1 files changed, 271 insertions, 0 deletions
diff --git a/xpcom/threads/TaskQueue.cpp b/xpcom/threads/TaskQueue.cpp
new file mode 100644
index 000000000..2e593a773
--- /dev/null
+++ b/xpcom/threads/TaskQueue.cpp
@@ -0,0 +1,271 @@
+/* -*- 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