Use FileDescriptorWatcher in AlarmTimer.

components/timers/alarm_timer_chromeos.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_TIMERS_ALARM_TIMER_CHROMEOS_H_
 #define COMPONENTS_TIMERS_ALARM_TIMER_CHROMEOS_H_
 
 #include <memory>
 
-#include "base/callback.h"
+#include "base/files/file_descriptor_watcher_posix.h"
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/weak_ptr.h"
+#include "base/threading/sequenced_task_runner_handle.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
+// 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
+// version 3.11 or higher. On all other platforms, the AlarmTimer behaves
 // exactly the same way as a regular Timer.
+//
+// An AlarmTimer instance can only be used from the sequence on which it was
+// instantiated. Start() and Stop() must be called from a thread that supports
+// FileDescriptorWatcher.
 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();
+  // Called when |alarm_fd_| is readable without blocking. Reads data from
+  // |alarm_fd_| and calls OnTimerFired().
+  void OnAlarmFdReadableWithoutBlocking();
 
-  // Will be called by the delegate to indicate that the timer has fired and
-  // that the user task should be run.
+  // Called when the timer fires. Runs the callback.
   void OnTimerFired();
 
-  // Called when |origin_message_loop_| will be destroyed.
-  void WillDestroyCurrentMessageLoop();
+  // 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 constructor actually tries
+  // to set it up.
+  bool CanWakeFromSuspend() const;
 
-  // Delegate that will manage actually setting the timer.
-  class Delegate;
-  scoped_refptr<Delegate> delegate_;
+  // Timer file descriptor.
+  const int alarm_fd_;
 
-  // Keeps track of the user task we want to run.  A new one is constructed
-  // every time Reset() is called.
+  // Watches |alarm_fd_|.
+  std::unique_ptr<base::FileDescriptorWatcher::Controller> alarm_fd_watcher_;
+
+  // Posts tasks to the sequence on which this AlarmTimer was instantiated.
+  const scoped_refptr<base::SequencedTaskRunner> origin_task_runner_ =
+      base::SequencedTaskRunnerHandle::Get();
+
+  // Keeps track of the user task we want to run. A new one is constructed every
+  // time Reset() is called.
   std::unique_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;
-  std::unique_ptr<MessageLoopObserver> message_loop_observer_;
-
+  // Used to invalidate pending callbacks.
   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_