ b/library/std/src/sync/mpsc/sync.rs
@@ -0,0 +1,495 @@
+use self::Blocker::*;
+/// Synchronous channels/ports
+///
+/// This channel implementation differs significantly from the asynchronous
+/// implementations found next to it (oneshot/stream/share). This is an
+/// implementation of a synchronous, bounded buffer channel.
+///
+/// Each channel is created with some amount of backing buffer, and sends will
+/// *block* until buffer space becomes available. A buffer size of 0 is valid,
+/// which means that every successful send is paired with a successful recv.
+///
+/// This flavor of channels defines a new `send_opt` method for channels which
+/// is the method by which a message is sent but the thread does not panic if it
+/// cannot be delivered.
+///
+/// Another major difference is that send() will *always* return back the data
+/// if it couldn't be sent. This is because it is deterministically known when
+/// the data is received and when it is not received.
+///
+/// Implementation-wise, it can all be summed up with "use a mutex plus some
+/// logic". The mutex used here is an OS native mutex, meaning that no user code
+/// is run inside of the mutex (to prevent context switching). This
+/// implementation shares almost all code for the buffered and unbuffered cases
+/// of a synchronous channel. There are a few branches for the unbuffered case,
+/// but they're mostly just relevant to blocking senders.
+pub use self::Failure::*;
+
+use core::intrinsics::abort;
+use core::mem;
+use core::ptr;
+
+use crate::sync::atomic::{AtomicUsize, Ordering};
+use crate::sync::mpsc::blocking::{self, SignalToken, WaitToken};
+use crate::sync::{Mutex, MutexGuard};
+use crate::time::Instant;
+
+const MAX_REFCOUNT: usize = (isize::MAX) as usize;
+
+pub struct Packet<T> {
+ /// Only field outside of the mutex. Just done for kicks, but mainly because
+ /// the other shared channel already had the code implemented
+ channels: AtomicUsize,
+
+ lock: Mutex<State<T>>,
+}
+
+unsafe impl<T: Send> Send for Packet<T> {}
+
+unsafe impl<T: Send> Sync for Packet<T> {}
+
+struct State<T> {
+ disconnected: bool, // Is the channel disconnected yet?
+ queue: Queue, // queue of senders waiting to send data
+ blocker: Blocker, // currently blocked thread on this channel
+ buf: Buffer<T>, // storage for buffered messages
+ cap: usize, // capacity of this channel
+
+ /// A curious flag used to indicate whether a sender failed or succeeded in
+ /// blocking. This is used to transmit information back to the thread that it
+ /// must dequeue its message from the buffer because it was not received.
+ /// This is only relevant in the 0-buffer case. This obviously cannot be
+ /// safely constructed, but it's guaranteed to always have a valid pointer
+ /// value.
+ canceled: Option<&'static mut bool>,
+}
+
+unsafe impl<T: Send> Send for State<T> {}
+
+/// Possible flavors of threads who can be blocked on this channel.
+enum Blocker {
+ BlockedSender(SignalToken),
+ BlockedReceiver(SignalToken),
+ NoneBlocked,
+}
+
+/// Simple queue for threading threads together. Nodes are stack-allocated, so
+/// this structure is not safe at all
+struct Queue {
+ head: *mut Node,
+ tail: *mut Node,
+}
+
+struct Node {
+ token: Option<SignalToken>,
+ next: *mut Node,
+}
+
+unsafe impl Send for Node {}
+
+/// A simple ring-buffer
+struct Buffer<T> {
+ buf: Vec<Option<T>>,
+ start: usize,
+ size: usize,
+}
+
+#[derive(Debug)]
+pub enum Failure {
+ Empty,
+ Disconnected,
+}
+
+/// Atomically blocks the current thread, placing it into `slot`, unlocking `lock`
+/// in the meantime. This re-locks the mutex upon returning.
+fn wait<'a, 'b, T>(
+ lock: &'a Mutex<State<T>>,
+ mut guard: MutexGuard<'b, State<T>>,
+ f: fn(SignalToken) -> Blocker,
+) -> MutexGuard<'a, State<T>> {
+ let (wait_token, signal_token) = blocking::tokens();
+ match mem::replace(&mut guard.blocker, f(signal_token)) {
+ NoneBlocked => {}
+ _ => unreachable!(),
+ }
+ drop(guard); // unlock
+ wait_token.wait(); // block
+ lock.lock().unwrap() // relock
+}
+
+/// Same as wait, but waiting at most until `deadline`.
+fn wait_timeout_receiver<'a, 'b, T>(
+ lock: &'a Mutex<State<T>>,
+ deadline: Instant,
+ mut guard: MutexGuard<'b, State<T>>,
+ success: &mut bool,
+) -> MutexGuard<'a, State<T>> {
+ let (wait_token, signal_token) = blocking::tokens();
+ match mem::replace(&mut guard.blocker, BlockedReceiver(signal_token)) {
+ NoneBlocked => {}
+ _ => unreachable!(),
+ }
+ drop(guard); // unlock
+ *success = wait_token.wait_max_until(deadline); // block
+ let mut new_guard = lock.lock().unwrap(); // relock
+ if !*success {
+ abort_selection(&mut new_guard);
+ }
+ new_guard
+}
+
+fn abort_selection<T>(guard: &mut MutexGuard<'_, State<T>>) -> bool {
+ match mem::replace(&mut guard.blocker, NoneBlocked) {
+ NoneBlocked => true,
+ BlockedSender(token) => {
+ guard.blocker = BlockedSender(token);
+ true
+ }
+ BlockedReceiver(token) => {
+ drop(token);
+ false
+ }
+ }
+}
+
+/// Wakes up a thread, dropping the lock at the correct time
+fn wakeup<T>(token: SignalToken, guard: MutexGuard<'_, State<T>>) {
+ // We need to be careful to wake up the waiting thread *outside* of the mutex
+ // in case it incurs a context switch.
+ drop(guard);
+ token.signal();
+}
+
+impl<T> Packet<T> {
+ pub fn new(capacity: usize) -> Packet<T> {
+ Packet {
+ channels: AtomicUsize::new(1),
+ lock: Mutex::new(State {
+ disconnected: false,
+ blocker: NoneBlocked,
+ cap: capacity,
+ canceled: None,
+ queue: Queue { head: ptr::null_mut(), tail: ptr::null_mut() },
+ buf: Buffer {
+ buf: (0..capacity + if capacity == 0 { 1 } else { 0 }).map(|_| None).collect(),
+ start: 0,
+ size: 0,
+ },
+ }),
+ }
+ }
+
+ // wait until a send slot is available, returning locked access to
+ // the channel state.
+ fn acquire_send_slot(&self) -> MutexGuard<'_, State<T>> {
+ let mut node = Node { token: None, next: ptr::null_mut() };
+ loop {
+ let mut guard = self.lock.lock().unwrap();
+ // are we ready to go?
+ if guard.disconnected || guard.buf.size() < guard.buf.capacity() {
+ return guard;
+ }
+ // no room; actually block
+ let wait_token = guard.queue.enqueue(&mut node);
+ drop(guard);
+ wait_token.wait();
+ }
+ }
+
+ pub fn send(&self, t: T) -> Result<(), T> {
+ let mut guard = self.acquire_send_slot();
+ if guard.disconnected {
+ return Err(t);
+ }
+ guard.buf.enqueue(t);
+
+ match mem::replace(&mut guard.blocker, NoneBlocked) {
+ // if our capacity is 0, then we need to wait for a receiver to be
+ // available to take our data. After waiting, we check again to make
+ // sure the port didn't go away in the meantime. If it did, we need
+ // to hand back our data.
