Auto merge of #35048 - tmiasko:monotonic-wait-timeout, r=alexcrichton

Use monotonic time in condition variables.

Configure condition variables to use monotonic time using
pthread_condattr_setclock on systems where this is possible.
This fixes the issue when thread waiting on condition variable is
woken up too late when system time is moved backwards.

1 files changed, 13 insertions, 1 deletions

diff --git a/src/libstd/sync/condvar.rs b/src/libstd/sync/condvar.rs
index 1f480f6d4a9..4c946e613ea 100644
--- a/src/libstd/sync/condvar.rs
+++ b/src/libstd/sync/condvar.rs
@@ -80,10 +80,14 @@ impl Condvar {
     /// notified.
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn new() -> Condvar {
-        Condvar {
+        let mut c = Condvar {
             inner: box sys::Condvar::new(),
             mutex: AtomicUsize::new(0),
+        };
+        unsafe {
+            c.inner.init();
         }
+        c
     }
 
     /// Blocks the current thread until this condition variable receives a
@@ -138,6 +142,10 @@ impl Condvar {
     /// differences that may not cause the maximum amount of time
     /// waited to be precisely `ms`.
     ///
+    /// Note that the best effort is made to ensure that the time waited is
+    /// measured with a monotonic clock, and not affected by the changes made to
+    /// the system time.
+    ///
     /// The returned boolean is `false` only if the timeout is known
     /// to have elapsed.
     ///
@@ -162,6 +170,10 @@ impl Condvar {
     /// preemption or platform differences that may not cause the maximum
     /// amount of time waited to be precisely `dur`.
     ///
+    /// Note that the best effort is made to ensure that the time waited is
+    /// measured with a monotonic clock, and not affected by the changes made to
+    /// the system time.
+    ///
     /// The returned `WaitTimeoutResult` value indicates if the timeout is
     /// known to have elapsed.
     ///