DXR is a code search and navigation tool aimed at making sense of large projects. It supports full-text and regex searches as well as structural queries.

Header

Mercurial (5350524bb654)

VCS Links

Line Code
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271
/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#include "mozilla/TaskQueue.h"

#include "nsIEventTarget.h"
#include "nsThreadUtils.h"

namespace mozilla {

class TaskQueue::EventTargetWrapper final : public nsIEventTarget
{
  RefPtr<TaskQueue> mTaskQueue;

  ~EventTargetWrapper()
  {
  }

public:
  explicit EventTargetWrapper(TaskQueue* aTaskQueue)
    : mTaskQueue(aTaskQueue)
  {
    MOZ_ASSERT(mTaskQueue);
  }

  NS_IMETHOD
  DispatchFromScript(nsIRunnable* aEvent, uint32_t aFlags) override
  {
    nsCOMPtr<nsIRunnable> ref = aEvent;
    return Dispatch(ref.forget(), aFlags);
  }

  NS_IMETHOD
  Dispatch(already_AddRefed<nsIRunnable> aEvent, uint32_t aFlags) override
  {
    nsCOMPtr<nsIRunnable> runnable = aEvent;
    MonitorAutoLock mon(mTaskQueue->mQueueMonitor);
    return mTaskQueue->DispatchLocked(/* passed by ref */runnable,
                                      DontAssertDispatchSuccess,
                                      NormalDispatch);
  }

  NS_IMETHOD
  DelayedDispatch(already_AddRefed<nsIRunnable>, uint32_t aFlags) override
  {
    return NS_ERROR_NOT_IMPLEMENTED;
  }

  NS_IMETHOD
  IsOnCurrentThread(bool* aResult) override
  {
    *aResult = mTaskQueue->IsCurrentThreadIn();
    return NS_OK;
  }

  NS_DECL_THREADSAFE_ISUPPORTS
};

NS_IMPL_ISUPPORTS(TaskQueue::EventTargetWrapper, nsIEventTarget)

TaskQueue::TaskQueue(already_AddRefed<nsIEventTarget> aTarget,
                     bool aRequireTailDispatch)
  : AbstractThread(aRequireTailDispatch)
  , mTarget(aTarget)
  , mQueueMonitor("TaskQueue::Queue")
  , mTailDispatcher(nullptr)
  , mIsRunning(false)
  , mIsShutdown(false)
{
  MOZ_COUNT_CTOR(TaskQueue);
}

TaskQueue::~TaskQueue()
{
  MonitorAutoLock mon(mQueueMonitor);
  MOZ_ASSERT(mIsShutdown);
  MOZ_COUNT_DTOR(TaskQueue);
}

TaskDispatcher&
TaskQueue::TailDispatcher()
{
  MOZ_ASSERT(IsCurrentThreadIn());
  MOZ_ASSERT(mTailDispatcher);
  return *mTailDispatcher;
}

// Note aRunnable is passed by ref to support conditional ownership transfer.
// See Dispatch() in TaskQueue.h for more details.
nsresult
TaskQueue::DispatchLocked(nsCOMPtr<nsIRunnable>& aRunnable,
                          DispatchFailureHandling aFailureHandling,
                          DispatchReason aReason)
{
  mQueueMonitor.AssertCurrentThreadOwns();
  if (mIsShutdown) {
    return NS_ERROR_FAILURE;
  }

  AbstractThread* currentThread;
  if (aReason != TailDispatch && (currentThread = GetCurrent()) && RequiresTailDispatch(currentThread)) {
    currentThread->TailDispatcher().AddTask(this, aRunnable.forget(), aFailureHandling);
    return NS_OK;
  }

  mTasks.push(aRunnable.forget());
  if (mIsRunning) {
    return NS_OK;
  }
  RefPtr<nsIRunnable> runner(new Runner(this));
  nsresult rv = mTarget->Dispatch(runner.forget(), NS_DISPATCH_NORMAL);
  if (NS_FAILED(rv)) {
    NS_WARNING("Failed to dispatch runnable to run TaskQueue");
    return rv;
  }
  mIsRunning = true;

  return NS_OK;
}

void
TaskQueue::AwaitIdle()
{
  MonitorAutoLock mon(mQueueMonitor);
  AwaitIdleLocked();
}

void
TaskQueue::AwaitIdleLocked()
{
  // Make sure there are no tasks for this queue waiting in the caller's tail
  // dispatcher.
  MOZ_ASSERT_IF(AbstractThread::GetCurrent(),
                !AbstractThread::GetCurrent()->HasTailTasksFor(this));