+ NoneBlocked if guard.cap == 0 => {
+ let mut canceled = false;
+ assert!(guard.canceled.is_none());
+ guard.canceled = Some(unsafe { mem::transmute(&mut canceled) });
+ let mut guard = wait(&self.lock, guard, BlockedSender);
+ if canceled { Err(guard.buf.dequeue()) } else { Ok(()) }
+ }
+
+ // success, we buffered some data
+ NoneBlocked => Ok(()),
+
+ // success, someone's about to receive our buffered data.
+ BlockedReceiver(token) => {
+ wakeup(token, guard);
+ Ok(())
+ }
+
+ BlockedSender(..) => panic!("lolwut"),
+ }
+ }
+
+ pub fn try_send(&self, t: T) -> Result<(), super::TrySendError<T>> {
+ let mut guard = self.lock.lock().unwrap();
+ if guard.disconnected {
+ Err(super::TrySendError::Disconnected(t))
+ } else if guard.buf.size() == guard.buf.capacity() {
+ Err(super::TrySendError::Full(t))
+ } else if guard.cap == 0 {
+ // With capacity 0, even though we have buffer space we can't
+ // transfer the data unless there's a receiver waiting.
+ match mem::replace(&mut guard.blocker, NoneBlocked) {
+ NoneBlocked => Err(super::TrySendError::Full(t)),
+ BlockedSender(..) => unreachable!(),
+ BlockedReceiver(token) => {
+ guard.buf.enqueue(t);
+ wakeup(token, guard);
+ Ok(())
+ }
+ }
+ } else {
+ // If the buffer has some space and the capacity isn't 0, then we
+ // just enqueue the data for later retrieval, ensuring to wake up
+ // any blocked receiver if there is one.
+ assert!(guard.buf.size() < guard.buf.capacity());
+ guard.buf.enqueue(t);
+ match mem::replace(&mut guard.blocker, NoneBlocked) {
+ BlockedReceiver(token) => wakeup(token, guard),
+ NoneBlocked => {}
+ BlockedSender(..) => unreachable!(),
+ }
+ Ok(())
+ }
+ }
+
+ // Receives a message from this channel
+ //
+ // When reading this, remember that there can only ever be one receiver at
+ // time.
+ pub fn recv(&self, deadline: Option<Instant>) -> Result<T, Failure> {
+ let mut guard = self.lock.lock().unwrap();
+
+ let mut woke_up_after_waiting = false;
+ // Wait for the buffer to have something in it. No need for a
+ // while loop because we're the only receiver.
+ if !guard.disconnected && guard.buf.size() == 0 {
+ if let Some(deadline) = deadline {
+ guard =
+ wait_timeout_receiver(&self.lock, deadline, guard, &mut woke_up_after_waiting);
+ } else {
+ guard = wait(&self.lock, guard, BlockedReceiver);
+ woke_up_after_waiting = true;
+ }
+ }
+
+ // N.B., channel could be disconnected while waiting, so the order of
+ // these conditionals is important.
+ if guard.disconnected && guard.buf.size() == 0 {
+ return Err(Disconnected);
+ }
+
+ // Pick up the data, wake up our neighbors, and carry on
+ assert!(guard.buf.size() > 0 || (deadline.is_some() && !woke_up_after_waiting));
+
+ if guard.buf.size() == 0 {
+ return Err(Empty);
+ }
+
+ let ret = guard.buf.dequeue();
+ self.wakeup_senders(woke_up_after_waiting, guard);
+ Ok(ret)
+ }
+
+ pub fn try_recv(&self) -> Result<T, Failure> {
+ let mut guard = self.lock.lock().unwrap();
+
+ // Easy cases first
+ if guard.disconnected && guard.buf.size() == 0 {
+ return Err(Disconnected);
+ }
+ if guard.buf.size() == 0 {
+ return Err(Empty);
+ }
+
+ // Be sure to wake up neighbors
+ let ret = Ok(guard.buf.dequeue());
+ self.wakeup_senders(false, guard);
+ ret
+ }
+
+ // Wake up pending senders after some data has been received
+ //
+ // * `waited` - flag if the receiver blocked to receive some data, or if it
+ // just picked up some data on the way out
+ // * `guard` - the lock guard that is held over this channel's lock
+ fn wakeup_senders(&self, waited: bool, mut guard: MutexGuard<'_, State<T>>) {
+ let pending_sender1: Option<SignalToken> = guard.queue.dequeue();
+
+ // If this is a no-buffer channel (cap == 0), then if we didn't wait we
+ // need to ACK the sender. If we waited, then the sender waking us up
+ // was already the ACK.
+ let pending_sender2 = if guard.cap == 0 && !waited {
+ match mem::replace(&mut guard.blocker, NoneBlocked) {
+ NoneBlocked => None,
+ BlockedReceiver(..) => unreachable!(),
+ BlockedSender(token) => {
+ guard.canceled.take();
+ Some(token)
+ }
+ }
+ } else {
+ None
+ };
+ mem::drop(guard);
+
+ // only outside of the lock do we wake up the pending threads
+ if let Some(token) = pending_sender1 {
+ token.signal();
+ }
+ if let Some(token) = pending_sender2 {
+ token.signal();
+ }
+ }
+
+ // Prepares this shared packet for a channel clone, essentially just bumping
+ // a refcount.
+ pub fn clone_chan(&self) {
+ let old_count = self.channels.fetch_add(1, Ordering::SeqCst);
+
+ // See comments on Arc::clone() on why we do this (for `mem::forget`).
+ if old_count > MAX_REFCOUNT {
+ abort();
+ }
+ }
+
+ pub fn drop_chan(&self) {
+ // Only flag the channel as disconnected if we're the last channel
+ match self.channels.fetch_sub(1, Ordering::SeqCst) {
+ 1 => {}
+ _ => return,
+ }
+
+ // Not much to do other than wake up a receiver if one's there
+ let mut guard = self.lock.lock().unwrap();
+ if guard.disconnected {
+ return;
+ }
+ guard.disconnected = true;
+ match mem::replace(&mut guard.blocker, NoneBlocked) {
+ NoneBlocked => {}
+ BlockedSender(..) => unreachable!(),
+ BlockedReceiver(token) => wakeup(token, guard),
+ }
+ }
+
+ pub fn drop_port(&self) {
+ let mut guard = self.lock.lock().unwrap();
+
+ if guard.disconnected {
+ return;
+ }
+ guard.disconnected = true;
+
+ // If the capacity is 0, then the sender may want its data back after
+ // we're disconnected. Otherwise it's now our responsibility to destroy
+ // the buffered data. As with many other portions of this code, this
+ // needs to be careful to destroy the data *outside* of the lock to
+ // prevent deadlock.
