components: Introduce AlarmTimer class and use it for GCM heartbeat

base/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 "base/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"
+
+#if defined(OS_CHROMEOS)
+#include "base/timer/rtc_alarm_chromeos.h"
+#endif
+
+namespace base {
+
+namespace {
+
+// Default delegate for the alarm timer on non-Chrome OS systems.  Tells the
+// AlarmTimer class that it doesn't have the ability to wake the system from
+// suspend and that it should just behave as a regular Timer.
+class DefaultAlarmTimerDelegate : public base::AlarmTimer::Delegate {
+ public:
+  DefaultAlarmTimerDelegate() {}
+
+  virtual bool Init(base::WeakPtr<AlarmTimer> timer) override { return false; }
+  virtual void Stop() override {
+    NOTREACHED() << "Attempting to call Stop() on the default alarm timer "
+                 << "delegate";
+  }
+  virtual void Reset(base::TimeDelta delay) override {
+    NOTREACHED() << "Attempting to call Reset() on the default alarm timer "
+                 << "delegate";
+  }
+
+ protected:
+  virtual ~DefaultAlarmTimerDelegate() {}
+};
+
+}  // namespace
+
+AlarmTimer::AlarmTimer(bool retain_user_task, bool is_repeating)
+    : Timer(retain_user_task, is_repeating),
+#if defined(OS_CHROMEOS)
+      delegate_(new RtcAlarmChromeos()),
+#else
+      delegate_(new DefaultAlarmTimerDelegate()),
+#endif
+      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,
+                       TimeDelta delay,
+                       const Closure& user_task,
+                       bool is_repeating)
+    : Timer(posted_from, delay, user_task, is_repeating),
+#if defined(OS_CHROMEOS)

[Daniel Erat, 2014/10/15 15:04:22]

i don't have strong feelings here, but it might be nice to all of the post-Timer
initialization into a separate method so it isn't duplicated between the two
c'tors.

[Chirantan Ekbote, 2014/10/16 21:26:38]

Done.

+      delegate_(new RtcAlarmChromeos()),
+#else
+      delegate_(new DefaultAlarmTimerDelegate()),
+#endif
+      can_wake_from_suspend_(false),
+      origin_message_loop_(NULL),
+      weak_factory_(this) {
+  can_wake_from_suspend_ = delegate_->Init(weak_factory_.GetWeakPtr());
+}
+
+AlarmTimer::~AlarmTimer() {
+  Stop();
+}
+
+bool AlarmTimer::IsRunning() const {
+  if (!can_wake_from_suspend_)

[Daniel Erat, 2014/10/15 15:04:21]

nit:

  return can_wake_from_suspend_ ? is_running_ : Timer::IsRunning();

+    return Timer::IsRunning();
+
+  return is_running_;
+}
+
+TimeDelta AlarmTimer::GetCurrentDelay() const {
+  if (!can_wake_from_suspend_)

[Daniel Erat, 2014/10/15 15:04:21]

nit:

  return can_wake_from_suspend_ ? delay_ : Timer::GetCurrentDelay();

+    return Timer::GetCurrentDelay();
+
+  return delay_;
+}
+
+void AlarmTimer::Start(const tracked_objects::Location& posted_from,
+                       TimeDelta delay,
+                       const Closure& user_task) {
+  if (!can_wake_from_suspend_) {
+    Timer::Start(posted_from, delay, user_task);
+    return;
+  }
+
+  // This is identical to the implementation of Timer::Start but we have this
+  // one anyway for clarity.

[Daniel Erat, 2014/10/15 15:04:21]

not sure i understand this. if this method is identical to Timer::Start(), why
is it being overridden?

[Chirantan Ekbote, 2014/10/16 21:26:38]

It's being overridden so that someone reading the code doesn't have to look
through two files to see the whole implementation.  If it's ok to not override
these and just re-use the Timer implementation, then we can also get rid of
IsRunning() and GetCurrentDelay(), which is what I've done in the latest patch
set.

+  Timer::SetTaskInfo(posted_from, delay, user_task);
+  Reset();
+}
+
+void AlarmTimer::Stop() {
+  if (!can_wake_from_suspend_) {
+    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_) {
+    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_ = MessageLoop::current();
+    origin_message_loop_->AddDestructionObserver(this);
+  }
+
+  // Set up the pending task.
+  if (delay_ == TimeDelta()) {
+    desired_run_time_ = TimeTicks();
+    pending_task_.reset(new PendingTask(posted_from_, user_task_));
+  } else {
+    desired_run_time_ = TimeTicks::Now() + delay_;
+    pending_task_.reset(
+        new PendingTask(posted_from_, user_task_, desired_run_time_, true));
+  }
+  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<PendingTask> pending_user_task(pending_task_.Pass());
+
+  // Re-schedule or stop the timer as requested.
+  if (is_repeating_)
+    Reset();
+  else
+    Stop();
+
+  // Now lets run the user task.

[Daniel Erat, 2014/10/15 15:04:22]

nit: s/lets/let's/ or just delete that word

[Chirantan Ekbote, 2014/10/16 21:26:38]

Done.

+  MessageLoop::current()->task_annotator()->RunTask(
+      "AlarmTimer::Reset", "AlarmTimer::OnTimerFired", *pending_user_task);
+}
+
+}  // namespace base