Bug 1522316, use medium high priority queue for worker->main thread control messages, r=baku

If main thread is busy handling runnables in the normal priority queue, control-type of messages from
workers are possibly postponed to run after those. That can lead to bad performance, if the page
expects workers to be able to proceed simultanously with the main thread.
This patch makes the control messages to use medium high priority queue in order to try to
ensure they are handled in timely manner.
Pref dom.worker.use_medium_high_event_queue can be set to false to disable this new behavior.

Differential Revision: https://phabricator.services.mozilla.com/D22128

--HG--
extra : rebase_source : 447dec6dbcccaa0206a1815c21ccf713c523fc91

dom/console/Console.cpp

@@ -712,6 +712,8 @@ class ConsoleWorkerRunnable : public WorkerProxyToMainThreadRunnable,
   // This method is called in the owning thread of the Console object.
   virtual void ReleaseData() = 0;
 
+  bool ForMessaging() const override { return true; }
+
   // This must be released on the worker thread.
   RefPtr<Console> mConsole;
 

dom/serviceworkers/ServiceWorkerPrivate.cpp

@@ -639,7 +639,9 @@ class LifeCycleEventWatcher final : public ExtendableEventCallback {
                                 [self]() { self->ReportResult(false); });
     if (NS_WARN_IF(!mWorkerRef)) {
       mCallback->SetResult(false);
-      nsresult rv = workerPrivate->DispatchToMainThread(mCallback);
+      // Using DispatchToMainThreadForMessaging so that state update on
+      // the main thread doesn't happen too soon.
+      nsresult rv = workerPrivate->DispatchToMainThreadForMessaging(mCallback);
       Unused << NS_WARN_IF(NS_FAILED(rv));
       return false;
     }
@@ -655,7 +657,9 @@ class LifeCycleEventWatcher final : public ExtendableEventCallback {
     }
 
     mCallback->SetResult(aResult);
-    nsresult rv = mWorkerRef->Private()->DispatchToMainThread(mCallback);
+    // Using DispatchToMainThreadForMessaging so that state update on
+    // the main thread doesn't happen too soon.
+    nsresult rv = mWorkerRef->Private()->DispatchToMainThreadForMessaging(mCallback);
     if (NS_WARN_IF(NS_FAILED(rv))) {
       MOZ_CRASH("Failed to dispatch life cycle event handler.");
     }

dom/workers/WorkerDebugger.cpp

@@ -400,7 +400,8 @@ void WorkerDebugger::PostMessageToDebugger(const nsAString& aMessage) {
 
   RefPtr<PostDebuggerMessageRunnable> runnable =
       new PostDebuggerMessageRunnable(this, aMessage);
-  if (NS_FAILED(mWorkerPrivate->DispatchToMainThread(runnable.forget()))) {
+  if (NS_FAILED(mWorkerPrivate->DispatchToMainThreadForMessaging(
+          runnable.forget()))) {
     NS_WARNING("Failed to post message to debugger on main thread!");
   }
 }
@@ -422,7 +423,8 @@ void WorkerDebugger::ReportErrorToDebugger(const nsAString& aFilename,
 
   RefPtr<ReportDebuggerErrorRunnable> runnable =
       new ReportDebuggerErrorRunnable(this, aFilename, aLineno, aMessage);
-  if (NS_FAILED(mWorkerPrivate->DispatchToMainThread(runnable.forget()))) {
+  if (NS_FAILED(mWorkerPrivate->DispatchToMainThreadForMessaging(
+          runnable.forget()))) {
     NS_WARNING("Failed to report error to debugger on main thread!");
   }
 }

dom/workers/WorkerPrivate.cpp

@@ -1032,8 +1032,8 @@ class WorkerPrivate::MemoryReporter final : public nsIMemoryReporter {
 
       WorkerPrivate* workerPrivate = GetCurrentThreadWorkerPrivate();
       MOZ_ASSERT(workerPrivate);
-      MOZ_ALWAYS_SUCCEEDS(
-          workerPrivate->DispatchToMainThread(mFinishCollectRunnable.forget()));
+      MOZ_ALWAYS_SUCCEEDS(workerPrivate->DispatchToMainThreadForMessaging(
+          mFinishCollectRunnable.forget()));
     }
   };
 
@@ -1337,9 +1337,9 @@ nsresult WorkerPrivate::Dispatch(already_AddRefed<WorkerRunnable> aRunnable,
   return DispatchLockHeld(std::move(aRunnable), aSyncLoopTarget, lock);
 }
 
-nsresult WorkerPrivate::DispatchLockHeld(already_AddRefed<WorkerRunnable> aRunnable,
-                                         nsIEventTarget* aSyncLoopTarget,
-                                         const MutexAutoLock& aProofOfLock) {
+nsresult WorkerPrivate::DispatchLockHeld(
+    already_AddRefed<WorkerRunnable> aRunnable, nsIEventTarget* aSyncLoopTarget,
+    const MutexAutoLock& aProofOfLock) {
   // May be called on any thread!
   RefPtr<WorkerRunnable> runnable(aRunnable);
 