+ let _data = if guard.cap != 0 { mem::take(&mut guard.buf.buf) } else { Vec::new() };
+ let mut queue =
+ mem::replace(&mut guard.queue, Queue { head: ptr::null_mut(), tail: ptr::null_mut() });
+
+ let waiter = match mem::replace(&mut guard.blocker, NoneBlocked) {
+ NoneBlocked => None,
+ BlockedSender(token) => {
+ *guard.canceled.take().unwrap() = true;
+ Some(token)
+ }
+ BlockedReceiver(..) => unreachable!(),
+ };
+ mem::drop(guard);
+
+ while let Some(token) = queue.dequeue() {
+ token.signal();
+ }
+ if let Some(token) = waiter {
+ token.signal();
+ }
+ }
+}
+
+impl<T> Drop for Packet<T> {
+ fn drop(&mut self) {
+ assert_eq!(self.channels.load(Ordering::SeqCst), 0);
+ let mut guard = self.lock.lock().unwrap();
+ assert!(guard.queue.dequeue().is_none());
+ assert!(guard.canceled.is_none());
+ }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+// Buffer, a simple ring buffer backed by Vec<T>
+////////////////////////////////////////////////////////////////////////////////
+
+impl<T> Buffer<T> {
+ fn enqueue(&mut self, t: T) {
+ let pos = (self.start + self.size) % self.buf.len();
+ self.size += 1;
+ let prev = mem::replace(&mut self.buf[pos], Some(t));
+ assert!(prev.is_none());
+ }
+
+ fn dequeue(&mut self) -> T {
+ let start = self.start;
+ self.size -= 1;
+ self.start = (self.start + 1) % self.buf.len();
+ let result = &mut self.buf[start];
+ result.take().unwrap()
+ }
+
+ fn size(&self) -> usize {
+ self.size
+ }
+ fn capacity(&self) -> usize {
+ self.buf.len()
+ }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+// Queue, a simple queue to enqueue threads with (stack-allocated nodes)
+////////////////////////////////////////////////////////////////////////////////
+
+impl Queue {
+ fn enqueue(&mut self, node: &mut Node) -> WaitToken {
+ let (wait_token, signal_token) = blocking::tokens();
+ node.token = Some(signal_token);
+ node.next = ptr::null_mut();
+
+ if self.tail.is_null() {
+ self.head = node as *mut Node;
+ self.tail = node as *mut Node;
+ } else {
+ unsafe {
+ (*self.tail).next = node as *mut Node;
+ self.tail = node as *mut Node;
+ }
+ }
+
+ wait_token
+ }
+
+ fn dequeue(&mut self) -> Option<SignalToken> {
+ if self.head.is_null() {
+ return None;
+ }
+ let node = self.head;
+ self.head = unsafe { (*node).next };
+ if self.head.is_null() {
+ self.tail = ptr::null_mut();
+ }
+ unsafe {
+ (*node).next = ptr::null_mut();
+ Some((*node).token.take().unwrap())
+ }
+ }
+}
diff --git a/library/std/src/sync/mpsc/sync_tests.rs b/library/std/src/sync/mpsc/sync_tests.rs
new file mode 100644
index 000000000..e58649bab
--- /dev/null
+++ b/library/std/src/sync/mpsc/sync_tests.rs
@@ -0,0 +1,647 @@
+use super::*;
+use crate::env;
+use crate::thread;
+use crate::time::Duration;
+
+pub fn stress_factor() -> usize {
+ match env::var("RUST_TEST_STRESS") {
+ Ok(val) => val.parse().unwrap(),
+ Err(..) => 1,
+ }
+}
+
+#[test]
+fn smoke() {
+ let (tx, rx) = sync_channel::<i32>(1);
+ tx.send(1).unwrap();
+ assert_eq!(rx.recv().unwrap(), 1);
+}
+
+#[test]
+fn drop_full() {
+ let (tx, _rx) = sync_channel::<Box<isize>>(1);
+ tx.send(Box::new(1)).unwrap();
+}
+
+#[test]
+fn smoke_shared() {
+ let (tx, rx) = sync_channel::<i32>(1);
+ tx.send(1).unwrap();
+ assert_eq!(rx.recv().unwrap(), 1);
+ let tx = tx.clone();
+ tx.send(1).unwrap();
+ assert_eq!(rx.recv().unwrap(), 1);
+}
+
+#[test]
+fn recv_timeout() {
+ let (tx, rx) = sync_channel::<i32>(1);
+ assert_eq!(rx.recv_timeout(Duration::from_millis(1)), Err(RecvTimeoutError::Timeout));
+ tx.send(1).unwrap();
+ assert_eq!(rx.recv_timeout(Duration::from_millis(1)), Ok(1));
+}
+
+#[test]
+fn smoke_threads() {
+ let (tx, rx) = sync_channel::<i32>(0);
+ let _t = thread::spawn(move || {
+ tx.send(1).unwrap();
+ });
+ assert_eq!(rx.recv().unwrap(), 1);
+}
+
+#[test]
+fn smoke_port_gone() {
+ let (tx, rx) = sync_channel::<i32>(0);
+ drop(rx);
+ assert!(tx.send(1).is_err());
+}
+
+#[test]
+fn smoke_shared_port_gone2() {
+ let (tx, rx) = sync_channel::<i32>(0);
+ drop(rx);
+ let tx2 = tx.clone();
+ drop(tx);
+ assert!(tx2.send(1).is_err());
+}
+
+#[test]
+fn port_gone_concurrent() {
+ let (tx, rx) = sync_channel::<i32>(0);
+ let _t = thread::spawn(move || {
+ rx.recv().unwrap();
+ });
+ while tx.send(1).is_ok() {}
+}
+
+#[test]
+fn port_gone_concurrent_shared() {
+ let (tx, rx) = sync_channel::<i32>(0);
+ let tx2 = tx.clone();
+ let _t = thread::spawn(move || {
+ rx.recv().unwrap();
+ });
+ while tx.send(1).is_ok() && tx2.send(1).is_ok() {}
+}
+
+#[test]
+fn smoke_chan_gone() {
+ let (tx, rx) = sync_channel::<i32>(0);
+ drop(tx);
+ assert!(rx.recv().is_err());
+}
+
+#[test]
+fn smoke_chan_gone_shared() {
+ let (tx, rx) = sync_channel::<()>(0);
+ let tx2 = tx.clone();
+ drop(tx);
+ drop(tx2);
+ assert!(rx.recv().is_err());
+}
+
+#[test]
+fn chan_gone_concurrent() {
+ let (tx, rx) = sync_channel::<i32>(0);
+ thread::spawn(move || {
+ tx.send(1).unwrap();
+ tx.send(1).unwrap();
+ });
+ while rx.recv().is_ok() {}
+}
+
+#[test]
+fn stress() {
+ let (tx, rx) = sync_channel::<i32>(0);
+ thread::spawn(move || {
+ for _ in 0..10000 {
+ tx.send(1).unwrap();
+ }
+ });
+ for _ in 0..10000 {
+ assert_eq!(rx.recv().unwrap(), 1);
+ }
+}
+
+#[test]
+fn stress_recv_timeout_two_threads() {
+ let (tx, rx) = sync_channel::<i32>(0);
+
+ thread::spawn(move || {
+ for _ in 0..10000 {
