sync: name mpsc semaphore types (#5146)

Make code easier to read. No functional/perf changes.

tokio/src/sync/mpsc/bounded.rs

@@ -143,7 +143,10 @@ pub struct Receiver<T> {
 #[track_caller]
 pub fn channel<T>(buffer: usize) -> (Sender<T>, Receiver<T>) {
     assert!(buffer > 0, "mpsc bounded channel requires buffer > 0");
-    let semaphore = (semaphore::Semaphore::new(buffer), buffer);
+    let semaphore = Semaphore {
+        semaphore: semaphore::Semaphore::new(buffer),
+        bound: buffer,
+    };
     let (tx, rx) = chan::channel(semaphore);
 
     let tx = Sender::new(tx);
@@ -154,7 +157,11 @@ pub fn channel<T>(buffer: usize) -> (Sender<T>, Receiver<T>) {
 
 /// Channel semaphore is a tuple of the semaphore implementation and a `usize`
 /// representing the channel bound.
-type Semaphore = (semaphore::Semaphore, usize);
+#[derive(Debug)]
+pub(crate) struct Semaphore {
+    pub(crate) semaphore: semaphore::Semaphore,
+    pub(crate) bound: usize,
+}
 
 impl<T> Receiver<T> {
     pub(crate) fn new(chan: chan::Rx<T, Semaphore>) -> Receiver<T> {
@@ -572,7 +579,7 @@ impl<T> Sender<T> {
     /// }
     /// ```
     pub fn try_send(&self, message: T) -> Result<(), TrySendError<T>> {
-        match self.chan.semaphore().0.try_acquire(1) {
+        match self.chan.semaphore().semaphore.try_acquire(1) {
             Ok(_) => {}
             Err(TryAcquireError::Closed) => return Err(TrySendError::Closed(message)),
             Err(TryAcquireError::NoPermits) => return Err(TrySendError::Full(message)),
@@ -852,7 +859,7 @@ impl<T> Sender<T> {
     }
 
     async fn reserve_inner(&self) -> Result<(), SendError<()>> {
-        match self.chan.semaphore().0.acquire(1).await {
+        match self.chan.semaphore().semaphore.acquire(1).await {
             Ok(_) => Ok(()),
             Err(_) => Err(SendError(())),
         }
@@ -902,7 +909,7 @@ impl<T> Sender<T> {
     /// }
     /// ```
     pub fn try_reserve(&self) -> Result<Permit<'_, T>, TrySendError<()>> {
-        match self.chan.semaphore().0.try_acquire(1) {
+        match self.chan.semaphore().semaphore.try_acquire(1) {
             Ok(_) => {}
             Err(TryAcquireError::Closed) => return Err(TrySendError::Closed(())),
             Err(TryAcquireError::NoPermits) => return Err(TrySendError::Full(())),
@@ -967,7 +974,7 @@ impl<T> Sender<T> {
     /// }
     /// ```
     pub fn try_reserve_owned(self) -> Result<OwnedPermit<T>, TrySendError<Self>> {
-        match self.chan.semaphore().0.try_acquire(1) {
+        match self.chan.semaphore().semaphore.try_acquire(1) {
             Ok(_) => {}
             Err(TryAcquireError::Closed) => return Err(TrySendError::Closed(self)),
             Err(TryAcquireError::NoPermits) => return Err(TrySendError::Full(self)),
@@ -1028,7 +1035,7 @@ impl<T> Sender<T> {
     /// [`channel`]: channel
     /// [`max_capacity`]: Sender::max_capacity
     pub fn capacity(&self) -> usize {
-        self.chan.semaphore().0.available_permits()
+        self.chan.semaphore().semaphore.available_permits()
     }
 
