sync: add wait_timeout method to condvar wrapper

Adds a method wait_timeout to sync::Condvar which wraps
std::sync::Condvar's wait_timeout.

BUG=None
TEST=cargo test

Change-Id: I9888568b8bac779006080b505762016b6ca381e6
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosvm/+/1789913
Tested-by: Fletcher Woodruff <fletcherw@chromium.org>
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Dylan Reid <dgreid@chromium.org>
Reviewed-by: Chih-Yang Hsia <paulhsia@chromium.org>
Commit-Queue: Fletcher Woodruff <fletcherw@chromium.org>

sync/src/condvar.rs

@@ -3,7 +3,8 @@
 // found in the LICENSE file.
 
 use std::fmt::{self, Debug};
-use std::sync::{Condvar as StdCondvar, MutexGuard};
+use std::sync::{Condvar as StdCondvar, MutexGuard, WaitTimeoutResult};
+use std::time::Duration;
 
 /// A Condition Variable.
 #[derive(Default)]
@@ -27,6 +28,19 @@ impl Condvar {
         }
     }
 
+    /// Waits on a condvar, blocking the current thread until it is notified
+    /// or the specified duration has elapsed.
+    pub fn wait_timeout<'a, T>(
+        &self,
+        guard: MutexGuard<'a, T>,
+        dur: Duration,
+    ) -> (MutexGuard<'a, T>, WaitTimeoutResult) {
+        match self.std.wait_timeout(guard, dur) {
+            Ok(result) => result,
+            Err(_) => panic!("condvar is poisoned"),
+        }
+    }
+
     /// Notifies one thread blocked by this condvar.
     pub fn notify_one(&self) {
         self.std.notify_one();