+ tx.send(1).unwrap();
+ }
+ });
+
+ let mut recv_count = 0;
+ loop {
+ match rx.recv_timeout(Duration::from_millis(1)) {
+ Ok(v) => {
+ assert_eq!(v, 1);
+ recv_count += 1;
+ }
+ Err(RecvTimeoutError::Timeout) => continue,
+ Err(RecvTimeoutError::Disconnected) => break,
+ }
+ }
+
+ assert_eq!(recv_count, 10000);
+}
+
+#[test]
+fn stress_recv_timeout_shared() {
+ const AMT: u32 = 1000;
+ const NTHREADS: u32 = 8;
+ let (tx, rx) = sync_channel::<i32>(0);
+ let (dtx, drx) = sync_channel::<()>(0);
+
+ thread::spawn(move || {
+ let mut recv_count = 0;
+ loop {
+ match rx.recv_timeout(Duration::from_millis(10)) {
+ Ok(v) => {
+ assert_eq!(v, 1);
+ recv_count += 1;
+ }
+ Err(RecvTimeoutError::Timeout) => continue,
+ Err(RecvTimeoutError::Disconnected) => break,
+ }
+ }
+
+ assert_eq!(recv_count, AMT * NTHREADS);
+ assert!(rx.try_recv().is_err());
+
+ dtx.send(()).unwrap();
+ });
+
+ for _ in 0..NTHREADS {
+ let tx = tx.clone();
+ thread::spawn(move || {
+ for _ in 0..AMT {
+ tx.send(1).unwrap();
+ }
+ });
+ }
+
+ drop(tx);
+
+ drx.recv().unwrap();
+}
+
+#[test]
+fn stress_shared() {
+ const AMT: u32 = 1000;
+ const NTHREADS: u32 = 8;
+ let (tx, rx) = sync_channel::<i32>(0);
+ let (dtx, drx) = sync_channel::<()>(0);
+
+ thread::spawn(move || {
+ for _ in 0..AMT * NTHREADS {
+ assert_eq!(rx.recv().unwrap(), 1);
+ }
+ match rx.try_recv() {
+ Ok(..) => panic!(),
+ _ => {}
+ }
+ dtx.send(()).unwrap();
+ });
+
+ for _ in 0..NTHREADS {
+ let tx = tx.clone();
+ thread::spawn(move || {
+ for _ in 0..AMT {
+ tx.send(1).unwrap();
+ }
+ });
+ }
+ drop(tx);
+ drx.recv().unwrap();
+}
+
+#[test]
+fn oneshot_single_thread_close_port_first() {
+ // Simple test of closing without sending
+ let (_tx, rx) = sync_channel::<i32>(0);
+ drop(rx);
+}
+
+#[test]
+fn oneshot_single_thread_close_chan_first() {
+ // Simple test of closing without sending
+ let (tx, _rx) = sync_channel::<i32>(0);
+ drop(tx);
+}
+
+#[test]
+fn oneshot_single_thread_send_port_close() {
+ // Testing that the sender cleans up the payload if receiver is closed
+ let (tx, rx) = sync_channel::<Box<i32>>(0);
+ drop(rx);
+ assert!(tx.send(Box::new(0)).is_err());
+}
+
+#[test]
+fn oneshot_single_thread_recv_chan_close() {
+ // Receiving on a closed chan will panic
+ let res = thread::spawn(move || {
+ let (tx, rx) = sync_channel::<i32>(0);
+ drop(tx);
+ rx.recv().unwrap();
+ })
+ .join();
+ // What is our res?
+ assert!(res.is_err());
+}
+
+#[test]
+fn oneshot_single_thread_send_then_recv() {
+ let (tx, rx) = sync_channel::<Box<i32>>(1);
+ tx.send(Box::new(10)).unwrap();
+ assert!(*rx.recv().unwrap() == 10);
+}
+
+#[test]
+fn oneshot_single_thread_try_send_open() {
+ let (tx, rx) = sync_channel::<i32>(1);
+ assert_eq!(tx.try_send(10), Ok(()));
+ assert!(rx.recv().unwrap() == 10);
+}
+
+#[test]
+fn oneshot_single_thread_try_send_closed() {
+ let (tx, rx) = sync_channel::<i32>(0);
+ drop(rx);
+ assert_eq!(tx.try_send(10), Err(TrySendError::Disconnected(10)));
+}
+
+#[test]
+fn oneshot_single_thread_try_send_closed2() {
+ let (tx, _rx) = sync_channel::<i32>(0);
+ assert_eq!(tx.try_send(10), Err(TrySendError::Full(10)));
+}
+
+#[test]
+fn oneshot_single_thread_try_recv_open() {
+ let (tx, rx) = sync_channel::<i32>(1);
+ tx.send(10).unwrap();
+ assert!(rx.recv() == Ok(10));
+}
+
+#[test]
+fn oneshot_single_thread_try_recv_closed() {
+ let (tx, rx) = sync_channel::<i32>(0);
+ drop(tx);
+ assert!(rx.recv().is_err());
+}
+
+#[test]
+fn oneshot_single_thread_try_recv_closed_with_data() {
+ let (tx, rx) = sync_channel::<i32>(1);
+ tx.send(10).unwrap();
+ drop(tx);
+ assert_eq!(rx.try_recv(), Ok(10));
+ assert_eq!(rx.try_recv(), Err(TryRecvError::Disconnected));
+}
+
+#[test]
+fn oneshot_single_thread_peek_data() {
+ let (tx, rx) = sync_channel::<i32>(1);
+ assert_eq!(rx.try_recv(), Err(TryRecvError::Empty));
+ tx.send(10).unwrap();
+ assert_eq!(rx.try_recv(), Ok(10));
+}
+
+#[test]
+fn oneshot_single_thread_peek_close() {
+ let (tx, rx) = sync_channel::<i32>(0);
+ drop(tx);
+ assert_eq!(rx.try_recv(), Err(TryRecvError::Disconnected));
+ assert_eq!(rx.try_recv(), Err(TryRecvError::Disconnected));
+}
+
+#[test]
+fn oneshot_single_thread_peek_open() {
+ let (_tx, rx) = sync_channel::<i32>(0);
+ assert_eq!(rx.try_recv(), Err(TryRecvError::Empty));
+}
+
+#[test]
+fn oneshot_multi_task_recv_then_send() {
+ let (tx, rx) = sync_channel::<Box<i32>>(0);
+ let _t = thread::spawn(move || {
+ assert!(*rx.recv().unwrap() == 10);
+ });
+
+ tx.send(Box::new(10)).unwrap();
+}
+
+#[test]
+fn oneshot_multi_task_recv_then_close() {
+ let (tx, rx) = sync_channel::<Box<i32>>(0);
+ let _t = thread::spawn(move || {
+ drop(tx);
+ });
+ let res = thread::spawn(move || {
+ assert!(*rx.recv().unwrap() == 10);
+ })
+ .join();
+ assert!(res.is_err());
+}
+
+#[test]
+fn oneshot_multi_thread_close_stress() {
+ for _ in 0..stress_factor() {
+ let (tx, rx) = sync_channel::<i32>(0);
+ let _t = thread::spawn(move || {
+ drop(rx);
+ });
+ drop(tx);
+ }
+}
+
+#[test]
+fn oneshot_multi_thread_send_close_stress() {
+ for _ in 0..stress_factor() {
+ let (tx, rx) = sync_channel::<i32>(0);
+ let _t = thread::spawn(move || {
+ drop(rx);
+ });
+ let _ = thread::spawn(move || {
+ tx.send(1).unwrap();
+ })
+ .join();
+ }
+}
+
+#[test]
+fn oneshot_multi_thread_recv_close_stress() {
+ for _ in 0..stress_factor() {
