Import chromium-64.0.3282.119

base/timer/timer.h

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+// Copyright (c) 2012 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.
+
+// OneShotTimer and RepeatingTimer provide a simple timer API.  As the names
+// suggest, OneShotTimer calls you back once after a time delay expires.
+// RepeatingTimer on the other hand calls you back periodically with the
+// prescribed time interval.
+//
+// OneShotTimer and RepeatingTimer both cancel the timer when they go out of
+// scope, which makes it easy to ensure that you do not get called when your
+// object has gone out of scope.  Just instantiate a OneShotTimer or
+// RepeatingTimer as a member variable of the class for which you wish to
+// receive timer events.
+//
+// Sample RepeatingTimer usage:
+//
+//   class MyClass {
+//    public:
+//     void StartDoingStuff() {
+//       timer_.Start(FROM_HERE, TimeDelta::FromSeconds(1),
+//                    this, &MyClass::DoStuff);
+//     }
+//     void StopDoingStuff() {
+//       timer_.Stop();
+//     }
+//    private:
+//     void DoStuff() {
+//       // This method is called every second to do stuff.
+//       ...
+//     }
+//     base::RepeatingTimer timer_;
+//   };
+//
+// Both OneShotTimer and RepeatingTimer also support a Reset method, which
+// allows you to easily defer the timer event until the timer delay passes once
+// again.  So, in the above example, if 0.5 seconds have already passed,
+// calling Reset on |timer_| would postpone DoStuff by another 1 second.  In
+// other words, Reset is shorthand for calling Stop and then Start again with
+// the same arguments.
+//
+// These APIs are not thread safe. All methods must be called from the same
+// sequence (not necessarily the construction sequence), except for the
+// destructor and SetTaskRunner().
+// - The destructor may be called from any sequence when the timer is not
+// running and there is no scheduled task active, i.e. when Start() has never
+// been called or after AbandonAndStop() has been called.
+// - SetTaskRunner() may be called from any sequence when the timer is not
+// running, i.e. when Start() has never been called or Stop() has been called
+// since the last Start().
+//
+// By default, the scheduled tasks will be run on the same sequence that the
+// Timer was *started on*, but this can be changed *prior* to Start() via
+// SetTaskRunner().
+
+#ifndef BASE_TIMER_TIMER_H_
+#define BASE_TIMER_TIMER_H_
+
+// IMPORTANT: If you change timer code, make sure that all tests (including
+// disabled ones) from timer_unittests.cc pass locally. Some are disabled
+// because they're flaky on the buildbot, but when you run them locally you
+// should be able to tell the difference.
+
+#include <memory>
+
+#include "base/base_export.h"
+#include "base/bind.h"
+#include "base/bind_helpers.h"
+#include "base/callback.h"
+#include "base/location.h"
+#include "base/macros.h"
+#include "base/sequence_checker_impl.h"
+#include "base/sequenced_task_runner.h"
+#include "base/time/time.h"
+
+namespace base {
+
+class BaseTimerTaskInternal;
+class TickClock;
+
+// TODO(gab): Removing this fwd-decl causes IWYU failures in other headers,
+// remove it in a follow- up CL.
+class SingleThreadTaskRunner;
+
+//-----------------------------------------------------------------------------
+// This class wraps TaskRunner::PostDelayedTask to manage delayed and repeating
+// tasks. See meta comment above for thread-safety requirements.
+//
+class BASE_EXPORT Timer {
+ public:
+  // Construct a timer in repeating or one-shot mode. Start must be called later
+  // to set task info. |retain_user_task| determines whether the user_task is
+  // retained or reset when it runs or stops. If |tick_clock| is provided, it is
+  // used instead of TimeTicks::Now() to get TimeTicks when scheduling tasks.
+  Timer(bool retain_user_task, bool is_repeating);
+  Timer(bool retain_user_task, bool is_repeating, TickClock* tick_clock);
+
+  // Construct a timer with retained task info. If |tick_clock| is provided, it
+  // is used instead of TimeTicks::Now() to get TimeTicks when scheduling tasks.
