scheduler: Implement task observers

content/renderer/scheduler/task_queue_manager.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/renderer/scheduler/task_queue_manager.h"
 
 #include <queue>
 
 #include "base/bind.h"
+#include "base/observer_list.h"
 #include "base/trace_event/trace_event.h"
 #include "base/trace_event/trace_event_argument.h"
 #include "cc/test/test_now_source.h"
 #include "content/renderer/scheduler/task_queue_selector.h"
 
 namespace {
 const int64_t kMaxTimeTicks = std::numeric_limits<int64>::max();
 }
 
 namespace content {
@@ skipping 386 matching lines @@
 void TaskQueueManager::ProcessTaskFromWorkQueue(size_t queue_index) {
   DCHECK(main_thread_checker_.CalledOnValidThread());
   internal::TaskQueue* queue = Queue(queue_index);
   base::PendingTask pending_task = queue->TakeTaskFromWorkQueue();
   if (!pending_task.nestable) {
     // Defer non-nestable work to the main task runner.  NOTE these tasks can be
     // arbitrarily delayed so the additional delay should not be a problem.
     main_task_runner_->PostNonNestableTask(pending_task.posted_from,
                                            pending_task.task);
   } else {
+    FOR_EACH_OBSERVER(base::MessageLoop::TaskObserver, task_observers_,

[alex clarke (OOO till 29th), 2015/02/13 11:02:07]

Aren't we risking a scenario like this:

base::MessageLoop::RunTask
FOR_EACH_OBSERVER(...)
task_annotator_.RunTask()
    ...
    TaskQueueManager::ProcessTaskFromWorkQueue
    FOR_EACH_OBSERVER(...)
    task_annotator_.RunTask()
        actual task runs
    FOR_EACH_OBSERVER(...)

    x 1-4
FOR_EACH_OBSERVER(...)

[Sami, 2015/02/13 12:09:09]

We talked about this offline. It should be fine because we're intercepting all
observers from Blink and those should be the only ones that matter w.r.t.
microtasks.

+                      WillProcessTask(pending_task));
     task_annotator_.RunTask("TaskQueueManager::PostTask",
                             "TaskQueueManager::RunTask", pending_task);
+    FOR_EACH_OBSERVER(base::MessageLoop::TaskObserver, task_observers_,
+                      DidProcessTask(pending_task));
   }
 }
 
 bool TaskQueueManager::RunsTasksOnCurrentThread() const {
   return main_task_runner_->RunsTasksOnCurrentThread();
 }
 
 bool TaskQueueManager::PostDelayedTask(
     const tracked_objects::Location& from_here,
     const base::Closure& task,
     base::TimeDelta delay) {
   DCHECK(delay > base::TimeDelta());
   return main_task_runner_->PostDelayedTask(from_here, task, delay);
 }
 
 void TaskQueueManager::SetQueueName(size_t queue_index, const char* name) {
   DCHECK(main_thread_checker_.CalledOnValidThread());
   internal::TaskQueue* queue = Queue(queue_index);
   queue->set_name(name);
 }
 
 void TaskQueueManager::SetWorkBatchSize(int work_batch_size) {
   DCHECK(main_thread_checker_.CalledOnValidThread());
   DCHECK_GE(work_batch_size, 1);
   work_batch_size_ = work_batch_size;
 }
 
+void TaskQueueManager::AddTaskObserver(
+    base::MessageLoop::TaskObserver* task_observer) {
+  DCHECK(main_thread_checker_.CalledOnValidThread());
+  task_observers_.AddObserver(task_observer);
+}
+
+void TaskQueueManager::RemoveTaskObserver(
+    base::MessageLoop::TaskObserver* task_observer) {
+  DCHECK(main_thread_checker_.CalledOnValidThread());
+  task_observers_.RemoveObserver(task_observer);
+}
+
 void TaskQueueManager::SetTimeSourceForTesting(
     scoped_refptr<cc::TestNowSource> time_source) {
   DCHECK(main_thread_checker_.CalledOnValidThread());
   time_source_ = time_source;
 }
 
 base::TimeTicks TaskQueueManager::Now() const {
   return UNLIKELY(time_source_) ? time_source_->Now() : base::TimeTicks::Now();
 }
 
 scoped_refptr<base::trace_event::ConvertableToTraceFormat>
 TaskQueueManager::AsValueWithSelectorResult(bool should_run,
                                             size_t selected_queue) const {
   DCHECK(main_thread_checker_.CalledOnValidThread());
   scoped_refptr<base::trace_event::TracedValue> state =
       new base::trace_event::TracedValue();
   state->BeginArray("queues");
   for (auto& queue : queues_)
     queue->AsValueInto(state.get());
   state->EndArray();
   state->BeginDictionary("selector");
   selector_->AsValueInto(state.get());
   state->EndDictionary();
   if (should_run)
     state->SetInteger("selected_queue", selected_queue);
   return state;
 }
 
 }  // namespace content