+ let (tx, rx) = sync_channel::<i32>(0);
+ let _t = thread::spawn(move || {
+ let res = thread::spawn(move || {
+ rx.recv().unwrap();
+ })
+ .join();
+ assert!(res.is_err());
+ });
+ let _t = thread::spawn(move || {
+ thread::spawn(move || {
+ drop(tx);
+ });
+ });
+ }
+}
+
+#[test]
+fn oneshot_multi_thread_send_recv_stress() {
+ for _ in 0..stress_factor() {
+ let (tx, rx) = sync_channel::<Box<i32>>(0);
+ let _t = thread::spawn(move || {
+ tx.send(Box::new(10)).unwrap();
+ });
+ assert!(*rx.recv().unwrap() == 10);
+ }
+}
+
+#[test]
+fn stream_send_recv_stress() {
+ for _ in 0..stress_factor() {
+ let (tx, rx) = sync_channel::<Box<i32>>(0);
+
+ send(tx, 0);
+ recv(rx, 0);
+
+ fn send(tx: SyncSender<Box<i32>>, i: i32) {
+ if i == 10 {
+ return;
+ }
+
+ thread::spawn(move || {
+ tx.send(Box::new(i)).unwrap();
+ send(tx, i + 1);
+ });
+ }
+
+ fn recv(rx: Receiver<Box<i32>>, i: i32) {
+ if i == 10 {
+ return;
+ }
+
+ thread::spawn(move || {
+ assert!(*rx.recv().unwrap() == i);
+ recv(rx, i + 1);
+ });
+ }
+ }
+}
+
+#[test]
+fn recv_a_lot() {
+ // Regression test that we don't run out of stack in scheduler context
+ let (tx, rx) = sync_channel(10000);
+ for _ in 0..10000 {
+ tx.send(()).unwrap();
+ }
+ for _ in 0..10000 {
+ rx.recv().unwrap();
+ }
+}
+
+#[test]
+fn shared_chan_stress() {
+ let (tx, rx) = sync_channel(0);
+ let total = stress_factor() + 100;
+ for _ in 0..total {
+ let tx = tx.clone();
+ thread::spawn(move || {
+ tx.send(()).unwrap();
+ });
+ }
+
+ for _ in 0..total {
+ rx.recv().unwrap();
+ }
+}
+
+#[test]
+fn test_nested_recv_iter() {
+ let (tx, rx) = sync_channel::<i32>(0);
+ let (total_tx, total_rx) = sync_channel::<i32>(0);
+
+ let _t = thread::spawn(move || {
+ let mut acc = 0;
+ for x in rx.iter() {
+ acc += x;
+ }
+ total_tx.send(acc).unwrap();
+ });
+
+ tx.send(3).unwrap();
+ tx.send(1).unwrap();
+ tx.send(2).unwrap();
+ drop(tx);
+ assert_eq!(total_rx.recv().unwrap(), 6);
+}
+
+#[test]
+fn test_recv_iter_break() {
+ let (tx, rx) = sync_channel::<i32>(0);
+ let (count_tx, count_rx) = sync_channel(0);
+
+ let _t = thread::spawn(move || {
+ let mut count = 0;
+ for x in rx.iter() {
+ if count >= 3 {
+ break;
+ } else {
+ count += x;
+ }
+ }
+ count_tx.send(count).unwrap();
+ });
+
+ tx.send(2).unwrap();
+ tx.send(2).unwrap();
+ tx.send(2).unwrap();
+ let _ = tx.try_send(2);
+ drop(tx);
+ assert_eq!(count_rx.recv().unwrap(), 4);
+}
+
+#[test]
+fn try_recv_states() {
+ let (tx1, rx1) = sync_channel::<i32>(1);
+ let (tx2, rx2) = sync_channel::<()>(1);
+ let (tx3, rx3) = sync_channel::<()>(1);
+ let _t = thread::spawn(move || {
+ rx2.recv().unwrap();
+ tx1.send(1).unwrap();
+ tx3.send(()).unwrap();
+ rx2.recv().unwrap();
+ drop(tx1);
+ tx3.send(()).unwrap();
+ });
+
+ assert_eq!(rx1.try_recv(), Err(TryRecvError::Empty));
+ tx2.send(()).unwrap();
+ rx3.recv().unwrap();
+ assert_eq!(rx1.try_recv(), Ok(1));
+ assert_eq!(rx1.try_recv(), Err(TryRecvError::Empty));
+ tx2.send(()).unwrap();
+ rx3.recv().unwrap();
+ assert_eq!(rx1.try_recv(), Err(TryRecvError::Disconnected));
+}
+
+// This bug used to end up in a livelock inside of the Receiver destructor
+// because the internal state of the Shared packet was corrupted
+#[test]
+fn destroy_upgraded_shared_port_when_sender_still_active() {
+ let (tx, rx) = sync_channel::<()>(0);
+ let (tx2, rx2) = sync_channel::<()>(0);
+ let _t = thread::spawn(move || {
+ rx.recv().unwrap(); // wait on a oneshot
+ drop(rx); // destroy a shared
+ tx2.send(()).unwrap();
+ });
+ // make sure the other thread has gone to sleep
+ for _ in 0..5000 {
+ thread::yield_now();
+ }
+
+ // upgrade to a shared chan and send a message
+ let t = tx.clone();
+ drop(tx);
+ t.send(()).unwrap();
+
+ // wait for the child thread to exit before we exit
+ rx2.recv().unwrap();
+}
+
+#[test]
+fn send1() {
+ let (tx, rx) = sync_channel::<i32>(0);
+ let _t = thread::spawn(move || {
+ rx.recv().unwrap();
+ });
+ assert_eq!(tx.send(1), Ok(()));
+}
+
+#[test]
+fn send2() {
+ let (tx, rx) = sync_channel::<i32>(0);
+ let _t = thread::spawn(move || {
+ drop(rx);
+ });
+ assert!(tx.send(1).is_err());
+}
+
+#[test]
+fn send3() {
+ let (tx, rx) = sync_channel::<i32>(1);
+ assert_eq!(tx.send(1), Ok(()));
+ let _t = thread::spawn(move || {
+ drop(rx);
+ });
+ assert!(tx.send(1).is_err());
+}
+
+#[test]
+fn send4() {
+ let (tx, rx) = sync_channel::<i32>(0);
+ let tx2 = tx.clone();
+ let (done, donerx) = channel();
+ let done2 = done.clone();
+ let _t = thread::spawn(move || {
+ assert!(tx.send(1).is_err());
+ done.send(()).unwrap();
+ });
+ let _t = thread::spawn(move || {
+ assert!(tx2.send(2).is_err());
+ done2.send(()).unwrap();
+ });
+ drop(rx);
+ donerx.recv().unwrap();
+ donerx.recv().unwrap();
+}
+
+#[test]
+fn try_send1() {
+ let (tx, _rx) = sync_channel::<i32>(0);
+ assert_eq!(tx.try_send(1), Err(TrySendError::Full(1)));
+}
+
+#[test]
+fn try_send2() {
+ let (tx, _rx) = sync_channel::<i32>(1);
+ assert_eq!(tx.try_send(1), Ok(()));
+ assert_eq!(tx.try_send(1), Err(TrySendError::Full(1)));
+}
+
+#[test]
+fn try_send3() {
+ let (tx, rx) = sync_channel::<i32>(1);
+ assert_eq!(tx.try_send(1), Ok(()));
+ drop(rx);
+ assert_eq!(tx.try_send(1), Err(TrySendError::Disconnected(1)));
+}
+
+#[test]
+fn issue_15761() {
+ fn repro() {
+ let (tx1, rx1) = sync_channel::<()>(3);
+ let (tx2, rx2) = sync_channel::<()>(3);
