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-rw-r--r--third_party/rust/crossbeam-channel/src/counter.rs144
1 files changed, 144 insertions, 0 deletions
diff --git a/third_party/rust/crossbeam-channel/src/counter.rs b/third_party/rust/crossbeam-channel/src/counter.rs
new file mode 100644
index 0000000000..2c27f7c6b2
--- /dev/null
+++ b/third_party/rust/crossbeam-channel/src/counter.rs
@@ -0,0 +1,144 @@
+//! Reference counter for channels.
+
+use std::isize;
+use std::ops;
+use std::process;
+use std::sync::atomic::{AtomicBool, AtomicUsize, Ordering};
+
+/// Reference counter internals.
+struct Counter<C> {
+ /// The number of senders associated with the channel.
+ senders: AtomicUsize,
+
+ /// The number of receivers associated with the channel.
+ receivers: AtomicUsize,
+
+ /// Set to `true` if the last sender or the last receiver reference deallocates the channel.
+ destroy: AtomicBool,
+
+ /// The internal channel.
+ chan: C,
+}
+
+/// Wraps a channel into the reference counter.
+pub(crate) fn new<C>(chan: C) -> (Sender<C>, Receiver<C>) {
+ let counter = Box::into_raw(Box::new(Counter {
+ senders: AtomicUsize::new(1),
+ receivers: AtomicUsize::new(1),
+ destroy: AtomicBool::new(false),
+ chan,
+ }));
+ let s = Sender { counter };
+ let r = Receiver { counter };
+ (s, r)
+}
+
+/// The sending side.
+pub(crate) struct Sender<C> {
+ counter: *mut Counter<C>,
+}
+
+impl<C> Sender<C> {
+ /// Returns the internal `Counter`.
+ fn counter(&self) -> &Counter<C> {
+ unsafe { &*self.counter }
+ }
+
+ /// Acquires another sender reference.
+ pub(crate) fn acquire(&self) -> Sender<C> {
+ let count = self.counter().senders.fetch_add(1, Ordering::Relaxed);
+
+ // Cloning senders and calling `mem::forget` on the clones could potentially overflow the
+ // counter. It's very difficult to recover sensibly from such degenerate scenarios so we
+ // just abort when the count becomes very large.
+ if count > isize::MAX as usize {
+ process::abort();
+ }
+
+ Sender {
+ counter: self.counter,
+ }
+ }
+
+ /// Releases the sender reference.
+ ///
+ /// Function `disconnect` will be called if this is the last sender reference.
+ pub(crate) unsafe fn release<F: FnOnce(&C) -> bool>(&self, disconnect: F) {
+ if self.counter().senders.fetch_sub(1, Ordering::AcqRel) == 1 {
+ disconnect(&self.counter().chan);
+
+ if self.counter().destroy.swap(true, Ordering::AcqRel) {
+ drop(Box::from_raw(self.counter));
+ }
+ }
+ }
+}
+
+impl<C> ops::Deref for Sender<C> {
+ type Target = C;
+
+ fn deref(&self) -> &C {
+ &self.counter().chan
+ }
+}
+
+impl<C> PartialEq for Sender<C> {
+ fn eq(&self, other: &Sender<C>) -> bool {
+ self.counter == other.counter
+ }
+}
+
+/// The receiving side.
+pub(crate) struct Receiver<C> {
+ counter: *mut Counter<C>,
+}
+
+impl<C> Receiver<C> {
+ /// Returns the internal `Counter`.
+ fn counter(&self) -> &Counter<C> {
+ unsafe { &*self.counter }
+ }
+
+ /// Acquires another receiver reference.
+ pub(crate) fn acquire(&self) -> Receiver<C> {
+ let count = self.counter().receivers.fetch_add(1, Ordering::Relaxed);
+
+ // Cloning receivers and calling `mem::forget` on the clones could potentially overflow the
+ // counter. It's very difficult to recover sensibly from such degenerate scenarios so we
+ // just abort when the count becomes very large.
+ if count > isize::MAX as usize {
+ process::abort();
+ }
+
+ Receiver {
+ counter: self.counter,
+ }
+ }
+
+ /// Releases the receiver reference.
+ ///
+ /// Function `disconnect` will be called if this is the last receiver reference.
+ pub(crate) unsafe fn release<F: FnOnce(&C) -> bool>(&self, disconnect: F) {
+ if self.counter().receivers.fetch_sub(1, Ordering::AcqRel) == 1 {
+ disconnect(&self.counter().chan);
+
+ if self.counter().destroy.swap(true, Ordering::AcqRel) {
+ drop(Box::from_raw(self.counter));
+ }
+ }
+ }
+}
+
+impl<C> ops::Deref for Receiver<C> {
+ type Target = C;
+
+ fn deref(&self) -> &C {
+ &self.counter().chan
+ }
+}
+
+impl<C> PartialEq for Receiver<C> {
+ fn eq(&self, other: &Receiver<C>) -> bool {
+ self.counter == other.counter
+ }
+}