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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, RepeatingTimer and RetainingOneShotTimer 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.
// RetainingOneShotTimer doesn't repeat the task itself like RepeatingTimer, but
// retains the given task after the time out. You can restart it with Reset
// again without giving new task to Start.
//
// All of OneShotTimer, RepeatingTimer and RetainingOneShotTimer 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
// timer 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_;
// };
//
// Timers 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. When a method is called (except the
// constructor), all further method calls must be on the same sequence until
// Stop().
//
// By default, the scheduled tasks will be run on the same sequence that the
// Timer was *started on*. To mock time in unit tests, some old tests used
// SetTaskRunner() to schedule the delay on a test-controlled TaskRunner. The
// modern and preferred approach to mock time is to use TaskEnvironment's
// MOCK_TIME mode.
#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 "base/base_export.h"
#include "base/bind.h"
#include "base/callback.h"
#include "base/callback_helpers.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 TickClock;
namespace internal {
class TaskDestructionDetector;
//-----------------------------------------------------------------------------
// This class wraps TaskRunner::PostDelayedTask to manage delayed and repeating
// tasks. See meta comment above for thread-safety requirements.
// Do not use this class directly. Use one of OneShotTimer, RepeatingTimer or
// RetainingOneShotTimer.
//
class BASE_EXPORT TimerBase {
public:
// Constructs a timer. Start must be called later to set task info.
// If |tick_clock| is provided, it is used instead of TimeTicks::Now() to get
// TimeTicks when scheduling tasks.
TimerBase();
explicit TimerBase(const TickClock* tick_clock);
// Construct a timer with task info.
// If |tick_clock| is provided, it is used instead of TimeTicks::Now() to get
// TimeTicks when scheduling tasks.
TimerBase(const Location& posted_from, TimeDelta delay);
TimerBase(const Location& posted_from,
TimeDelta delay,
const TickClock* tick_clock);
virtual ~TimerBase();
// Returns true if the timer is running (i.e., not stopped).
bool IsRunning() const;
// Returns the current delay for this timer.
TimeDelta GetCurrentDelay() const;
// Sets the task runner on which the delayed task should be scheduled when
// this Timer is running. This method can only be called while this Timer
// isn't running. This is an alternative (old) approach to mock time in tests.
// The modern and preferred approach is to use
// TaskEnvironment::TimeSource::MOCK_TIME. To avoid racy usage of Timer,
// |task_runner| must run tasks on the same sequence which this Timer is bound
// to (started from). TODO(gab): Migrate all callers to
// TaskEnvironment::TimeSource::MOCK_TIME.
virtual void SetTaskRunner(scoped_refptr<SequencedTaskRunner> task_runner);
// Call this method to stop and cancel the timer. It is a no-op if the timer
// is not running.
virtual void Stop();
// Abandons the scheduled task (if any) and stops the timer (if running).
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 TimeTicks& desired_run_time() const { return desired_run_time_; }
protected:
virtual void OnStop() = 0;
virtual void RunUserTask() = 0;
// 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_;
// 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_;
// Schedules |OnScheduledTaskInvoked()| to run on the current sequence with
// the given |delay|. |scheduled_run_time_| and |desired_run_time_| are reset
// to Now() + delay.
void ScheduleNewTask(TimeDelta delay);
void StartInternal(const Location& posted_from, TimeDelta delay);
private:
friend class BaseTimerTaskInternal;
// 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();
// Returns the current tick count.
TimeTicks Now() const;
// Disables the scheduled task and abandon it so that it no longer refers back
// to this object.
void AbandonScheduledTask();
// Called when the scheduled task is invoked. Will run the |user_task| if the
// timer is still running and |desired_run_time_| was reached.
// |task_destruction_detector| is owned by the callback to detect when the
// scheduled task is deleted before being executed.
void OnScheduledTaskInvoked(
std::unique_ptr<TaskDestructionDetector> task_destruction_detector);
// Detects when the scheduled task is deleted before being executed. Null when
// there is no scheduled task.
TaskDestructionDetector* task_destruction_detector_;
// Location in user code.
Location posted_from_;
// Delay requested by user.