+
+ let _t = thread::spawn(move || {
+ rx1.recv().unwrap();
+ tx2.try_send(()).unwrap();
+ });
+
+ tx1.try_send(()).unwrap();
+ rx2.recv().unwrap();
+ }
+
+ for _ in 0..100 {
+ repro()
+ }
+}
diff --git a/library/std/src/sync/mpsc/tests.rs b/library/std/src/sync/mpsc/tests.rs
new file mode 100644
index 000000000..4deb3e596
--- /dev/null
+++ b/library/std/src/sync/mpsc/tests.rs
@@ -0,0 +1,706 @@
+use super::*;
+use crate::env;
+use crate::thread;
+use crate::time::{Duration, Instant};
+
+pub fn stress_factor() -> usize {
+ match env::var("RUST_TEST_STRESS") {
+ Ok(val) => val.parse().unwrap(),
+ Err(..) => 1,
+ }
+}
+
+#[test]
+fn smoke() {
+ let (tx, rx) = channel::<i32>();
+ tx.send(1).unwrap();
+ assert_eq!(rx.recv().unwrap(), 1);
+}
+
+#[test]
+fn drop_full() {
+ let (tx, _rx) = channel::<Box<isize>>();
+ tx.send(Box::new(1)).unwrap();
+}
+
+#[test]
+fn drop_full_shared() {
+ let (tx, _rx) = channel::<Box<isize>>();
+ drop(tx.clone());
+ drop(tx.clone());
+ tx.send(Box::new(1)).unwrap();
+}
+
+#[test]
+fn smoke_shared() {
+ let (tx, rx) = channel::<i32>();
+ tx.send(1).unwrap();
+ assert_eq!(rx.recv().unwrap(), 1);
+ let tx = tx.clone();
+ tx.send(1).unwrap();
+ assert_eq!(rx.recv().unwrap(), 1);
+}
+
+#[test]
+fn smoke_threads() {
+ let (tx, rx) = channel::<i32>();
+ let _t = thread::spawn(move || {
+ tx.send(1).unwrap();
+ });
+ assert_eq!(rx.recv().unwrap(), 1);
+}
+
+#[test]
+fn smoke_port_gone() {
+ let (tx, rx) = channel::<i32>();
+ drop(rx);
+ assert!(tx.send(1).is_err());
+}
+
+#[test]
+fn smoke_shared_port_gone() {
+ let (tx, rx) = channel::<i32>();
+ drop(rx);
+ assert!(tx.send(1).is_err())
+}
+
+#[test]
+fn smoke_shared_port_gone2() {
+ let (tx, rx) = channel::<i32>();
+ drop(rx);
+ let tx2 = tx.clone();
+ drop(tx);
+ assert!(tx2.send(1).is_err());
+}
+
+#[test]
+fn port_gone_concurrent() {
+ let (tx, rx) = channel::<i32>();
+ let _t = thread::spawn(move || {
+ rx.recv().unwrap();
+ });
+ while tx.send(1).is_ok() {}
+}
+
+#[test]
+fn port_gone_concurrent_shared() {
+ let (tx, rx) = channel::<i32>();
+ let tx2 = tx.clone();
+ let _t = thread::spawn(move || {
+ rx.recv().unwrap();
+ });
+ while tx.send(1).is_ok() && tx2.send(1).is_ok() {}
+}
+
+#[test]
+fn smoke_chan_gone() {
+ let (tx, rx) = channel::<i32>();
+ drop(tx);
+ assert!(rx.recv().is_err());
+}
+
+#[test]
+fn smoke_chan_gone_shared() {
+ let (tx, rx) = channel::<()>();
+ let tx2 = tx.clone();
+ drop(tx);
+ drop(tx2);
+ assert!(rx.recv().is_err());
+}
+
+#[test]
+fn chan_gone_concurrent() {
+ let (tx, rx) = channel::<i32>();
+ let _t = thread::spawn(move || {
+ tx.send(1).unwrap();
+ tx.send(1).unwrap();
+ });
+ while rx.recv().is_ok() {}
+}
+
+#[test]
+fn stress() {
+ let (tx, rx) = channel::<i32>();
+ let t = thread::spawn(move || {
+ for _ in 0..10000 {
+ tx.send(1).unwrap();
+ }
+ });
+ for _ in 0..10000 {
+ assert_eq!(rx.recv().unwrap(), 1);
+ }
+ t.join().ok().expect("thread panicked");
+}
+
+#[test]
+fn stress_shared() {
+ const AMT: u32 = 10000;
+ const NTHREADS: u32 = 8;
+ let (tx, rx) = channel::<i32>();
+
+ let t = thread::spawn(move || {
+ for _ in 0..AMT * NTHREADS {
+ assert_eq!(rx.recv().unwrap(), 1);
+ }
+ match rx.try_recv() {
+ Ok(..) => panic!(),
+ _ => {}
+ }
+ });
+
+ for _ in 0..NTHREADS {
+ let tx = tx.clone();
+ thread::spawn(move || {
+ for _ in 0..AMT {
+ tx.send(1).unwrap();
+ }
+ });
+ }
+ drop(tx);
+ t.join().ok().expect("thread panicked");
+}
+
+#[test]
+fn send_from_outside_runtime() {
+ let (tx1, rx1) = channel::<()>();
+ let (tx2, rx2) = channel::<i32>();
+ let t1 = thread::spawn(move || {
+ tx1.send(()).unwrap();
+ for _ in 0..40 {
+ assert_eq!(rx2.recv().unwrap(), 1);
+ }
+ });
+ rx1.recv().unwrap();
+ let t2 = thread::spawn(move || {
+ for _ in 0..40 {
+ tx2.send(1).unwrap();
+ }
+ });
+ t1.join().ok().expect("thread panicked");
+ t2.join().ok().expect("thread panicked");
+}
+
+#[test]
+fn recv_from_outside_runtime() {
+ let (tx, rx) = channel::<i32>();
+ let t = thread::spawn(move || {
+ for _ in 0..40 {
+ assert_eq!(rx.recv().unwrap(), 1);
+ }
+ });
+ for _ in 0..40 {
+ tx.send(1).unwrap();
+ }
+ t.join().ok().expect("thread panicked");
+}
+
+#[test]
+fn no_runtime() {
+ let (tx1, rx1) = channel::<i32>();
+ let (tx2, rx2) = channel::<i32>();
+ let t1 = thread::spawn(move || {
+ assert_eq!(rx1.recv().unwrap(), 1);
+ tx2.send(2).unwrap();
+ });
+ let t2 = thread::spawn(move || {
+ tx1.send(1).unwrap();
+ assert_eq!(rx2.recv().unwrap(), 2);
+ });
+ t1.join().ok().expect("thread panicked");
+ t2.join().ok().expect("thread panicked");
+}
+
+#[test]
+fn oneshot_single_thread_close_port_first() {
+ // Simple test of closing without sending
+ let (_tx, rx) = channel::<i32>();
+ drop(rx);
+}
+
+#[test]
+fn oneshot_single_thread_close_chan_first() {
+ // Simple test of closing without sending
+ let (tx, _rx) = channel::<i32>();
+ drop(tx);
+}
+
+#[test]
+fn oneshot_single_thread_send_port_close() {
+ // Testing that the sender cleans up the payload if receiver is closed
+ let (tx, rx) = channel::<Box<i32>>();
+ drop(rx);
+ assert!(tx.send(Box::new(0)).is_err());
+}
+
+#[test]
+fn oneshot_single_thread_recv_chan_close() {
+ // Receiving on a closed chan will panic
+ let res = thread::spawn(move || {
+ let (tx, rx) = channel::<i32>();
+ drop(tx);
+ rx.recv().unwrap();
+ })
+ .join();
+ // What is our res?
