Fix bug 6586:

runtime/vm/thread_test.cc

Index: runtime/vm/thread_test.cc
===================================================================
--- runtime/vm/thread_test.cc	(revision 14653)
+++ runtime/vm/thread_test.cc	(working copy)
@@ -39,18 +39,33 @@
   monitor->Enter();
   monitor->Exit();
 
-  {
+  const int kNumAttempts = 5;
+  int attempts = 0;
+  while (attempts < kNumAttempts) {
     MonitorLocker ml(monitor);
     int64_t start = OS::GetCurrentTimeMillis();
     int64_t wait_time = 2017;
     Monitor::WaitResult wait_result = ml.Wait(wait_time);
     int64_t stop = OS::GetCurrentTimeMillis();
+
+    // We expect to be timing out here.
     EXPECT_EQ(Monitor::kTimedOut, wait_result);
+
+    // Check whether this attempt falls within the exptected time limits.
+    int64_t wakeup_time = stop - start;
+    OS::Print("wakeup_time: %"Pd64"\n", wakeup_time);
     const int kAcceptableTimeJitter = 20;  // Measured in milliseconds.
-    EXPECT_LE(wait_time - kAcceptableTimeJitter, stop - start);
     const int kAcceptableWakeupDelay = 150;  // Measured in milliseconds.
-    EXPECT_GE(wait_time + kAcceptableWakeupDelay, stop - start);
+    if (((wait_time - kAcceptableTimeJitter) <= wakeup_time) &&
+        (wakeup_time <= (wait_time + kAcceptableWakeupDelay))) {
+      break;
+    }
+
+    // Record the attempt.
+    attempts++;
   }
+  EXPECT_LT(attempts, kNumAttempts);
+
   // The isolate shutdown and the destruction of the mutex are out-of-order on
   // purpose.
   isolate->Shutdown();