C++ readability review

components/timers/alarm_timer_chromeos.h

Index: components/timers/alarm_timer_chromeos.h
diff --git a/components/timers/alarm_timer_chromeos.h b/components/timers/alarm_timer_chromeos.h
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+++ b/components/timers/alarm_timer_chromeos.h
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+// 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.
+
+#ifndef COMPONENTS_TIMERS_ALARM_TIMER_CHROMEOS_H_
+#define COMPONENTS_TIMERS_ALARM_TIMER_CHROMEOS_H_
+
+#include "base/callback.h"
+#include "base/macros.h"
+#include "base/memory/ref_counted.h"
+#include "base/memory/weak_ptr.h"
+#include "base/time/time.h"
+#include "base/timer/timer.h"
+
+namespace base {
+class MessageLoop;
+struct PendingTask;
+}
+
+namespace timers {
+// The class implements a timer that is capable of waking the system up from a
+// suspended state.  For example, this is useful for running tasks that are
+// needed for maintaining network connectivity, like sending heartbeat messages.
+// Currently, this feature is only available on Chrome OS systems running linux
+// version 3.11 or higher.  On all other platforms, the AlarmTimer behaves
+// exactly the same way as a regular Timer.
+class AlarmTimer : public base::Timer {
+ public:
+  ~AlarmTimer() override;
+
+  bool can_wake_from_suspend() const { return can_wake_from_suspend_; }
+
+  // Sets a hook that will be called when the timer fires and a task has been
+  // queued on |origin_message_loop_|.  Used by tests to wait until a task is
+  // pending in the MessageLoop.
+  void SetTimerFiredCallbackForTest(base::Closure test_callback);
+
+  // Timer overrides.
+  void Stop() override;
+  void Reset() override;
+
+ protected:
+  // The constructors for this class are protected because consumers should
+  // instantiate one of the specialized sub-classes defined below instead.
+  AlarmTimer(bool retain_user_task, bool is_repeating);
+  AlarmTimer(const tracked_objects::Location& posted_from,
+             base::TimeDelta delay,
+             const base::Closure& user_task,
+             bool is_repeating);
+
+ private:
+  // Common initialization that must be performed by both constructors.  This
+  // really should live in a delegated constructor but the way base::Timer's
+  // constructors are written makes it really hard to do so.
+  void Init();
+
+  // Will be called by the delegate to indicate that the timer has fired and
+  // that the user task should be run.
+  void OnTimerFired();
+
+  // Called when |origin_message_loop_| will be destroyed.
+  void WillDestroyCurrentMessageLoop();
+
+  // Delegate that will manage actually setting the timer.
+  class Delegate;
+  scoped_refptr<Delegate> delegate_;
+
+  // Keeps track of the user task we want to run.  A new one is constructed
+  // every time Reset() is called.
+  scoped_ptr<base::PendingTask> pending_task_;
+
+  // Tracks whether the timer has the ability to wake the system up from
+  // suspend.  This is a runtime check because we won't know if the system
+  // supports being woken up from suspend until the delegate actually tries to
+  // set it up.
+  bool can_wake_from_suspend_;
+
+  // Pointer to the message loop that started the timer.  Used to track the
+  // destruction of that message loop.
+  base::MessageLoop* origin_message_loop_;
+
+  // Observes |origin_message_loop_| and informs this class if it will be
+  // destroyed.
+  class MessageLoopObserver;
+  scoped_ptr<MessageLoopObserver> message_loop_observer_;
+
+  base::WeakPtrFactory<AlarmTimer> weak_factory_;
+
+  DISALLOW_COPY_AND_ASSIGN(AlarmTimer);
+};
+
+// As its name suggests, a OneShotAlarmTimer runs a given task once.  It does
+// not remember the task that was given to it after it has fired and does not
+// repeat.  Useful for fire-and-forget tasks.
+class OneShotAlarmTimer : public AlarmTimer {
+ public:
+  // Constructs a basic OneShotAlarmTimer.  An AlarmTimer constructed this way
+  // requires that Start() is called before Reset() is called.
+  OneShotAlarmTimer();
+  ~OneShotAlarmTimer() override;
+};
+
+// A RepeatingAlarmTimer takes a task and delay and repeatedly runs the task
+// using the specified delay as an interval between the runs until it is
+// explicitly stopped.  It remembers both the task and the delay it was given
+// after it fires.
+class RepeatingAlarmTimer : public AlarmTimer {
+ public:
+  // Constructs a basic RepeatingAlarmTimer.  An AlarmTimer constructed this way
+  // requires that Start() is called before Reset() is called.
+  RepeatingAlarmTimer();
+
+  // Constructs a RepeatingAlarmTimer with pre-populated parameters but does not
+  // start it.  Useful if |user_task| or |delay| are not going to change.
+  // Reset() can be called immediately after constructing an AlarmTimer in this
+  // way.
+  RepeatingAlarmTimer(const tracked_objects::Location& posted_from,
+                      base::TimeDelta delay,
+                      const base::Closure& user_task);
+
+  ~RepeatingAlarmTimer() override;
+};
+
+// A SimpleAlarmTimer only fires once but remembers the task that it was given
+// even after it has fired.  Useful if you want to run the same task multiple
+// times but not at a regular interval.
+class SimpleAlarmTimer : public AlarmTimer {
+ public:
+  // Constructs a basic SimpleAlarmTimer.  An AlarmTimer constructed this way
+  // requires that Start() is called before Reset() is called.
+  SimpleAlarmTimer();
+
+  // Constructs a SimpleAlarmTimer with pre-populated parameters but does not
+  // start it.  Useful if |user_task| or |delay| are not going to change.
+  // Reset() can be called immediately after constructing an AlarmTimer in this
+  // way.
+  SimpleAlarmTimer(const tracked_objects::Location& posted_from,
+                   base::TimeDelta delay,
+                   const base::Closure& user_task);
+
+  ~SimpleAlarmTimer() override;
+};
+
+}  // namespace timers
+
+#endif  // COMPONENTS_TIMERS_ALARM_TIMER_CHROMEOS_H_