+ assert!(res.is_err());
+}
+
+#[test]
+fn oneshot_single_thread_send_then_recv() {
+ let (tx, rx) = channel::<Box<i32>>();
+ tx.send(Box::new(10)).unwrap();
+ assert!(*rx.recv().unwrap() == 10);
+}
+
+#[test]
+fn oneshot_single_thread_try_send_open() {
+ let (tx, rx) = channel::<i32>();
+ assert!(tx.send(10).is_ok());
+ assert!(rx.recv().unwrap() == 10);
+}
+
+#[test]
+fn oneshot_single_thread_try_send_closed() {
+ let (tx, rx) = channel::<i32>();
+ drop(rx);
+ assert!(tx.send(10).is_err());
+}
+
+#[test]
+fn oneshot_single_thread_try_recv_open() {
+ let (tx, rx) = channel::<i32>();
+ tx.send(10).unwrap();
+ assert!(rx.recv() == Ok(10));
+}
+
+#[test]
+fn oneshot_single_thread_try_recv_closed() {
+ let (tx, rx) = channel::<i32>();
+ drop(tx);
+ assert!(rx.recv().is_err());
+}
+
+#[test]
+fn oneshot_single_thread_peek_data() {
+ let (tx, rx) = channel::<i32>();
+ assert_eq!(rx.try_recv(), Err(TryRecvError::Empty));
+ tx.send(10).unwrap();
+ assert_eq!(rx.try_recv(), Ok(10));
+}
+
+#[test]
+fn oneshot_single_thread_peek_close() {
+ let (tx, rx) = channel::<i32>();
+ drop(tx);
+ assert_eq!(rx.try_recv(), Err(TryRecvError::Disconnected));
+ assert_eq!(rx.try_recv(), Err(TryRecvError::Disconnected));
+}
+
+#[test]
+fn oneshot_single_thread_peek_open() {
+ let (_tx, rx) = channel::<i32>();
+ assert_eq!(rx.try_recv(), Err(TryRecvError::Empty));
+}
+
+#[test]
+fn oneshot_multi_task_recv_then_send() {
+ let (tx, rx) = channel::<Box<i32>>();
+ let _t = thread::spawn(move || {
+ assert!(*rx.recv().unwrap() == 10);
+ });
+
+ tx.send(Box::new(10)).unwrap();
+}
+
+#[test]
+fn oneshot_multi_task_recv_then_close() {
+ let (tx, rx) = channel::<Box<i32>>();
+ let _t = thread::spawn(move || {
+ drop(tx);
+ });
+ let res = thread::spawn(move || {
+ assert!(*rx.recv().unwrap() == 10);
+ })
+ .join();
+ assert!(res.is_err());
+}
+
+#[test]
+fn oneshot_multi_thread_close_stress() {
+ for _ in 0..stress_factor() {
+ let (tx, rx) = channel::<i32>();
+ let _t = thread::spawn(move || {
+ drop(rx);
+ });
+ drop(tx);
+ }
+}
+
+#[test]
+fn oneshot_multi_thread_send_close_stress() {
+ for _ in 0..stress_factor() {
+ let (tx, rx) = channel::<i32>();
+ let _t = thread::spawn(move || {
+ drop(rx);
+ });
+ let _ = thread::spawn(move || {
+ tx.send(1).unwrap();
+ })
+ .join();
+ }
+}
+
+#[test]
+fn oneshot_multi_thread_recv_close_stress() {
+ for _ in 0..stress_factor() {
+ let (tx, rx) = channel::<i32>();
+ thread::spawn(move || {
+ let res = thread::spawn(move || {
+ rx.recv().unwrap();
+ })
+ .join();
+ assert!(res.is_err());
+ });
+ let _t = thread::spawn(move || {
+ thread::spawn(move || {
+ drop(tx);
+ });
+ });
+ }
+}
+
+#[test]
+fn oneshot_multi_thread_send_recv_stress() {
+ for _ in 0..stress_factor() {
+ let (tx, rx) = channel::<Box<isize>>();
+ let _t = thread::spawn(move || {
+ tx.send(Box::new(10)).unwrap();
+ });
+ assert!(*rx.recv().unwrap() == 10);
+ }
+}
+
+#[test]
+fn stream_send_recv_stress() {
+ for _ in 0..stress_factor() {
+ let (tx, rx) = channel();
+
+ send(tx, 0);
+ recv(rx, 0);
+
+ fn send(tx: Sender<Box<i32>>, i: i32) {
+ if i == 10 {
+ return;
+ }
+
+ thread::spawn(move || {
+ tx.send(Box::new(i)).unwrap();
+ send(tx, i + 1);
+ });
+ }
+
+ fn recv(rx: Receiver<Box<i32>>, i: i32) {
+ if i == 10 {
+ return;
+ }
+
+ thread::spawn(move || {
+ assert!(*rx.recv().unwrap() == i);
+ recv(rx, i + 1);
+ });
+ }
+ }
+}
+
+#[test]
+fn oneshot_single_thread_recv_timeout() {
+ let (tx, rx) = channel();
+ tx.send(()).unwrap();
+ assert_eq!(rx.recv_timeout(Duration::from_millis(1)), Ok(()));
+ assert_eq!(rx.recv_timeout(Duration::from_millis(1)), Err(RecvTimeoutError::Timeout));
+ tx.send(()).unwrap();
+ assert_eq!(rx.recv_timeout(Duration::from_millis(1)), Ok(()));
+}
+
+#[test]
+fn stress_recv_timeout_two_threads() {
+ let (tx, rx) = channel();
+ let stress = stress_factor() + 100;
+ let timeout = Duration::from_millis(100);
+
+ thread::spawn(move || {
+ for i in 0..stress {
+ if i % 2 == 0 {
+ thread::sleep(timeout * 2);
+ }
+ tx.send(1usize).unwrap();
+ }
+ });
+
+ let mut recv_count = 0;
+ loop {
+ match rx.recv_timeout(timeout) {
+ Ok(n) => {
+ assert_eq!(n, 1usize);
+ recv_count += 1;
+ }
+ Err(RecvTimeoutError::Timeout) => continue,
+ Err(RecvTimeoutError::Disconnected) => break,
+ }
+ }
+
+ assert_eq!(recv_count, stress);
+}
+
+#[test]
+fn recv_timeout_upgrade() {
+ let (tx, rx) = channel::<()>();
+ let timeout = Duration::from_millis(1);
+ let _tx_clone = tx.clone();
+
+ let start = Instant::now();
+ assert_eq!(rx.recv_timeout(timeout), Err(RecvTimeoutError::Timeout));
+ assert!(Instant::now() >= start + timeout);
+}
+
+#[test]
+fn stress_recv_timeout_shared() {
+ let (tx, rx) = channel();
+ let stress = stress_factor() + 100;
+
+ for i in 0..stress {
+ let tx = tx.clone();
+ thread::spawn(move || {
+ thread::sleep(Duration::from_millis(i as u64 * 10));
+ tx.send(1usize).unwrap();
+ });
+ }
+
+ drop(tx);
+
+ let mut recv_count = 0;
+ loop {
