Bug 1829983 - Disabled assert that's invalid on Windows r=dthayer

Differential Revision: https://phabricator.services.mozilla.com/D180882

mozglue/misc/TimeStamp.h

@@ -369,6 +369,20 @@ typedef BaseTimeDuration<TimeDurationValueCalculator> TimeDuration;
  * Note that, since TimeStamp objects are small, prefer to pass them by value
  * unless there is a specific reason not to do so.
  */
+#if defined(XP_WIN)
+// If this static_assert fails then possibly the warning comment below is no
+// longer valid and should be removed.
+static_assert(sizeof(TimeStampValue) > 8);
+#endif
+/*
+ * WARNING: On Windows, each TimeStamp is represented internally by two
+ * different raw values (one from GTC and one from QPC) and which value gets
+ * used for a given operation depends on whether both operands have QPC values
+ * or not. This duality of values can lead to some surprising results when
+ * mixing TimeStamps with and without QPC values, such as comparisons being
+ * non-transitive (ie, a > b > c might not imply a > c). See bug 1829983 for
+ * more details/an example.
+ */
 class TimeStamp {
  public:
   /**

xpcom/threads/TimerThread.cpp

@@ -26,13 +26,6 @@
 
 using namespace mozilla;
 
-// Bug 1829983 reports an assertion failure that (so far) has only failed once
-// in over a month of the assert existing. This #define enables some additional
-// output that should get printed out if the assert fails again.
-#if defined(XP_WIN) && defined(DEBUG)
-#  define HACK_OUTPUT_FOR_BUG_1829983
-#endif
-
 // Uncomment the following line to enable runtime stats during development.
 // #define TIMERS_RUNTIME_STATS
 
@@ -684,31 +677,13 @@ TimeStamp TimerThread::ComputeWakeupTimeFromTimers() const {
     MOZ_ASSERT(bundleWakeup <= cutoffTime);
   }
 
-#ifdef HACK_OUTPUT_FOR_BUG_1829983
-  const bool assertCondition =
-      bundleWakeup - mTimers[0].Timeout() <=
-      ComputeAcceptableFiringDelay(mTimers[0].Delay(), minTimerDelay,
-                                   maxTimerDelay);
-  if (!assertCondition) {
-    printf_stderr("*** Special TimerThread debug output ***\n");
-    const int64_t tDMin = minTimerDelay.GetValue();
-    const int64_t tDMax = maxTimerDelay.GetValue();
-    printf_stderr("%16llx / %16llx\n", tDMin, tDMax);
-    const size_t l = mTimers.Length();
-    for (size_t i = 0; i < l; ++i) {
-      const Entry& e = mTimers[i];
-      const TimeStamp tS = e.Timeout();
-      const TimeStampValue tSV = tS.GetValue();
-      const TimeDuration d = e.Delay();
-      printf_stderr("[%5zu] %16llx / %16llx / %d / %d / %16llx\n", i, tSV.GTC(),
-                    tSV.QPC(), (int)tSV.IsNull(), (int)tSV.HasQPC(),
-                    d.GetValue());
-    }
-  }
-#endif
+#if !defined(XP_WIN)
+  // Due to the fact that, on Windows, each TimeStamp object holds two distinct
+  // "values", this assert is not valid there. See bug 1829983 for the details.
   MOZ_ASSERT(bundleWakeup - mTimers[0].Timeout() <=
              ComputeAcceptableFiringDelay(mTimers[0].Delay(), minTimerDelay,
                                           maxTimerDelay));
+#endif
 
   return bundleWakeup;
 }