@@ -1378,8 +1378,7 @@ nsresult WorkerPrivate::DispatchLockHeld(already_AddRefed<WorkerRunnable> aRunna
     // they should not be delivered to a frozen worker. But frozen workers
     // aren't drawing from the thread's main event queue anyway, only from
     // mControlQueue.
-    rv = mThread->DispatchAnyThread(WorkerThreadFriendKey(),
-                                    runnable.forget());
+    rv = mThread->DispatchAnyThread(WorkerThreadFriendKey(), runnable.forget());
   }
 
   if (NS_WARN_IF(NS_FAILED(rv))) {
@@ -2125,6 +2124,8 @@ WorkerPrivate::WorkerPrivate(WorkerPrivate* aParent,
   // that ThrottledEventQueue can only be created on the main thread at the
   // moment.
   if (aParent) {
+    mMainThreadEventTargetForMessaging =
+        aParent->mMainThreadEventTargetForMessaging;
     mMainThreadEventTarget = aParent->mMainThreadEventTarget;
     mMainThreadDebuggeeEventTarget = aParent->mMainThreadDebuggeeEventTarget;
     return;
@@ -2141,7 +2142,14 @@ WorkerPrivate::WorkerPrivate(WorkerPrivate* aParent,
 
   // Throttle events to the main thread using a ThrottledEventQueue specific to
   // this tree of worker threads.
-  mMainThreadEventTarget = ThrottledEventQueue::Create(target);
+  mMainThreadEventTargetForMessaging = ThrottledEventQueue::Create(target);
+  if (StaticPrefs::dom_worker_use_medium_high_event_queue()) {
+    mMainThreadEventTarget =
+        ThrottledEventQueue::Create(GetMainThreadSerialEventTarget(),
+                                    nsIRunnablePriority::PRIORITY_MEDIUMHIGH);
+  } else {
+    mMainThreadEventTarget = mMainThreadEventTargetForMessaging;
+  }
   mMainThreadDebuggeeEventTarget = ThrottledEventQueue::Create(target);
   if (IsParentWindowPaused() || IsFrozen()) {
     MOZ_ALWAYS_SUCCEEDS(mMainThreadDebuggeeEventTarget->SetIsPaused(true));
@@ -2254,9 +2262,7 @@ already_AddRefed<WorkerPrivate> WorkerPrivate::Constructor(
   return worker.forget();
 }
 
-nsresult
-WorkerPrivate::SetIsDebuggerReady(bool aReady)
-{
+nsresult WorkerPrivate::SetIsDebuggerReady(bool aReady) {
   AssertIsOnParentThread();
   MutexAutoLock lock(mMutex);
 
@@ -2750,7 +2756,7 @@ void WorkerPrivate::DoRunLoop(JSContext* aCx) {
     // If the worker thread is spamming the main thread faster than it can
     // process the work, then pause the worker thread until the main thread
     // catches up.
-    size_t queuedEvents = mMainThreadEventTarget->Length() +
+    size_t queuedEvents = mMainThreadEventTargetForMessaging->Length() +
                           mMainThreadDebuggeeEventTarget->Length();
     if (queuedEvents > 5000) {
       // Note, postMessage uses mMainThreadDebuggeeEventTarget!
@@ -2783,6 +2789,22 @@ void WorkerPrivate::AfterProcessNextEvent() {
   MOZ_ASSERT(CycleCollectedJSContext::Get()->RecursionDepth());
 }
 
+nsIEventTarget* WorkerPrivate::MainThreadEventTargetForMessaging() {
+  return mMainThreadEventTargetForMessaging;
+}
+
+nsresult WorkerPrivate::DispatchToMainThreadForMessaging(nsIRunnable* aRunnable,
+                                                         uint32_t aFlags) {
+  nsCOMPtr<nsIRunnable> r = aRunnable;
+  return DispatchToMainThreadForMessaging(r.forget(), aFlags);
+}
+
+nsresult WorkerPrivate::DispatchToMainThreadForMessaging(
+    already_AddRefed<nsIRunnable> aRunnable, uint32_t aFlags) {
+  return mMainThreadEventTargetForMessaging->Dispatch(std::move(aRunnable),
+                                                      aFlags);
+}
+
 nsIEventTarget* WorkerPrivate::MainThreadEventTarget() {
   return mMainThreadEventTarget;
 }
@@ -3148,9 +3170,12 @@ void WorkerPrivate::ScheduleDeletion(WorkerRanOrNot aRanOrNot) {
       NS_WARNING("Failed to dispatch runnable!");
     }
   } else {
+    // Note, this uses the lower priority DispatchToMainThreadForMessaging for
+    // dispatching TopLevelWorkerFinishedRunnable to the main thread so that
+    // other relevant runnables are guaranteed to run before it.
     RefPtr<TopLevelWorkerFinishedRunnable> runnable =
         new TopLevelWorkerFinishedRunnable(this);
-    if (NS_FAILED(DispatchToMainThread(runnable.forget()))) {
+    if (NS_FAILED(DispatchToMainThreadForMessaging(runnable.forget()))) {
       NS_WARNING("Failed to dispatch runnable!");
     }
   }

