Worker: Introduce per-global-scope task scheduler

third_party/WebKit/Source/core/workers/WorkerEventQueue.cpp

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 #include "core/workers/WorkerEventQueue.h"
 
+#include "core/dom/TaskRunnerHelper.h"
 #include "core/events/Event.h"
 #include "core/probe/CoreProbes.h"
 #include "core/workers/WorkerGlobalScope.h"
 #include "core/workers/WorkerThread.h"
 
 namespace blink {
 
 WorkerEventQueue* WorkerEventQueue::Create(
     WorkerGlobalScope* worker_global_scope) {
   return new WorkerEventQueue(worker_global_scope);
@@ skipping 11 matching lines @@
   visitor->Trace(pending_events_);
   EventQueue::Trace(visitor);
 }
 
 bool WorkerEventQueue::EnqueueEvent(Event* event) {
   if (is_closed_)
     return false;
   probe::AsyncTaskScheduled(event->target()->GetExecutionContext(),
                             event->type(), event);
   pending_events_.insert(event);
-  worker_global_scope_->GetThread()->PostTask(
-      BLINK_FROM_HERE,
-      WTF::Bind(&WorkerEventQueue::DispatchEvent, WrapPersistent(this),
-                WrapWeakPersistent(event)));
+  // This queue is unthrottled because throttling event tasks may break existing
+  // web pages. For example, throttling IndexedDB events may break scenarios
+  // where several tabs, some of which are backgrounded, access the same
+  // database concurrently. See also comments in the ctor of
+  // DOMWindowEventQueueTimer.
+  // TODO(nhiroki): Callers of enqueueEvent() should specify the task type.
+  TaskRunnerHelper::Get(TaskType::kUnthrottled, worker_global_scope_.Get())
+      ->PostTask(BLINK_FROM_HERE,
+                 WTF::Bind(&WorkerEventQueue::DispatchEvent,
+                           WrapPersistent(this), WrapWeakPersistent(event)));

[haraken, 2017/04/17 14:49:52]

Not related to this CL, do you know why we're using a weak persistent for event?
I think it can be a normal persistent because the event is anyway kept alive by
pending_events_ until DispatchEvent runs.

[nhiroki, 2017/04/18 05:34:38]

It was introduced by https://codereview.chromium.org/2209613002

According to the CL description, it seems to be used for cancelling the event.
Now we could replace it with PostCancellableTask. I'll try it in a separate CL.

   return true;
 }
 
 bool WorkerEventQueue::CancelEvent(Event* event) {
   if (!RemoveEvent(event))
     return false;
   probe::AsyncTaskCanceled(event->target()->GetExecutionContext(), event);
   return true;
 }
 
@@ skipping 14 matching lines @@
 
 void WorkerEventQueue::DispatchEvent(Event* event) {
   if (!event || !RemoveEvent(event))
     return;
 
   probe::AsyncTask async_task(worker_global_scope_, event);
   event->target()->DispatchEvent(event);
 }
 
 }  // namespace blink