Bug 1139856 - do not lose wakeups. r=luke

js/src/builtin/AtomicsObject.cpp

@@ -1032,7 +1032,13 @@ js::FutexRuntime::destroyInstance()
 bool
 js::FutexRuntime::isWaiting()
 {
-    return state_ == Waiting || state_ == WaitingInterrupted;
+    // When a worker is awoken for an interrupt it goes into state
+    // WaitingNotifiedForInterrupt for a short time before it actually
+    // wakes up and goes into WaitingInterrupted.  In those states the
+    // worker is still waiting, and if an explicit wake arrives the
+    // worker transitions to Woken.  See further comments in
+    // FutexRuntime::wait().
+    return state_ == Waiting || state_ == WaitingInterrupted || state_ == WaitingNotifiedForInterrupt;
 }
 
 bool
@@ -1102,7 +1108,7 @@ js::FutexRuntime::wait(JSContext* cx, double timeout_ms, AtomicsObject::FutexWai
             *result = AtomicsObject::FutexOK;
             goto finished;
 
-          case FutexRuntime::WokenForJSInterrupt:
+          case FutexRuntime::WaitingNotifiedForInterrupt:
             // The interrupt handler may reenter the engine.  In that case
             // there are two complications:
             //
@@ -1112,7 +1118,7 @@ js::FutexRuntime::wait(JSContext* cx, double timeout_ms, AtomicsObject::FutexWai
             //   To that end, we flag the thread as interrupted around
             //   the interrupt and check state_ when the interrupt
             //   handler returns.  A futexWake() call that reaches the
-            //   runtime during the interrupt sets state_ to woken.
+            //   runtime during the interrupt sets state_ to Woken.
             //
             // - It is in principle possible for futexWait() to be
             //   reentered on the same thread/runtime and waiting on the
@@ -1160,7 +1166,7 @@ js::FutexRuntime::wake(WakeReason reason)
     MOZ_ASSERT(lockHolder_ == PR_GetCurrentThread());
     MOZ_ASSERT(isWaiting());
 
-    if (state_ == WaitingInterrupted && reason == WakeExplicit) {
+    if ((state_ == WaitingInterrupted || state_ == WaitingNotifiedForInterrupt) && reason == WakeExplicit) {
         state_ = Woken;
         return;
     }
@@ -1169,7 +1175,9 @@ js::FutexRuntime::wake(WakeReason reason)
         state_ = Woken;
         break;
       case WakeForJSInterrupt:
-        state_ = WokenForJSInterrupt;
+        if (state_ == WaitingNotifiedForInterrupt)
+            return;
+        state_ = WaitingNotifiedForInterrupt;
         break;
       default:
         MOZ_CRASH();

js/src/builtin/AtomicsObject.h

@@ -97,19 +97,22 @@ public:
     //
     // If the thread is waiting in a call to futexWait() and the
     // reason is WakeForJSInterrupt then the futexWait() will return
-    // with WokenForJSInterrupt; in the latter case the caller of
-    // futexWait() must handle the interrupt.
+    // with WaitingNotifiedForInterrupt; in the latter case the caller
+    // of futexWait() must handle the interrupt.
     void wake(WakeReason reason);
 
     bool isWaiting();
 
   private:
     enum FutexState {
-        Idle,                   // We are not waiting or woken
-        Waiting,                // We are waiting, nothing has happened yet
-        WaitingInterrupted,     // We are waiting, but have been interrupted
-        Woken,                  // Woken by a script call to futexWake
-        WokenForJSInterrupt     // Woken by an interrupt handler
+        Idle,                        // We are not waiting or woken
+        Waiting,                     // We are waiting, nothing has happened yet
+        WaitingNotifiedForInterrupt, // We are waiting, but have been interrupted,
+                                     //   and have not yet started running the
+                                     //   interrupt handler
+        WaitingInterrupted,          // We are waiting, but have been interrupted
+                                     //   and are running the interrupt handler
+        Woken                        // Woken by a script call to futexWake
     };
 
     // Condition variable that this runtime will wait on.