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Diffstat (limited to 'library/std/src/sync/mpsc/stream.rs')
| -rw-r--r-- | library/std/src/sync/mpsc/stream.rs | 457 |
1 files changed, 0 insertions, 457 deletions
diff --git a/library/std/src/sync/mpsc/stream.rs b/library/std/src/sync/mpsc/stream.rs deleted file mode 100644 index 4592e9141..000000000 --- a/library/std/src/sync/mpsc/stream.rs +++ /dev/null @@ -1,457 +0,0 @@ -/// 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 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); - } -} |