dom/workers/WorkerPrivate.h

@@ -401,6 +401,15 @@ class WorkerPrivate : public RelativeTimeline {
   // Get the event target to use when dispatching to the main thread
   // from this Worker thread.  This may be the main thread itself or
   // a ThrottledEventQueue to the main thread.
+  nsIEventTarget* MainThreadEventTargetForMessaging();
+
+  nsresult DispatchToMainThreadForMessaging(
+      nsIRunnable* aRunnable, uint32_t aFlags = NS_DISPATCH_NORMAL);
+
+  nsresult DispatchToMainThreadForMessaging(
+      already_AddRefed<nsIRunnable> aRunnable,
+      uint32_t aFlags = NS_DISPATCH_NORMAL);
+
   nsIEventTarget* MainThreadEventTarget();
 
   nsresult DispatchToMainThread(nsIRunnable* aRunnable,
@@ -973,6 +982,7 @@ class WorkerPrivate : public RelativeTimeline {
   PRThread* mPRThread;
 
   // Accessed from main thread
+  RefPtr<ThrottledEventQueue> mMainThreadEventTargetForMessaging;
   RefPtr<ThrottledEventQueue> mMainThreadEventTarget;
 
   // Accessed from worker thread and destructing thread

dom/workers/WorkerRunnable.cpp

@@ -619,7 +619,10 @@ bool WorkerProxyToMainThreadRunnable::Dispatch(WorkerPrivate* aWorkerPrivate) {
   MOZ_ASSERT(!mWorkerRef);
   mWorkerRef = new ThreadSafeWorkerRef(workerRef);
 
-  if (NS_WARN_IF(NS_FAILED(aWorkerPrivate->DispatchToMainThread(this)))) {
+  if (ForMessaging()
+          ? NS_WARN_IF(NS_FAILED(
+                aWorkerPrivate->DispatchToMainThreadForMessaging(this)))
+          : NS_WARN_IF(NS_FAILED(aWorkerPrivate->DispatchToMainThread(this)))) {
     ReleaseWorker();
     RunBackOnWorkerThreadForCleanup(aWorkerPrivate);
     return false;

dom/workers/WorkerRunnable.h

@@ -397,6 +397,8 @@ class WorkerProxyToMainThreadRunnable : public Runnable {
  public:
   bool Dispatch(WorkerPrivate* aWorkerPrivate);
 
+  virtual bool ForMessaging() const { return false; }
+
  private:
   NS_IMETHOD Run() override;
 

dom/workers/WorkerScope.cpp

@@ -661,7 +661,7 @@ void ServiceWorkerGlobalScope::SetOnfetch(
   if (aCallback) {
     if (mWorkerPrivate->WorkerScriptExecutedSuccessfully()) {
       RefPtr<Runnable> r = new ReportFetchListenerWarningRunnable(mScope);
-      mWorkerPrivate->DispatchToMainThread(r.forget());
+      mWorkerPrivate->DispatchToMainThreadForMessaging(r.forget());
     }
     mWorkerPrivate->SetFetchHandlerWasAdded();
   }
@@ -678,7 +678,7 @@ void ServiceWorkerGlobalScope::EventListenerAdded(nsAtom* aType) {
 
   if (mWorkerPrivate->WorkerScriptExecutedSuccessfully()) {
     RefPtr<Runnable> r = new ReportFetchListenerWarningRunnable(mScope);
-    mWorkerPrivate->DispatchToMainThread(r.forget());
+    mWorkerPrivate->DispatchToMainThreadForMessaging(r.forget());
   }
 
   mWorkerPrivate->SetFetchHandlerWasAdded();

modules/libpref/init/StaticPrefList.h

@@ -469,6 +469,12 @@ VARCACHE_PREF(
   RelaxedAtomicUint32, 30000 /* 30 seconds */
 )
 
