Merging upstream version 1.72.1+dfsg1.

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

4 files changed, 37 insertions, 29 deletions

diff --git a/library/std/src/sync/barrier.rs b/library/std/src/sync/barrier.rs
index 11836b7b6..e39254aa4 100644
--- a/library/std/src/sync/barrier.rs
+++ b/library/std/src/sync/barrier.rs
@@ -13,9 +13,10 @@ use crate::sync::{Condvar, Mutex};
 /// use std::sync::{Arc, Barrier};
 /// use std::thread;
 ///
-/// let mut handles = Vec::with_capacity(10);
-/// let barrier = Arc::new(Barrier::new(10));
-/// for _ in 0..10 {
+/// let n = 10;
+/// let mut handles = Vec::with_capacity(n);
+/// let barrier = Arc::new(Barrier::new(n));
+/// for _ in 0..n {
 ///     let c = Arc::clone(&barrier);
 ///     // The same messages will be printed together.
 ///     // You will NOT see any interleaving.
@@ -105,9 +106,10 @@ impl Barrier {
     /// use std::sync::{Arc, Barrier};
     /// use std::thread;
     ///
-    /// let mut handles = Vec::with_capacity(10);
-    /// let barrier = Arc::new(Barrier::new(10));
-    /// for _ in 0..10 {
+    /// let n = 10;
+    /// let mut handles = Vec::with_capacity(n);
+    /// let barrier = Arc::new(Barrier::new(n));
+    /// for _ in 0..n {
     ///     let c = Arc::clone(&barrier);
     ///     // The same messages will be printed together.
     ///     // You will NOT see any interleaving.
diff --git a/library/std/src/sync/mpmc/waker.rs b/library/std/src/sync/mpmc/waker.rs
index 4912ca4f8..9aab1b941 100644
--- a/library/std/src/sync/mpmc/waker.rs
+++ b/library/std/src/sync/mpmc/waker.rs
@@ -66,26 +66,32 @@ impl Waker {
     /// Attempts to find another thread's entry, select the operation, and wake it up.
     #[inline]
     pub(crate) fn try_select(&mut self) -> Option<Entry> {
-        self.selectors
-            .iter()
-            .position(|selector| {
-                // Does the entry belong to a different thread?
-                selector.cx.thread_id() != current_thread_id()
-                    && selector // Try selecting this operation.
-                        .cx
-                        .try_select(Selected::Operation(selector.oper))
-                        .is_ok()
-                    && {
-                        // Provide the packet.
-                        selector.cx.store_packet(selector.packet);
-                        // Wake the thread up.
-                        selector.cx.unpark();
-                        true
-                    }
-            })
-            // Remove the entry from the queue to keep it clean and improve
-            // performance.
-            .map(|pos| self.selectors.remove(pos))
+        if self.selectors.is_empty() {
+            None
+        } else {
+            let thread_id = current_thread_id();
+
+            self.selectors
+                .iter()
+                .position(|selector| {
+                    // Does the entry belong to a different thread?
+                    selector.cx.thread_id() != thread_id
+                        && selector // Try selecting this operation.
+                            .cx
+                            .try_select(Selected::Operation(selector.oper))
+                            .is_ok()
+                        && {
+                            // Provide the packet.
+                            selector.cx.store_packet(selector.packet);
+                            // Wake the thread up.
+                            selector.cx.unpark();
+                            true
+                        }
+                })
+                // Remove the entry from the queue to keep it clean and improve
+                // performance.
+                .map(|pos| self.selectors.remove(pos))
+        }
     }
 
     /// Notifies all operations waiting to be ready.
diff --git a/library/std/src/sync/mpsc/mod.rs b/library/std/src/sync/mpsc/mod.rs
index 0e0c87d1c..c00134c8b 100644
--- a/library/std/src/sync/mpsc/mod.rs
+++ b/library/std/src/sync/mpsc/mod.rs
@@ -347,8 +347,8 @@ pub struct Sender<T> {
 #[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> {}
+#[stable(feature = "mpsc_sender_sync", since = "1.72.0")]
+unsafe impl<T: Send> Sync for Sender<T> {}
 
 /// The sending-half of Rust's synchronous [`sync_channel`] type.
 ///
diff --git a/library/std/src/sync/once.rs b/library/std/src/sync/once.rs
index 1b17c3108..8c46080e4 100644
--- a/library/std/src/sync/once.rs
+++ b/library/std/src/sync/once.rs
@@ -91,7 +91,7 @@ impl Once {
     /// return).
     ///
     /// If the given closure recursively invokes `call_once` on the same [`Once`]
-    /// instance the exact behavior is not specified, allowed outcomes are
+    /// instance, the exact behavior is not specified: allowed outcomes are
     /// a panic or a deadlock.
     ///
     /// # Examples