components: Introduce AlarmTimer class and use it for GCM heartbeat

components/timer/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/timer/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/timer/rtc_alarm.h"
+
+namespace timer {
+
+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.
+  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 (!retain_user_task_)
+    user_task_.Reset();
+}
+
+void AlarmTimer::Reset() {
+  if (!can_wake_from_suspend_) {
+    base::Timer::Reset();
+    return;
+  }
+
+  DCHECK(!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 (delay_ == base::TimeDelta()) {

[Lei Zhang, 2014/10/21 22:34:11]

timer.cc uses "delay_ > TimeDelta::FromMicroseconds(0)" BTW.

[Chirantan Ekbote, 2014/10/21 22:52:21]

Ah ok.  Will fix in the next patch set.

[Daniel Erat, 2014/10/23 03:44:54]

TimeDelta() and TimeDelta::FromMicroseconds(0) are equivalent, right? is the
point that negative durations should be handled by this block as well?

[Chirantan Ekbote, 2014/10/23 23:53:30]

The documentation for timerfd_settime doesn't say how it handles negative
durations (it just says a non-zero duration will arm the timer) so I think it's
better to deal with it here.

+    desired_run_time_ = base::TimeTicks();
+    pending_task_.reset(new base::PendingTask(posted_from_, user_task_));
+  } else {
+    desired_run_time_ = base::TimeTicks::Now() + delay_;
+    pending_task_.reset(new base::PendingTask(
+        posted_from_, user_task_, desired_run_time_, true));
+  }
+  base::MessageLoop::current()->task_annotator()->DidQueueTask(
+      "AlarmTimer::Reset", *pending_task_);
+
+  // Now start up the timer.
+  delegate_->Reset(delay_);
+  is_running_ = true;
+}
+
+void AlarmTimer::WillDestroyCurrentMessageLoop() {
+  Stop();
+}
+
+void AlarmTimer::OnTimerFired() {
+  if (!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 (is_repeating_)
+    Reset();
+  else
+    Stop();
+
+  // Now run the user task.
+  base::MessageLoop::current()->task_annotator()->RunTask(
+      "AlarmTimer::Reset", "AlarmTimer::OnTimerFired", *pending_user_task);
+}
+
+}  // namespace timer