components: Introduce AlarmTimer class and use it for GCM heartbeat

components/timers/alarm_timer.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 "components/timers/alarm_timer.h"
+
+#include "base/bind.h"
+#include "base/bind_helpers.h"
+#include "base/files/file_util.h"
+#include "base/logging.h"
+#include "base/pending_task.h"
+#include "components/timers/rtc_alarm.h"
+
+namespace timers {
+
+AlarmTimer::AlarmTimer(bool retain_user_task, bool is_repeating)
+    : base::Timer(retain_user_task, is_repeating),
+      delegate_(new RtcAlarm()),
+      can_wake_from_suspend_(false),
+      origin_message_loop_(NULL),
+      weak_factory_(this) {
+  can_wake_from_suspend_ = delegate_->Init(weak_factory_.GetWeakPtr());
+}
+
+AlarmTimer::AlarmTimer(const tracked_objects::Location& posted_from,
+                       base::TimeDelta delay,
+                       const base::Closure& user_task,
+                       bool is_repeating)
+    : base::Timer(posted_from, delay, user_task, is_repeating),
+      delegate_(new RtcAlarm()),
+      can_wake_from_suspend_(false),
+      origin_message_loop_(NULL),
+      weak_factory_(this) {
+  can_wake_from_suspend_ = delegate_->Init(weak_factory_.GetWeakPtr());
+}
+
+AlarmTimer::~AlarmTimer() {
+  Stop();
+}
+
+void AlarmTimer::Stop() {
+  if (!can_wake_from_suspend_) {
+    base::Timer::Stop();
+    return;
+  }
+
+  // Clear the running flag, stop the delegate, and delete the pending task.
+  base::Timer::set_is_running(false);
+  delegate_->Stop();
+  pending_task_.reset();
+
+  // Stop is called when the AlarmTimer is destroyed so we need to remove
+  // ourselves as a MessageLoop::DestructionObserver to prevent a segfault
+  // later.
+  if (origin_message_loop_) {
+    origin_message_loop_->RemoveDestructionObserver(this);
+    origin_message_loop_ = NULL;
+  }
+
+  if (!base::Timer::retain_user_task())
+    base::Timer::set_user_task(base::Closure());
+}
+
+void AlarmTimer::Reset() {
+  if (!can_wake_from_suspend_) {
+    base::Timer::Reset();
+    return;
+  }
+
+  DCHECK(!base::Timer::user_task().is_null());
+  DCHECK(!origin_message_loop_ ||
+         origin_message_loop_->task_runner()->RunsTasksOnCurrentThread());
+
+  // Make sure that the timer will stop if the underlying message loop is
+  // destroyed.
+  if (!origin_message_loop_) {
+    origin_message_loop_ = base::MessageLoop::current();
+    origin_message_loop_->AddDestructionObserver(this);
+  }
+
+  // Set up the pending task.
+  if (base::Timer::GetCurrentDelay() > base::TimeDelta::FromMicroseconds(0)) {
+    base::Timer::set_desired_run_time(
+        base::TimeTicks::Now() + base::Timer::GetCurrentDelay());
+    pending_task_.reset(new base::PendingTask(base::Timer::posted_from(),
+                                              base::Timer::user_task(),
+                                              base::Timer::desired_run_time(),
+                                              true  /* nestable */));
+  } else {
+    base::Timer::set_desired_run_time(base::TimeTicks());
+    pending_task_.reset(new base::PendingTask(base::Timer::posted_from(),
+                                              base::Timer::user_task()));
+  }
+  base::MessageLoop::current()->task_annotator()->DidQueueTask(
+      "AlarmTimer::Reset", *pending_task_);
+
+  // Now start up the timer.
+  delegate_->Reset(base::Timer::GetCurrentDelay());
+  base::Timer::set_is_running(true);
+}
+
+void AlarmTimer::WillDestroyCurrentMessageLoop() {
+  Stop();
+}
+
+void AlarmTimer::OnTimerFired() {
+  if (!base::Timer::is_running())
+    return;
+
+  DCHECK(pending_task_.get());
+
+  // Take ownership of the pending user task, which is going to be cleared by
+  // the Stop() or Reset() functions below.
+  scoped_ptr<base::PendingTask> pending_user_task(pending_task_.Pass());
+
+  // Re-schedule or stop the timer as requested.
+  if (base::Timer::is_repeating())
+    Reset();
+  else
+    Stop();
+
+  // Now run the user task.
+  base::MessageLoop::current()->task_annotator()->RunTask(
+      "AlarmTimer::Reset", "AlarmTimer::OnTimerFired", *pending_user_task);
+}
+
+}  // namespace timers