base/one_shot_event.cc

   1 // Copyright 2013 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/one_shot_event.h"
   6
   7 #include <stddef.h>
   8 #include <utility>
   9
  10 #include "base/callback.h"
  11 #include "base/location.h"
  12 #include "base/single_thread_task_runner.h"
  13 #include "base/task_runner.h"
  14 #include "base/time/time.h"
  15
  16 namespace base {
  17
  18 struct OneShotEvent::TaskInfo {
  19   TaskInfo() {}
  20   TaskInfo(const Location& from_here,
  21            scoped_refptr<SingleThreadTaskRunner> runner,
  22            OnceClosure task,
  23            const TimeDelta& delay)
  24       : from_here(from_here),
  25         runner(std::move(runner)),
  26         task(std::move(task)),
  27         delay(delay) {
  28     CHECK(this->runner.get());  // Detect mistakes with a decent stack frame.
  29   }
  30   TaskInfo(TaskInfo&&) = default;
  31   TaskInfo& operator=(TaskInfo&&) = default;
  32
  33   Location from_here;
  34   scoped_refptr<SingleThreadTaskRunner> runner;
  35   OnceClosure task;
  36   TimeDelta delay;
  37 };
  38
  39 OneShotEvent::OneShotEvent() : signaled_(false) {
  40   // It's acceptable to construct the OneShotEvent on one thread, but
  41   // immediately move it to another thread.
  42   thread_checker_.DetachFromThread();
  43 }
  44 OneShotEvent::OneShotEvent(bool signaled) : signaled_(signaled) {
  45   thread_checker_.DetachFromThread();
  46 }
  47 OneShotEvent::~OneShotEvent() {}
  48
  49 void OneShotEvent::Post(const Location& from_here,
  50                         OnceClosure task,
  51                         scoped_refptr<SingleThreadTaskRunner> runner) const {
  52   PostImpl(from_here, std::move(task), std::move(runner), TimeDelta());
  53 }
  54
  55 void OneShotEvent::PostDelayed(const Location& from_here,
  56                                OnceClosure task,
  57                                const TimeDelta& delay) const {
  58   PostImpl(from_here, std::move(task), ThreadTaskRunnerHandle::Get(), delay);
  59 }
  60
  61 void OneShotEvent::Signal() {
  62   DCHECK(thread_checker_.CalledOnValidThread());
  63
  64   CHECK(!signaled_) << "Only call Signal once.";
  65
  66   signaled_ = true;
  67   // After this point, a call to Post() from one of the queued tasks
  68   // could proceed immediately, but the fact that this object is
  69   // single-threaded prevents that from being relevant.
  70
  71   // Move tasks to a temporary to ensure no new ones are added.
  72   std::vector<TaskInfo> moved_tasks;
  73   std::swap(moved_tasks, tasks_);
  74
  75   // We could randomize tasks in debug mode in order to check that
  76   // the order doesn't matter...
  77   for (TaskInfo& task : moved_tasks) {
  78     if (task.delay.is_zero())
  79       task.runner->PostTask(task.from_here, std::move(task.task));
  80     else
  81       task.runner->PostDelayedTask(task.from_here, std::move(task.task),
  82                                    task.delay);
  83   }
  84   DCHECK(tasks_.empty()) << "No new tasks should be added during task running!";
  85 }
  86
  87 void OneShotEvent::PostImpl(const Location& from_here,
  88                             OnceClosure task,
  89                             scoped_refptr<SingleThreadTaskRunner> runner,
  90                             const TimeDelta& delay) const {
  91   DCHECK(thread_checker_.CalledOnValidThread());
  92
  93   if (is_signaled()) {
  94     if (delay.is_zero())
  95       runner->PostTask(from_here, std::move(task));
  96     else
  97       runner->PostDelayedTask(from_here, std::move(task), delay);
  98   } else {
  99     tasks_.emplace_back(from_here, std::move(runner), std::move(task), delay);
 100   }
 101 }
 102
 103 }  // namespace base