C++ readability review

components/timers/rtc_alarm.h

-// 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_TIMER_RTC_ALARM_H_
-#define COMPONENTS_TIMER_RTC_ALARM_H_
-
-#include "base/macros.h"
-#include "base/memory/ref_counted.h"
-#include "base/memory/scoped_ptr.h"
-#include "base/memory/weak_ptr.h"
-#include "base/message_loop/message_loop.h"
-#include "base/time/time.h"
-#include "components/timers/alarm_timer.h"
-
-namespace base {
-class MessageLoopProxy;
-}
-
-namespace timers {
-// This class manages a Real Time Clock (RTC) alarm, a feature that is available
-// from linux version 3.11 onwards.  It creates a file descriptor for the RTC
-// alarm timer and then watches that file descriptor to see when it can be read
-// without blocking, indicating that the timer has fired.
-//
-// A major problem for this class is that watching file descriptors is only
-// available on a MessageLoopForIO but there is no guarantee the timer is going
-// to be created on one.  To get around this, the timer has a dedicated thread
-// with a MessageLoopForIO that posts tasks back to the thread that started the
-// timer.
-//
-// This class is designed to work together with the AlarmTimer class and is
-// tested through the AlarmTimer unit tests.  DO NOT TRY TO USE THIS CLASS
-// DIRECTLY.  Or use it anyway, I'm a comment not a cop.
-class RtcAlarm : public AlarmTimer::Delegate,
-                 public base::MessageLoopForIO::Watcher {
- public:
-  RtcAlarm();
-
-  // AlarmTimer::Delegate overrides.
-  bool Init(base::WeakPtr<AlarmTimer> timer) override;
-  void Stop() override;
-  void Reset(base::TimeDelta delay) override;
-
-  // base::MessageLoopForIO::Watcher overrides.
-  void OnFileCanReadWithoutBlocking(int fd) override;
-  void OnFileCanWriteWithoutBlocking(int fd) override;
-
- protected:
-  // Needs to be protected because AlarmTimer::Delegate is a refcounted class.
-  ~RtcAlarm() override;
-
- private:
-  // Actually performs the system calls to set up the timer.  This must be
-  // called on a MessageLoopForIO.
-  void ResetImpl(base::TimeDelta delay, int event_id);
-
-  // Callback that is run when the timer fires.  Must be run on
-  // |origin_message_loop_|.
-  void OnTimerFired(int event_id);
-
-  // File descriptor associated with the alarm timer.
-  int alarm_fd_;
-
-  // Message loop which initially started the timer.
-  scoped_refptr<base::MessageLoopProxy> origin_message_loop_;
-
-  // The parent timer that should be informed when the timer fires.  We may end
-  // up outliving the parent so we need to ensure the reference is valid before
-  // we try to call it.
-  base::WeakPtr<AlarmTimer> parent_;
-
-  // Manages watching file descriptors.
-  scoped_ptr<base::MessageLoopForIO::FileDescriptorWatcher> fd_watcher_;
-
-  // These two variables are used for coordinating between the thread that
-  // started the timer and the IO thread being used to watch the timer file
-  // descriptor.  When Reset() is called, the original thread increments
-  // |origin_event_id_| and binds its value to ResetImpl(), which gets posted to
-  // the IO thread.  When the IO thread runs, it saves this value in
-  // |io_event_id_|.  Later, when the timer fires, the IO thread binds the value
-  // of |io_event_id_| to OnTimerFired() and posts it to the original thread.
-  // When the original thread runs OnTimerFired(), it calls
-  // parent_->OnTimerFired() only if |origin_event_id_| matches the event id
-  // that was passed in to it.  This is used to get around a race condition
-  // where the user resets the timer on the original thread, while the event is
-  // being fired on the IO thread at the same time.
-  int origin_event_id_;
-  int io_event_id_;
-
-  DISALLOW_COPY_AND_ASSIGN(RtcAlarm);
-};
-
-}  // namespace timers
-#endif  // COMPONENTS_TIMER_RTC_ALARM_H_