src/cc/trees/blocking_task_runner.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 "cc/trees/blocking_task_runner.h"
   6
   7 #include <utility>
   8
   9 #include "base/logging.h"
  10 #include "base/memory/singleton.h"
  11 #include "base/message_loop/message_loop_proxy.h"
  12
  13 namespace cc {
  14
  15 typedef std::pair<base::SingleThreadTaskRunner*,
  16                   scoped_refptr<BlockingTaskRunner> > TaskRunnerPair;
  17
  18 struct TaskRunnerPairs {
  19   static TaskRunnerPairs* GetInstance() {
  20     return Singleton<TaskRunnerPairs>::get();
  21   }
  22
  23   base::Lock lock;
  24   std::vector<TaskRunnerPair> pairs;
  25
  26  private:
  27   friend struct DefaultSingletonTraits<TaskRunnerPairs>;
  28 };
  29
  30 // static
  31 scoped_refptr<BlockingTaskRunner> BlockingTaskRunner::current() {
  32   TaskRunnerPairs* task_runners = TaskRunnerPairs::GetInstance();
  33
  34   base::AutoLock lock(task_runners->lock);
  35
  36   for (size_t i = 0; i < task_runners->pairs.size(); ++i) {
  37     if (task_runners->pairs[i].first->HasOneRef()) {
  38       // The SingleThreadTaskRunner is kept alive by its MessageLoop, and we
  39       // hold a second reference in the TaskRunnerPairs array. If the
  40       // SingleThreadTaskRunner has one ref, then it is being held alive only
  41       // by the BlockingTaskRunner and the MessageLoop is gone, so drop the
  42       // BlockingTaskRunner from the TaskRunnerPairs array along with the
  43       // SingleThreadTaskRunner.
  44       task_runners->pairs.erase(task_runners->pairs.begin() + i);
  45       --i;
  46     }
  47   }
  48
  49   scoped_refptr<base::SingleThreadTaskRunner> current =
  50       base::MessageLoopProxy::current();
  51   for (size_t i = 0; i < task_runners->pairs.size(); ++i) {
  52     if (task_runners->pairs[i].first == current.get())
  53       return task_runners->pairs[i].second.get();
  54   }
  55
  56   scoped_refptr<BlockingTaskRunner> runner = new BlockingTaskRunner(current);
  57   task_runners->pairs.push_back(TaskRunnerPair(current, runner));
  58   return runner;
  59 }
  60
  61 BlockingTaskRunner::BlockingTaskRunner(
  62     scoped_refptr<base::SingleThreadTaskRunner> task_runner)
  63     : task_runner_(task_runner), capture_(0) {}
  64
  65 BlockingTaskRunner::~BlockingTaskRunner() {}
  66
  67 bool BlockingTaskRunner::PostTask(const tracked_objects::Location& from_here,
  68                                   const base::Closure& task) {
  69   base::AutoLock lock(lock_);
  70   if (!capture_)
  71     return task_runner_->PostTask(from_here, task);
  72   captured_tasks_.push_back(task);
  73   return true;
  74 }
  75
  76 void BlockingTaskRunner::SetCapture(bool capture) {
  77   DCHECK(BelongsToCurrentThread());
  78
  79   std::vector<base::Closure> tasks;
  80
  81   {
  82     base::AutoLock lock(lock_);
  83     capture_ += capture ? 1 : -1;
  84     DCHECK_GE(capture_, 0);
  85
  86     if (capture_)
  87       return;
  88
  89     // We're done capturing, so grab all the captured tasks and run them.
  90     tasks.swap(captured_tasks_);
  91   }
  92   for (size_t i = 0; i < tasks.size(); ++i)
  93     tasks[i].Run();
  94 }
  95
  96 BlockingTaskRunner::CapturePostTasks::CapturePostTasks()
  97     : blocking_runner_(BlockingTaskRunner::current()) {
  98   blocking_runner_->SetCapture(true);
  99 }
 100
 101 BlockingTaskRunner::CapturePostTasks::~CapturePostTasks() {
 102   blocking_runner_->SetCapture(false);
 103 }
 104
 105 }  // namespace cc