  mQueueMonitor.AssertCurrentThreadOwns();
  MOZ_ASSERT(mIsRunning || mTasks.empty());
  while (mIsRunning) {
    mQueueMonitor.Wait();
  }
}

void
TaskQueue::AwaitShutdownAndIdle()
{
  MOZ_ASSERT(!IsCurrentThreadIn());
  // Make sure there are no tasks for this queue waiting in the caller's tail
  // dispatcher.
  MOZ_ASSERT_IF(AbstractThread::GetCurrent(),
                !AbstractThread::GetCurrent()->HasTailTasksFor(this));

  MonitorAutoLock mon(mQueueMonitor);
  while (!mIsShutdown) {
    mQueueMonitor.Wait();
  }
  AwaitIdleLocked();
}

RefPtr<ShutdownPromise>
TaskQueue::BeginShutdown()
{
  // Dispatch any tasks for this queue waiting in the caller's tail dispatcher,
  // since this is the last opportunity to do so.
  if (AbstractThread* currentThread = AbstractThread::GetCurrent()) {
    currentThread->TailDispatchTasksFor(this);
  }

  MonitorAutoLock mon(mQueueMonitor);
  mIsShutdown = true;
  RefPtr<ShutdownPromise> p = mShutdownPromise.Ensure(__func__);
  MaybeResolveShutdown();
  mon.NotifyAll();
  return p;
}

bool
TaskQueue::IsEmpty()
{
  MonitorAutoLock mon(mQueueMonitor);
  return mTasks.empty();
}

uint32_t
TaskQueue::ImpreciseLengthForHeuristics()
{
  MonitorAutoLock mon(mQueueMonitor);
  return mTasks.size();
}

bool
TaskQueue::IsCurrentThreadIn()
{
  bool in = NS_GetCurrentThread() == mRunningThread;
  return in;
}

already_AddRefed<nsIEventTarget>
TaskQueue::WrapAsEventTarget()
{
  nsCOMPtr<nsIEventTarget> ref = new EventTargetWrapper(this);
  return ref.forget();
}

nsresult
TaskQueue::Runner::Run()
{
  RefPtr<nsIRunnable> event;
  {
    MonitorAutoLock mon(mQueue->mQueueMonitor);
    MOZ_ASSERT(mQueue->mIsRunning);
    if (mQueue->mTasks.size() == 0) {
      mQueue->mIsRunning = false;
      mQueue->MaybeResolveShutdown();
      mon.NotifyAll();
      return NS_OK;
    }
    event = mQueue->mTasks.front().forget();
    mQueue->mTasks.pop();
  }
  MOZ_ASSERT(event);

  // Note that dropping the queue monitor before running the task, and
  // taking the monitor again after the task has run ensures we have memory
  // fences enforced. This means that if the object we're calling wasn't
  // designed to be threadsafe, it will be, provided we're only calling it
  // in this task queue.
  {
    AutoTaskGuard g(mQueue);
    event->Run();
  }

  // Drop the reference to event. The event will hold a reference to the
  // object it's calling, and we don't want to keep it alive, it may be
  // making assumptions what holds references to it. This is especially
  // the case if the object is waiting for us to shutdown, so that it
  // can shutdown (like in the MediaDecoderStateMachine's SHUTDOWN case).
  event = nullptr;

  {
    MonitorAutoLock mon(mQueue->mQueueMonitor);
    if (mQueue->mTasks.size() == 0) {
      // No more events to run. Exit the task runner.
      mQueue->mIsRunning = false;
      mQueue->MaybeResolveShutdown();
      mon.NotifyAll();
      return NS_OK;
    }
  }

  // There's at least one more event that we can run. Dispatch this Runner
  // to the target again to ensure it runs again. Note that we don't just
  // run in a loop here so that we don't hog the target. This means we may
  // run on another thread next time, but we rely on the memory fences from
  // mQueueMonitor for thread safety of non-threadsafe tasks.
  nsresult rv = mQueue->mTarget->Dispatch(this, NS_DISPATCH_AT_END);
  if (NS_FAILED(rv)) {
    // Failed to dispatch, shutdown!
    MonitorAutoLock mon(mQueue->mQueueMonitor);
    mQueue->mIsRunning = false;
    mQueue->mIsShutdown = true;
    mQueue->MaybeResolveShutdown();
    mon.NotifyAll();
  }

  return NS_OK;
}

} // namespace mozilla