TimeDelta delay_;
// The time at which the scheduled task is expected to fire. This time can be
// null 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_;
// The tick clock used to calculate the run time for scheduled tasks.
const TickClock* const tick_clock_;
// If true, |user_task_| is scheduled to run sometime in the future.
bool is_running_;
WeakPtrFactory<TimerBase> weak_ptr_factory_{this};
DISALLOW_COPY_AND_ASSIGN(TimerBase);
};
} // namespace internal
//-----------------------------------------------------------------------------
// A simple, one-shot timer. See usage notes at the top of the file.
class BASE_EXPORT OneShotTimer : public internal::TimerBase {
public:
OneShotTimer();
explicit OneShotTimer(const TickClock* tick_clock);
~OneShotTimer() override;
// 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,
OnceClosure user_task);
// 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
// |receiver->*method|.
template <class Receiver>
void Start(const Location& posted_from,
TimeDelta delay,
Receiver* receiver,
void (Receiver::*method)()) {
Start(posted_from, delay, BindOnce(method, Unretained(receiver)));
}
// Run the scheduled task immediately, and stop the timer. The timer needs to
// be running.
void FireNow();
private:
void OnStop() final;
void RunUserTask() final;
OnceClosure user_task_;
DISALLOW_COPY_AND_ASSIGN(OneShotTimer);
};
//-----------------------------------------------------------------------------
// A simple, repeating timer. See usage notes at the top of the file.
class BASE_EXPORT RepeatingTimer : public internal::TimerBase {
public:
RepeatingTimer();
explicit RepeatingTimer(const TickClock* tick_clock);
~RepeatingTimer() override;
RepeatingTimer(const Location& posted_from,
TimeDelta delay,
RepeatingClosure user_task);
RepeatingTimer(const Location& posted_from,
TimeDelta delay,
RepeatingClosure user_task,
const TickClock* 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 the given |user_task|.
virtual void Start(const Location& posted_from,
TimeDelta delay,
RepeatingClosure user_task);
// 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
// |receiver->*method|.
template <class Receiver>
void Start(const Location& posted_from,
TimeDelta delay,
Receiver* receiver,
void (Receiver::*method)()) {
Start(posted_from, delay, BindRepeating(method, Unretained(receiver)));
}
const RepeatingClosure& user_task() const { return user_task_; }
private:
// Mark this final, so that the destructor can call this safely.
void OnStop() final;
void RunUserTask() override;
RepeatingClosure user_task_;
DISALLOW_COPY_AND_ASSIGN(RepeatingTimer);
};
//-----------------------------------------------------------------------------
// A simple, one-shot timer with the retained user_task which is reused for
// multiple invocations of Start(). See usage notes at the top of the file.
class BASE_EXPORT RetainingOneShotTimer : public internal::TimerBase {
public:
RetainingOneShotTimer();
explicit RetainingOneShotTimer(const TickClock* tick_clock);
~RetainingOneShotTimer() override;
RetainingOneShotTimer(const Location& posted_from,
TimeDelta delay,
RepeatingClosure user_task);
RetainingOneShotTimer(const Location& posted_from,
TimeDelta delay,
RepeatingClosure user_task,
const TickClock* 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 the given |user_task|.
virtual void Start(const Location& posted_from,
TimeDelta delay,
RepeatingClosure user_task);
// 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
// |receiver->*method|.
template <class Receiver>
void Start(const Location& posted_from,
TimeDelta delay,
Receiver* receiver,
void (Receiver::*method)()) {
Start(posted_from, delay, BindRepeating(method, Unretained(receiver)));
}
const RepeatingClosure& user_task() const { return user_task_; }
private:
// Mark this final, so that the destructor can call this safely.
void OnStop() final;
void RunUserTask() override;
RepeatingClosure user_task_;
DISALLOW_COPY_AND_ASSIGN(RetainingOneShotTimer);
};
//-----------------------------------------------------------------------------
// 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 {
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)(),
const TickClock* tick_clock)
: timer_(posted_from,
delay,
BindRepeating(method, Unretained(receiver)),
tick_clock) {}
void Reset() { timer_.Reset(); }
private:
RetainingOneShotTimer timer_;
DISALLOW_COPY_AND_ASSIGN(DelayTimer);
};
} // namespace base
#endif // BASE_TIMER_TIMER_H_