+  Timer(const Location& posted_from,
+        TimeDelta delay,
+        const base::Closure& user_task,
+        bool is_repeating);
+  Timer(const Location& posted_from,
+        TimeDelta delay,
+        const base::Closure& user_task,
+        bool is_repeating,
+        TickClock* tick_clock);
+
+  virtual ~Timer();
+
+  // Returns true if the timer is running (i.e., not stopped).
+  virtual bool IsRunning() const;
+
+  // Returns the current delay for this timer.
+  virtual TimeDelta GetCurrentDelay() const;
+
+  // Set the task runner on which the task should be scheduled. This method can
+  // only be called before any tasks have been scheduled. If |task_runner| runs
+  // tasks on a different sequence than the sequence owning this Timer,
+  // |user_task_| will be posted to it when the Timer fires (note that this
+  // means |user_task_| can run after ~Timer() and should support that).
+  void SetTaskRunner(scoped_refptr<SequencedTaskRunner> task_runner);
+
+  // Start the timer to run at the given |delay| from now. If the timer is
+  // already running, it will be replaced to call the given |user_task|.
+  virtual void Start(const Location& posted_from,
+                     TimeDelta delay,
+                     const base::Closure& user_task);
+
+  // Call this method to stop and cancel the timer.  It is a no-op if the timer
+  // is not running.
+  virtual void Stop();
+
+  // Stop running task (if any) and abandon scheduled task (if any).
+  void AbandonAndStop() {
+    AbandonScheduledTask();
+
+    Stop();
+    // No more member accesses here: |this| could be deleted at this point.
+  }
+
+  // Call this method to reset the timer delay. The |user_task_| must be set. If
+  // the timer is not running, this will start it by posting a task.
+  virtual void Reset();
+
+  const base::Closure& user_task() const { return user_task_; }
+  const TimeTicks& desired_run_time() const { return desired_run_time_; }
+
+ protected:
+  // Returns the current tick count.
+  TimeTicks Now() const;
+
+  void set_user_task(const Closure& task) { user_task_ = task; }
+  void set_desired_run_time(TimeTicks desired) { desired_run_time_ = desired; }
+  void set_is_running(bool running) { is_running_ = running; }
+
+  const Location& posted_from() const { return posted_from_; }
+  bool retain_user_task() const { return retain_user_task_; }
+  bool is_repeating() const { return is_repeating_; }
+  bool is_running() const { return is_running_; }
+
+ private:
+  friend class BaseTimerTaskInternal;
+
+  // Allocates a new |scheduled_task_| and posts it on the current sequence with
+  // the given |delay|. |scheduled_task_| must be null. |scheduled_run_time_|
+  // and |desired_run_time_| are reset to Now() + delay.
+  void PostNewScheduledTask(TimeDelta delay);
+
+  // Returns the task runner on which the task should be scheduled. If the
+  // corresponding |task_runner_| field is null, the task runner for the current
+  // sequence is returned.
+  scoped_refptr<SequencedTaskRunner> GetTaskRunner();
+
+  // Disable |scheduled_task_| and abandon it so that it no longer refers back
+  // to this object.
+  void AbandonScheduledTask();
+
+  // Called by BaseTimerTaskInternal when the delayed task fires.
+  void RunScheduledTask();
+
+  // When non-null, the |scheduled_task_| was posted to call RunScheduledTask()
+  // at |scheduled_run_time_|.
+  BaseTimerTaskInternal* scheduled_task_;
+
+  // The task runner on which the task should be scheduled. If it is null, the
+  // task runner for the current sequence will be used.
+  scoped_refptr<SequencedTaskRunner> task_runner_;
+
+  // Location in user code.
+  Location posted_from_;
+  // Delay requested by user.
+  TimeDelta delay_;
+  // |user_task_| is what the user wants to be run at |desired_run_time_|.
+  base::Closure user_task_;
+
+  // The time at which |scheduled_task_| is expected to fire. This time can be a
+  // "zero" TimeTicks if the task must be run immediately.
+  TimeTicks scheduled_run_time_;
+
+  // The desired run time of |user_task_|. The user may update this at any time,
+  // even if their previous request has not run yet. If |desired_run_time_| is
+  // greater than |scheduled_run_time_|, a continuation task will be posted to
+  // wait for the remaining time. This allows us to reuse the pending task so as
+  // not to flood the delayed queues with orphaned tasks when the user code
+  // excessively Stops and Starts the timer. This time can be a "zero" TimeTicks
+  // if the task must be run immediately.
