base/timer/timer.cc

   1 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #include "base/timer/timer.h"
   6
   7 #include <stddef.h>
   8
   9 #include "base/logging.h"
  10 #include "base/memory/ref_counted.h"
  11 #include "base/single_thread_task_runner.h"
  12 #include "base/thread_task_runner_handle.h"
  13 #include "base/threading/platform_thread.h"
  14
  15 namespace base {
  16
  17 // BaseTimerTaskInternal is a simple delegate for scheduling a callback to
  18 // Timer in the thread's default task runner. It also handles the following
  19 // edge cases:
  20 // - deleted by the task runner.
  21 // - abandoned (orphaned) by Timer.
  22 class BaseTimerTaskInternal {
  23  public:
  24   explicit BaseTimerTaskInternal(Timer* timer)
  25       : timer_(timer) {
  26   }
  27
  28   ~BaseTimerTaskInternal() {
  29     // This task may be getting cleared because the task runner has been
  30     // destructed.  If so, don't leave Timer with a dangling pointer
  31     // to this.
  32     if (timer_)
  33       timer_->StopAndAbandon();
  34   }
  35
  36   void Run() {
  37     // timer_ is NULL if we were abandoned.
  38     if (!timer_)
  39       return;
  40
  41     // *this will be deleted by the task runner, so Timer needs to
  42     // forget us:
  43     timer_->scheduled_task_ = NULL;
  44
  45     // Although Timer should not call back into *this, let's clear
  46     // the timer_ member first to be pedantic.
  47     Timer* timer = timer_;
  48     timer_ = NULL;
  49     timer->RunScheduledTask();
  50   }
  51
  52   // The task remains in the MessageLoop queue, but nothing will happen when it
  53   // runs.
  54   void Abandon() {
  55     timer_ = NULL;
  56   }
  57
  58  private:
  59   Timer* timer_;
  60 };
  61
  62 Timer::Timer(bool retain_user_task, bool is_repeating)
  63     : scheduled_task_(NULL),
  64       thread_id_(0),
  65       is_repeating_(is_repeating),
  66       retain_user_task_(retain_user_task),
  67       is_running_(false) {
  68 }
  69
  70 Timer::Timer(const tracked_objects::Location& posted_from,
  71              TimeDelta delay,
  72              const base::Closure& user_task,
  73              bool is_repeating)
  74     : scheduled_task_(NULL),
  75       posted_from_(posted_from),
  76       delay_(delay),
  77       user_task_(user_task),
  78       thread_id_(0),
  79       is_repeating_(is_repeating),
  80       retain_user_task_(true),
  81       is_running_(false) {
  82 }
  83
  84 Timer::~Timer() {
  85   StopAndAbandon();
  86 }
  87
  88 bool Timer::IsRunning() const {
  89   return is_running_;
  90 }
  91
  92 TimeDelta Timer::GetCurrentDelay() const {
  93   return delay_;
  94 }
  95
  96 void Timer::Start(const tracked_objects::Location& posted_from,
  97                   TimeDelta delay,
  98                   const base::Closure& user_task) {
  99   SetTaskInfo(posted_from, delay, user_task);
 100   Reset();
 101 }
 102
 103 void Timer::Stop() {
 104   is_running_ = false;
 105   if (!retain_user_task_)
 106     user_task_.Reset();
 107 }
 108
 109 void Timer::Reset() {
 110   DCHECK(!user_task_.is_null());
 111
 112   // If there's no pending task, start one up and return.
 113   if (!scheduled_task_) {
 114     PostNewScheduledTask(delay_);
 115     return;
 116   }
 117
 118   // Set the new desired_run_time_.
 119   if (delay_ > TimeDelta::FromMicroseconds(0))
 120     desired_run_time_ = TimeTicks::Now() + delay_;
 121   else
 122     desired_run_time_ = TimeTicks();
 123
 124   // We can use the existing scheduled task if it arrives before the new
 125   // desired_run_time_.
 126   if (desired_run_time_ >= scheduled_run_time_) {
 127     is_running_ = true;
 128     return;
 129   }
 130
 131   // We can't reuse the scheduled_task_, so abandon it and post a new one.
 132   AbandonScheduledTask();
 133   PostNewScheduledTask(delay_);
 134 }
 135
 136 void Timer::SetTaskInfo(const tracked_objects::Location& posted_from,
 137                         TimeDelta delay,
 138                         const base::Closure& user_task) {
 139   posted_from_ = posted_from;
 140   delay_ = delay;
 141   user_task_ = user_task;
 142 }
 143
 144 void Timer::PostNewScheduledTask(TimeDelta delay) {
 145   DCHECK(scheduled_task_ == NULL);
 146   is_running_ = true;
 147   scheduled_task_ = new BaseTimerTaskInternal(this);
 148   if (delay > TimeDelta::FromMicroseconds(0)) {
 149     ThreadTaskRunnerHandle::Get()->PostDelayedTask(posted_from_,
 150         base::Bind(&BaseTimerTaskInternal::Run, base::Owned(scheduled_task_)),
 151         delay);
 152     scheduled_run_time_ = desired_run_time_ = TimeTicks::Now() + delay;
 153   } else {
 154     ThreadTaskRunnerHandle::Get()->PostTask(posted_from_,
 155         base::Bind(&BaseTimerTaskInternal::Run, base::Owned(scheduled_task_)));
 156     scheduled_run_time_ = desired_run_time_ = TimeTicks();
 157   }
 158   // Remember the thread ID that posts the first task -- this will be verified
 159   // later when the task is abandoned to detect misuse from multiple threads.
 160   if (!thread_id_)
 161     thread_id_ = static_cast<int>(PlatformThread::CurrentId());
 162 }
 163
 164 void Timer::AbandonScheduledTask() {
 165   DCHECK(thread_id_ == 0 ||
 166          thread_id_ == static_cast<int>(PlatformThread::CurrentId()));
 167   if (scheduled_task_) {
 168     scheduled_task_->Abandon();
 169     scheduled_task_ = NULL;
 170   }
 171 }
 172
 173 void Timer::RunScheduledTask() {
 174   // Task may have been disabled.
 175   if (!is_running_)
 176     return;
 177
 178   // First check if we need to delay the task because of a new target time.
 179   if (desired_run_time_ > scheduled_run_time_) {
 180     // TimeTicks::Now() can be expensive, so only call it if we know the user
 181     // has changed the desired_run_time_.
 182     TimeTicks now = TimeTicks::Now();
 183     // Task runner may have called us late anyway, so only post a continuation
 184     // task if the desired_run_time_ is in the future.
 185     if (desired_run_time_ > now) {
 186       // Post a new task to span the remaining time.
 187       PostNewScheduledTask(desired_run_time_ - now);
 188       return;
 189     }
 190   }
 191
 192   // Make a local copy of the task to run. The Stop method will reset the
 193   // user_task_ member if retain_user_task_ is false.
 194   base::Closure task = user_task_;
 195
 196   if (is_repeating_)
 197     PostNewScheduledTask(delay_);
 198   else
 199     Stop();
 200
 201   task.Run();
 202
 203   // No more member accesses here: *this could be deleted at this point.
 204 }
 205
 206 }  // namespace base