---

yaml
---
r: 69490
b: refs/heads/auto
c: 3f6b4c2
h: refs/heads/master
v: v3

Author: bblum

[refs]

@@ -14,6 +14,6 @@ refs/heads/try3: 9387340aab40a73e8424c48fd42f0c521a4875c0
 refs/tags/release-0.3.1: 495bae036dfe5ec6ceafd3312b4dca48741e845b
 refs/tags/release-0.4: e828ea2080499553b97dfe33b3f4d472b4562ad7
 refs/tags/release-0.5: 7e3bcfbf21278251ee936ad53e92e9b719702d73
-refs/heads/auto: cccfa8acc450631fe9520abbe40360927ce1961d
+refs/heads/auto: 3f6b4c24ec2234a06632234eaf3014ae0e4adc66
 refs/heads/servo: af82457af293e2a842ba6b7759b70288da276167
 refs/tags/release-0.6: b4ebcfa1812664df5e142f0134a5faea3918544c

branches/auto/src/libstd/rt/comm.rs

@@ -180,11 +180,25 @@ impl<T> PortOne<T> {
 }
 
 impl<T> Select for PortOne<T> {
-    #[inline]
+    #[inline] #[cfg(not(test))]
     fn optimistic_check(&mut self) -> bool {
         unsafe { (*self.packet()).state.load(Acquire) == STATE_ONE }
     }
 
+    #[inline] #[cfg(test)]
+    fn optimistic_check(&mut self) -> bool {
+        // The optimistic check is never necessary for correctness. For testing
+        // purposes, making it randomly return false simulates a racing sender.
+        use rand::{Rand, rng};
+        let mut rng = rng();
+        let actually_check = Rand::rand(&mut rng);
+        if actually_check {
+            unsafe { (*self.packet()).state.load(Acquire) == STATE_ONE }
+        } else {
+            false
+        }
+    }
+
     fn block_on(&mut self, sched: &mut Scheduler, task: BlockedTask) -> bool {
         unsafe {
             // Atomically swap the task pointer into the Packet state, issuing