+ match rx.recv_timeout(Duration::from_millis(10)) {
+ Ok(n) => {
+ assert_eq!(n, 1usize);
+ recv_count += 1;
+ }
+ Err(RecvTimeoutError::Timeout) => continue,
+ Err(RecvTimeoutError::Disconnected) => break,
+ }
+ }
+
+ assert_eq!(recv_count, stress);
+}
+
+#[test]
+fn very_long_recv_timeout_wont_panic() {
+ let (tx, rx) = channel::<()>();
+ let join_handle = thread::spawn(move || rx.recv_timeout(Duration::from_secs(u64::MAX)));
+ thread::sleep(Duration::from_secs(1));
+ assert!(tx.send(()).is_ok());
+ assert_eq!(join_handle.join().unwrap(), Ok(()));
+}
+
+#[test]
+fn recv_a_lot() {
+ // Regression test that we don't run out of stack in scheduler context
+ let (tx, rx) = channel();
+ for _ in 0..10000 {
+ tx.send(()).unwrap();
+ }
+ for _ in 0..10000 {
+ rx.recv().unwrap();
+ }
+}
+
+#[test]
+fn shared_recv_timeout() {
+ let (tx, rx) = channel();
+ let total = 5;
+ for _ in 0..total {
+ let tx = tx.clone();
+ thread::spawn(move || {
+ tx.send(()).unwrap();
+ });
+ }
+
+ for _ in 0..total {
+ rx.recv().unwrap();
+ }
+
+ assert_eq!(rx.recv_timeout(Duration::from_millis(1)), Err(RecvTimeoutError::Timeout));
+ tx.send(()).unwrap();
+ assert_eq!(rx.recv_timeout(Duration::from_millis(1)), Ok(()));
+}
+
+#[test]
+fn shared_chan_stress() {
+ let (tx, rx) = channel();
+ let total = stress_factor() + 100;
+ for _ in 0..total {
+ let tx = tx.clone();
+ thread::spawn(move || {
+ tx.send(()).unwrap();
+ });
+ }
+
+ for _ in 0..total {
+ rx.recv().unwrap();
+ }
+}
+
+#[test]
+fn test_nested_recv_iter() {
+ let (tx, rx) = channel::<i32>();
+ let (total_tx, total_rx) = channel::<i32>();
+
+ let _t = thread::spawn(move || {
+ let mut acc = 0;
+ for x in rx.iter() {
+ acc += x;
+ }
+ total_tx.send(acc).unwrap();
+ });
+
+ tx.send(3).unwrap();
+ tx.send(1).unwrap();
+ tx.send(2).unwrap();
+ drop(tx);
+ assert_eq!(total_rx.recv().unwrap(), 6);
+}
+
+#[test]
+fn test_recv_iter_break() {
+ let (tx, rx) = channel::<i32>();
+ let (count_tx, count_rx) = channel();
+
+ let _t = thread::spawn(move || {
+ let mut count = 0;
+ for x in rx.iter() {
+ if count >= 3 {
+ break;
+ } else {
+ count += x;
+ }
+ }
+ count_tx.send(count).unwrap();
+ });
+
+ tx.send(2).unwrap();
+ tx.send(2).unwrap();
+ tx.send(2).unwrap();
+ let _ = tx.send(2);
+ drop(tx);
+ assert_eq!(count_rx.recv().unwrap(), 4);
+}
+
+#[test]
+fn test_recv_try_iter() {
+ let (request_tx, request_rx) = channel();
+ let (response_tx, response_rx) = channel();
+
+ // Request `x`s until we have `6`.
+ let t = thread::spawn(move || {
+ let mut count = 0;
+ loop {
+ for x in response_rx.try_iter() {
+ count += x;
+ if count == 6 {
+ return count;
+ }
+ }
+ request_tx.send(()).unwrap();
+ }
+ });
+
+ for _ in request_rx.iter() {
+ if response_tx.send(2).is_err() {
+ break;
+ }
+ }
+
+ assert_eq!(t.join().unwrap(), 6);
+}
+
+#[test]
+fn test_recv_into_iter_owned() {
+ let mut iter = {
+ let (tx, rx) = channel::<i32>();
+ tx.send(1).unwrap();
+ tx.send(2).unwrap();
+
+ rx.into_iter()
+ };
+ assert_eq!(iter.next().unwrap(), 1);
+ assert_eq!(iter.next().unwrap(), 2);
+ assert_eq!(iter.next().is_none(), true);
+}
+
+#[test]
+fn test_recv_into_iter_borrowed() {
+ let (tx, rx) = channel::<i32>();
+ tx.send(1).unwrap();
+ tx.send(2).unwrap();
+ drop(tx);
+ let mut iter = (&rx).into_iter();
+ assert_eq!(iter.next().unwrap(), 1);
+ assert_eq!(iter.next().unwrap(), 2);
+ assert_eq!(iter.next().is_none(), true);
+}
+
+#[test]
+fn try_recv_states() {
+ let (tx1, rx1) = channel::<i32>();
+ let (tx2, rx2) = channel::<()>();
+ let (tx3, rx3) = channel::<()>();
+ let _t = thread::spawn(move || {
+ rx2.recv().unwrap();
+ tx1.send(1).unwrap();
+ tx3.send(()).unwrap();
+ rx2.recv().unwrap();
+ drop(tx1);
+ tx3.send(()).unwrap();
+ });
+
+ assert_eq!(rx1.try_recv(), Err(TryRecvError::Empty));
+ tx2.send(()).unwrap();
+ rx3.recv().unwrap();
+ assert_eq!(rx1.try_recv(), Ok(1));
+ assert_eq!(rx1.try_recv(), Err(TryRecvError::Empty));
+ tx2.send(()).unwrap();
+ rx3.recv().unwrap();
+ assert_eq!(rx1.try_recv(), Err(TryRecvError::Disconnected));
+}
+
+// This bug used to end up in a livelock inside of the Receiver destructor
+// because the internal state of the Shared packet was corrupted
+#[test]
+fn destroy_upgraded_shared_port_when_sender_still_active() {
+ let (tx, rx) = channel();
+ let (tx2, rx2) = channel();
+ let _t = thread::spawn(move || {
+ rx.recv().unwrap(); // wait on a oneshot
+ drop(rx); // destroy a shared
+ tx2.send(()).unwrap();
+ });
+ // make sure the other thread has gone to sleep
+ for _ in 0..5000 {
+ thread::yield_now();
+ }
+
+ // upgrade to a shared chan and send a message
+ let t = tx.clone();
+ drop(tx);
+ t.send(()).unwrap();
+
+ // wait for the child thread to exit before we exit
+ rx2.recv().unwrap();
+}
+
+#[test]
+fn issue_32114() {
+ let (tx, _) = channel();
+ let _ = tx.send(123);
+ assert_eq!(tx.send(123), Err(SendError(123)));
+}
generated by cgit v1.2.3 (git 2.39.1) at 2024-07-07 23:06:12 +0000