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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<MyClass> 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.
// NOTE: These APIs are not thread safe. Always call from the same thread.
// IMPORTANT: If you change timer code, make sure that all tests (including
// disabled ones) from 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/basictypes.h"
#include "base/bind.h"
#include "base/bind_helpers.h"
#include "base/callback.h"
#include "base/location.h"
#include "base/time/time.h"
namespace base {
class BaseTimerTaskInternal;
// This class wraps MessageLoop::PostDelayedTask to manage delayed and repeating
// tasks. It must be destructed on the same thread that starts tasks. There are
// DCHECKs in place to verify this.
class BASE_EXPORT Timer {
// Construct a timer in repeating or one-shot mode. Start or SetTaskInfo 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.
Timer(bool retain_user_task, bool is_repeating);
// Construct a timer with retained task info.
Timer(const tracked_objects::Location& posted_from,
TimeDelta delay,
const base::Closure& user_task,
bool is_repeating);
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;
// 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 tracked_objects::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();
// 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_; }
// Used to initiate a new delayed task. This has the side-effect of disabling
// scheduled_task_ if it is non-null.
void SetTaskInfo(const tracked_objects::Location& posted_from,
TimeDelta delay,
const base::Closure& user_task);
bool retain_user_task() const { return retain_user_task_; }
bool is_repeating() const { return is_repeating_; }
friend class BaseTimerTaskInternal;
// Allocates a new scheduled_task_ and posts it on the current MessageLoop
// 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);
// Disable scheduled_task_ and abandon it so that it no longer refers back to
// this object.
void AbandonScheduledTask();
// Called by BaseTimerTaskInternal when the MessageLoop runs it.
void RunScheduledTask();
// Stop running task (if any) and abandon scheduled task (if any).
void StopAndAbandon() {
// When non-NULL, the scheduled_task_ is waiting in the MessageLoop to call
// RunScheduledTask() at scheduled_run_time_.
BaseTimerTaskInternal* scheduled_task_;
// Location in user code.
tracked_objects::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 estimated time that the MessageLoop will run the scheduled_task_ that
// will call RunScheduledTask(). 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 MessageLoop 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_;
// Thread ID of current MessageLoop for verifying single-threaded usage.
int thread_id_;
// 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_;
// If true, user_task_ is scheduled to run sometime in the future.
bool is_running_;
// This class is an implementation detail of OneShotTimer and RepeatingTimer.
// Please do not use this class directly.
template <class Receiver, bool kIsRepeating>
class BaseTimerMethodPointer : public Timer {
typedef void (Receiver::*ReceiverMethod)();
// 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;
BaseTimerMethodPointer() : Timer(kIsRepeating, kIsRepeating) {}
// 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|.
virtual void Start(const tracked_objects::Location& posted_from,
TimeDelta delay,
Receiver* receiver,
ReceiverMethod 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.
template <class Receiver>
class OneShotTimer : public BaseTimerMethodPointer<Receiver, false> {};
// A simple, repeating timer. See usage notes at the top of the file.
template <class Receiver>
class RepeatingTimer : public BaseTimerMethodPointer<Receiver, true> {};
// A Delay timer is like The Button from Lost. Once started, you have to keep
// calling Reset otherwise it will call the given method in the MessageLoop
// thread.
// 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.
template <class Receiver>
class DelayTimer : protected Timer {
typedef void (Receiver::*ReceiverMethod)();
DelayTimer(const tracked_objects::Location& posted_from,
TimeDelta delay,
Receiver* receiver,
ReceiverMethod method)
: Timer(posted_from, delay,
base::Bind(method, base::Unretained(receiver)),
false) {}
void Reset() { Timer::Reset(); }
} // namespace base