+  TimeTicks desired_run_time_;
+
+  // Timer isn't thread-safe and must only be used on its origin sequence
+  // (sequence on which it was started). Once fully Stop()'ed it may be
+  // destroyed or restarted on another sequence.
+  SequenceChecker origin_sequence_checker_;
+
+  // Repeating timers automatically post the task again before calling the task
+  // callback.
+  const bool is_repeating_;
+
+  // If true, hold on to the |user_task_| closure object for reuse.
+  const bool retain_user_task_;
+
+  // The tick clock used to calculate the run time for scheduled tasks.
+  TickClock* const tick_clock_;
+
+  // If true, |user_task_| is scheduled to run sometime in the future.
+  bool is_running_;
+
+  DISALLOW_COPY_AND_ASSIGN(Timer);
+};
+
+//-----------------------------------------------------------------------------
+// This class is an implementation detail of OneShotTimer and RepeatingTimer.
+// Please do not use this class directly.
+class BaseTimerMethodPointer : public Timer {
+ public:
+  // This is here to work around the fact that Timer::Start is "hidden" by the
+  // Start definition below, rather than being overloaded.
+  // TODO(tim): We should remove uses of BaseTimerMethodPointer::Start below
+  // and convert callers to use the base::Closure version in Timer::Start,
+  // see bug 148832.
+  using Timer::Start;
+
+  enum RepeatMode { ONE_SHOT, REPEATING };
+  BaseTimerMethodPointer(RepeatMode mode, TickClock* tick_clock)
+      : Timer(mode == REPEATING, mode == REPEATING, tick_clock) {}
+
+  // Start the timer to run at the given |delay| from now. If the timer is
+  // already running, it will be replaced to call a task formed from
+  // |reviewer->*method|.
+  template <class Receiver>
+  void Start(const Location& posted_from,
+             TimeDelta delay,
+             Receiver* receiver,
+             void (Receiver::*method)()) {
+    Timer::Start(posted_from, delay,
+                 base::Bind(method, base::Unretained(receiver)));
+  }
+};
+
+//-----------------------------------------------------------------------------
+// A simple, one-shot timer.  See usage notes at the top of the file.
+class OneShotTimer : public BaseTimerMethodPointer {
+ public:
+  OneShotTimer() : OneShotTimer(nullptr) {}
+  explicit OneShotTimer(TickClock* tick_clock)
+      : BaseTimerMethodPointer(ONE_SHOT, tick_clock) {}
+};
+
+//-----------------------------------------------------------------------------
+// A simple, repeating timer.  See usage notes at the top of the file.
+class RepeatingTimer : public BaseTimerMethodPointer {
+ public:
+  RepeatingTimer() : RepeatingTimer(nullptr) {}
+  explicit RepeatingTimer(TickClock* tick_clock)
+      : BaseTimerMethodPointer(REPEATING, tick_clock) {}
+};
+
+//-----------------------------------------------------------------------------
+// A Delay timer is like The Button from Lost. Once started, you have to keep
+// calling Reset otherwise it will call the given method on the sequence it was
+// initially Reset() from.
+//
+// Once created, it is inactive until Reset is called. Once |delay| seconds have
+// passed since the last call to Reset, the callback is made. Once the callback
+// has been made, it's inactive until Reset is called again.
+//
+// If destroyed, the timeout is canceled and will not occur even if already
+// inflight.
+class DelayTimer : protected Timer {
+ public:
+  template <class Receiver>
+  DelayTimer(const Location& posted_from,
+             TimeDelta delay,
+             Receiver* receiver,
+             void (Receiver::*method)())
+      : DelayTimer(posted_from, delay, receiver, method, nullptr) {}
+
+  template <class Receiver>
+  DelayTimer(const Location& posted_from,
+             TimeDelta delay,
+             Receiver* receiver,
+             void (Receiver::*method)(),
+             TickClock* tick_clock)
+      : Timer(posted_from,
+              delay,
+              base::Bind(method, base::Unretained(receiver)),
+              false,
+              tick_clock) {}
+
+  using Timer::Reset;
+};
+
+}  // namespace base
+
+#endif  // BASE_TIMER_TIMER_H_