base/one_shot_event.cc

   1 // Copyright 2013 The Chromium Authors
   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/functional/callback.h"
  11 #include "base/location.h"
  12 #include "base/task/single_thread_task_runner.h"
  13 #include "base/task/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),
  59            SingleThreadTaskRunner::GetCurrentDefault(), delay);
  60 }
  61
  62 void OneShotEvent::Signal() {
  63   DCHECK(thread_checker_.CalledOnValidThread());
  64
  65   CHECK(!signaled_) << "Only call Signal once.";
  66
  67   signaled_ = true;
  68   // After this point, a call to Post() from one of the queued tasks
  69   // could proceed immediately, but the fact that this object is
  70   // single-threaded prevents that from being relevant.
  71
  72   // Move tasks to a temporary to ensure no new ones are added.
  73   std::vector<TaskInfo> moved_tasks;
  74   std::swap(moved_tasks, tasks_);
  75
  76   // We could randomize tasks in debug mode in order to check that
  77   // the order doesn't matter...
  78   for (TaskInfo& task : moved_tasks) {
  79     if (task.delay.is_zero())
  80       task.runner->PostTask(task.from_here, std::move(task.task));
  81     else
  82       task.runner->PostDelayedTask(task.from_here, std::move(task.task),
  83                                    task.delay);
  84   }
  85   DCHECK(tasks_.empty()) << "No new tasks should be added during task running!";
  86 }
  87
  88 void OneShotEvent::PostImpl(const Location& from_here,
  89                             OnceClosure task,
  90                             scoped_refptr<SingleThreadTaskRunner> runner,
  91                             const TimeDelta& delay) const {
  92   DCHECK(thread_checker_.CalledOnValidThread());
  93
  94   if (is_signaled()) {
  95     if (delay.is_zero())
  96       runner->PostTask(from_here, std::move(task));
  97     else
  98       runner->PostDelayedTask(from_here, std::move(task), delay);
  99   } else {
 100     tasks_.emplace_back(from_here, std::move(runner), std::move(task), delay);
 101   }
 102 }
 103
 104 }  // namespace base