     /// Converts the `Sender` to a [`WeakSender`] that does not count
@@ -1074,7 +1081,7 @@ impl<T> Sender<T> {
     /// [`max_capacity`]: Sender::max_capacity
     /// [`capacity`]: Sender::capacity
     pub fn max_capacity(&self) -> usize {
-        self.chan.semaphore().1
+        self.chan.semaphore().bound
     }
 }
 

tokio/src/sync/mpsc/chan.rs

@@ -4,7 +4,7 @@ use crate::loom::sync::atomic::AtomicUsize;
 use crate::loom::sync::Arc;
 use crate::park::thread::CachedParkThread;
 use crate::sync::mpsc::error::TryRecvError;
-use crate::sync::mpsc::list;
+use crate::sync::mpsc::{bounded, list, unbounded};
 use crate::sync::notify::Notify;
 
 use std::fmt;
@@ -12,7 +12,6 @@ use std::process;
 use std::sync::atomic::Ordering::{AcqRel, Acquire, Relaxed, Release};
 use std::task::Poll::{Pending, Ready};
 use std::task::{Context, Poll};
-use std::usize;
 
 /// Channel sender.
 pub(crate) struct Tx<T, S> {
@@ -382,29 +381,29 @@ impl<T, S> Drop for Chan<T, S> {
 
 // ===== impl Semaphore for (::Semaphore, capacity) =====
 
-impl Semaphore for (crate::sync::batch_semaphore::Semaphore, usize) {
+impl Semaphore for bounded::Semaphore {
     fn add_permit(&self) {
-        self.0.release(1)
+        self.semaphore.release(1)
     }
 
     fn is_idle(&self) -> bool {
-        self.0.available_permits() == self.1
+        self.semaphore.available_permits() == self.bound
     }
 
     fn close(&self) {
-        self.0.close();
+        self.semaphore.close();
     }
 
     fn is_closed(&self) -> bool {
-        self.0.is_closed()
+        self.semaphore.is_closed()
     }
 }
 
 // ===== impl Semaphore for AtomicUsize =====
 
-impl Semaphore for AtomicUsize {
+impl Semaphore for unbounded::Semaphore {
     fn add_permit(&self) {
-        let prev = self.fetch_sub(2, Release);
+        let prev = self.0.fetch_sub(2, Release);
 
         if prev >> 1 == 0 {
             // Something went wrong
@@ -413,14 +412,14 @@ impl Semaphore for AtomicUsize {
     }
 
     fn is_idle(&self) -> bool {
-        self.load(Acquire) >> 1 == 0
+        self.0.load(Acquire) >> 1 == 0
     }
 
     fn close(&self) {
-        self.fetch_or(1, Release);
+        self.0.fetch_or(1, Release);
     }
 
     fn is_closed(&self) -> bool {
-        self.load(Acquire) & 1 == 1
+        self.0.load(Acquire) & 1 == 1
     }
 }

tokio/src/sync/mpsc/unbounded.rs

@@ -61,7 +61,7 @@ impl<T> fmt::Debug for UnboundedReceiver<T> {
 /// the channel. Using an `unbounded` channel has the ability of causing the
 /// process to run out of memory. In this case, the process will be aborted.
 pub fn unbounded_channel<T>() -> (UnboundedSender<T>, UnboundedReceiver<T>) {
-    let (tx, rx) = chan::channel(AtomicUsize::new(0));
+    let (tx, rx) = chan::channel(Semaphore(AtomicUsize::new(0)));
 
     let tx = UnboundedSender::new(tx);
     let rx = UnboundedReceiver::new(rx);
@@ -70,7 +70,8 @@ pub fn unbounded_channel<T>() -> (UnboundedSender<T>, UnboundedReceiver<T>) {
 }
 
 /// No capacity
-type Semaphore = AtomicUsize;
+#[derive(Debug)]
+pub(crate) struct Semaphore(pub(crate) AtomicUsize);
 
 impl<T> UnboundedReceiver<T> {
     pub(crate) fn new(chan: chan::Rx<T, Semaphore>) -> UnboundedReceiver<T> {
@@ -279,7 +280,7 @@ impl<T> UnboundedSender<T> {
         use std::process;
         use std::sync::atomic::Ordering::{AcqRel, Acquire};
 
-        let mut curr = self.chan.semaphore().load(Acquire);
+        let mut curr = self.chan.semaphore().0.load(Acquire);
 
         loop {
             if curr & 1 == 1 {
@@ -295,6 +296,7 @@ impl<T> UnboundedSender<T> {
             match self
                 .chan
                 .semaphore()
+                .0
                 .compare_exchange(curr, curr + 2, AcqRel, Acquire)
             {
                 Ok(_) => return true,