scheduler: Implement task observers

content/renderer/scheduler/webthread_impl_for_scheduler.cc

+// Copyright 2015 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/webthread_impl_for_scheduler.h"
+
+#include "content/renderer/scheduler/renderer_scheduler.h"
+#include "third_party/WebKit/public/platform/WebTraceLocation.h"
+
+namespace content {
+namespace internal {
+
+// Observes tasks both from a MessageLoop and a RendererScheduler which is
+// driven by that MessageLoop and filters out redundant task observer
+// notifications.
+class NestedTaskObserver {
+ public:
+  NestedTaskObserver(base::MessageLoop* message_loop,
+                     RendererScheduler* scheduler,
+                     blink::WebThread::TaskObserver* client_observer)
+      : message_loop_(message_loop),
+        scheduler_(scheduler),
+        client_observer_(client_observer),
+        message_loop_observer_(this),
+        scheduler_observer_(this),
+        inside_task_(false) {
+    message_loop_->AddTaskObserver(&message_loop_observer_);
+    scheduler_->AddTaskObserver(&scheduler_observer_);
+  }
+
+  ~NestedTaskObserver() {
+    message_loop_->RemoveTaskObserver(&message_loop_observer_);
+    scheduler_->RemoveTaskObserver(&scheduler_observer_);
+  }
+
+ private:
+  class MessageLoopTaskObserver : public base::MessageLoop::TaskObserver {
+   public:
+    MessageLoopTaskObserver(NestedTaskObserver* parent) : parent_(parent) {}
+
+    void WillProcessTask(const base::PendingTask& pending_task) override {
+      parent_->WillProcessTask();
+    }
+
+    void DidProcessTask(const base::PendingTask& pending_task) override {
+      parent_->DidProcessTask();
+    }
+
+   private:
+    NestedTaskObserver* parent_;
+  };
+
+  class SchedulerTaskObserver : public base::MessageLoop::TaskObserver {
+   public:
+    SchedulerTaskObserver(NestedTaskObserver* parent) : parent_(parent) {}
+
+    void WillProcessTask(const base::PendingTask& pending_task) override {
+      parent_->WillProcessTask();
+    }
+
+    void DidProcessTask(const base::PendingTask& pending_task) override {
+      parent_->DidProcessTask();
+    }
+
+   private:
+    NestedTaskObserver* parent_;
+  };
+
+  void WillProcessTask() {
+    // Don't filter out callbacks in nested message loops to ensure the client
+    // sees at least the same callbacks as without the scheduler.
+    if (message_loop_->IsNested()) {
+      client_observer_->willProcessTask();
+      return;
+    }
+    if (!inside_task_) {
+      inside_task_ = true;
+      client_observer_->willProcessTask();
+    }
+  }
+
+  void DidProcessTask() {
+    if (message_loop_->IsNested()) {
+      client_observer_->didProcessTask();
+      return;
+    }
+    if (inside_task_) {
+      inside_task_ = false;
+      client_observer_->didProcessTask();
+    }
+  }
+
+  base::MessageLoop* message_loop_;                  // Not owned.
+  RendererScheduler* scheduler_;                     // Not owned.
+  blink::WebThread::TaskObserver* client_observer_;  // Not owned.
+  MessageLoopTaskObserver message_loop_observer_;
+  SchedulerTaskObserver scheduler_observer_;
+
+  bool inside_task_;
+
+  DISALLOW_COPY_AND_ASSIGN(NestedTaskObserver);
+};
+}  // namespace internal
+
+WebThreadImplForScheduler::WebThreadImplForScheduler(
+    RendererScheduler* scheduler)
+    : task_runner_(scheduler->DefaultTaskRunner()),
+      scheduler_(scheduler),
+      thread_id_(base::PlatformThread::CurrentId()) {
+}
+
+WebThreadImplForScheduler::~WebThreadImplForScheduler() {
+}
+
+blink::PlatformThreadId WebThreadImplForScheduler::threadId() const {
+  return thread_id_;
+}
+
+base::MessageLoop* WebThreadImplForScheduler::MessageLoop() const {
+  DCHECK(isCurrentThread());
+  return base::MessageLoop::current();
+}
+
+base::SingleThreadTaskRunner* WebThreadImplForScheduler::TaskRunner() const {
+  return task_runner_.get();
+}
+
+void WebThreadImplForScheduler::addTaskObserver(TaskObserver* observer) {
+  CHECK(isCurrentThread());
+  if (nested_task_observer_map_.contains(observer))
+    return;
+  nested_task_observer_map_.add(
+      observer, make_scoped_ptr(new internal::NestedTaskObserver(
+                    MessageLoop(), scheduler_, observer)));
+}
+
+void WebThreadImplForScheduler::removeTaskObserver(TaskObserver* observer) {
+  nested_task_observer_map_.erase(observer);
+}
+
+}  // namespace content