---

yaml
---
r: 64863
b: refs/heads/snap-stage3
c: 3f6b4c2
h: refs/heads/master
i:
  64861: a57a799
  64859: ef5ac4b
  64855: eabe26a
  64847: a961d8c
  64831: 6f2e4d6
v: v3

Author: bblum

[refs]

@@ -1,7 +1,7 @@
 ---
 refs/heads/master: 2d28d645422c1617be58c8ca7ad9a457264ca850
 refs/heads/snap-stage1: e33de59e47c5076a89eadeb38f4934f58a3618a6
-refs/heads/snap-stage3: cccfa8acc450631fe9520abbe40360927ce1961d
+refs/heads/snap-stage3: 3f6b4c24ec2234a06632234eaf3014ae0e4adc66
 refs/heads/try: 7b78b52e602bb3ea8174f9b2006bff3315f03ef9
 refs/tags/release-0.1: 1f5c5126e96c79d22cb7862f75304136e204f105
 refs/heads/ndm: f3868061cd7988080c30d6d5bf352a5a5fe2460b

branches/snap-stage3/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