+VARCACHE_PREF(
+  "dom.worker.use_medium_high_event_queue",
+   dom_worker_use_medium_high_event_queue,
+  RelaxedAtomicBool, true
+)
+
 // Enable content type normalization of XHR uploads via MIME Sniffing standard
 // Disabled for now in bz1499136
 VARCACHE_PREF(

xpcom/threads/ThrottledEventQueue.cpp

@@ -62,21 +62,31 @@ class ThrottledEventQueue::Inner final : public nsISupports {
   // The runnable which is dispatched to the underlying base target.  Since
   // we only execute one event at a time we just re-use a single instance
   // of this class while there are events left in the queue.
-  class Executor final : public Runnable {
+  class Executor final : public Runnable, public nsIRunnablePriority {
     // The Inner whose runnables we execute. mInner->mExecutor points
     // to this executor, forming a reference loop.
     RefPtr<Inner> mInner;
 
+    ~Executor() = default;
+
    public:
     explicit Executor(Inner* aInner)
         : Runnable("ThrottledEventQueue::Inner::Executor"), mInner(aInner) {}
 
+    NS_DECL_ISUPPORTS_INHERITED
+
     NS_IMETHODIMP
     Run() override {
       mInner->ExecuteRunnable();
       return NS_OK;
     }
 
+    NS_IMETHODIMP
+    GetPriority(uint32_t* aPriority) override {
+      *aPriority = mInner->mPriority;
+      return NS_OK;
+    }
+
 #ifdef MOZ_COLLECTING_RUNNABLE_TELEMETRY
     NS_IMETHODIMP
     GetName(nsACString& aName) override { return mInner->CurrentName(aName); }
@@ -103,14 +113,17 @@ class ThrottledEventQueue::Inner final : public nsISupports {
   // Used from any thread; protected by mMutex.
   nsCOMPtr<nsIRunnable> mExecutor;
 
+  const uint32_t mPriority;
+
   // True if this queue is currently paused.
   // Used from any thread; protected by mMutex.
   bool mIsPaused;
 
-  explicit Inner(nsISerialEventTarget* aBaseTarget)
+  explicit Inner(nsISerialEventTarget* aBaseTarget, uint32_t aPriority)
       : mMutex("ThrottledEventQueue"),
         mIdleCondVar(mMutex, "ThrottledEventQueue:Idle"),
         mBaseTarget(aBaseTarget),
+        mPriority(aPriority),
         mIsPaused(false) {}
 
   ~Inner() {
@@ -231,12 +244,13 @@ class ThrottledEventQueue::Inner final : public nsISupports {
   }
 
  public:
-  static already_AddRefed<Inner> Create(nsISerialEventTarget* aBaseTarget) {
+  static already_AddRefed<Inner> Create(nsISerialEventTarget* aBaseTarget,
+                                        uint32_t aPriority) {
     MOZ_ASSERT(NS_IsMainThread());
     MOZ_ASSERT(ClearOnShutdown_Internal::sCurrentShutdownPhase ==
                ShutdownPhase::NotInShutdown);
 
-    RefPtr<Inner> ref = new Inner(aBaseTarget);
+    RefPtr<Inner> ref = new Inner(aBaseTarget, aPriority);
     return ref.forget();
   }
 
@@ -332,6 +346,9 @@ class ThrottledEventQueue::Inner final : public nsISupports {
 
 NS_IMPL_ISUPPORTS(ThrottledEventQueue::Inner, nsISupports);
 
+NS_IMPL_ISUPPORTS_INHERITED(ThrottledEventQueue::Inner::Executor, Runnable,
+                            nsIRunnablePriority)
+
 NS_IMPL_ISUPPORTS(ThrottledEventQueue, ThrottledEventQueue, nsIEventTarget,
                   nsISerialEventTarget);
 
@@ -341,11 +358,11 @@ ThrottledEventQueue::ThrottledEventQueue(already_AddRefed<Inner> aInner)
 }
 
 already_AddRefed<ThrottledEventQueue> ThrottledEventQueue::Create(
-    nsISerialEventTarget* aBaseTarget) {
+    nsISerialEventTarget* aBaseTarget, uint32_t aPriority) {
   MOZ_ASSERT(NS_IsMainThread());
   MOZ_ASSERT(aBaseTarget);
 
-  RefPtr<Inner> inner = Inner::Create(aBaseTarget);
+  RefPtr<Inner> inner = Inner::Create(aBaseTarget, aPriority);
 
   RefPtr<ThrottledEventQueue> ref = new ThrottledEventQueue(inner.forget());
   return ref.forget();

xpcom/threads/ThrottledEventQueue.h

@@ -68,7 +68,8 @@ class ThrottledEventQueue final : public nsISerialEventTarget {
  public:
   // Create a ThrottledEventQueue for the given target.
   static already_AddRefed<ThrottledEventQueue> Create(
-      nsISerialEventTarget* aBaseTarget);
+      nsISerialEventTarget* aBaseTarget,
+      uint32_t aPriority = nsIRunnablePriority::PRIORITY_NORMAL);
 
   // Determine if there are any events pending in the queue.
   bool IsEmpty() const;