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Bug 1151656 - Implement TaskDispatcher.h. r=mattwoodrow
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147
dom/media/TaskDispatcher.h
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147
dom/media/TaskDispatcher.h
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/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
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/* vim:set ts=2 sw=2 sts=2 et cindent: */
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/* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
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#if !defined(TaskDispatcher_h_)
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#define TaskDispatcher_h_
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#include "AbstractThread.h"
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#include "mozilla/UniquePtr.h"
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#include "mozilla/unused.h"
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#include "nsISupportsImpl.h"
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#include "nsTArray.h"
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#include "nsThreadUtils.h"
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namespace mozilla {
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/*
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* A classic approach to cross-thread communication is to dispatch asynchronous
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* runnables to perform updates on other threads. This generally works well, but
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* there are sometimes reasons why we might want to delay the actual dispatch of
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* these tasks until a specified moment. At present, this is primarily useful to
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* ensure that mirrored state gets updated atomically - but there may be other
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* applications as well.
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*
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* TaskDispatcher is a general abstract class that accepts tasks and dispatches
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* them at some later point. These groups of tasks are per-target-thread, and
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* contain separate queues for two kinds of tasks - "state change tasks" (which
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* run first, and are intended to be used to update the value held by mirrors),
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* and regular tasks, which are other arbitrary operations that the are gated
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* to run after all the state changes have completed.
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*/
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class TaskDispatcher
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{
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public:
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TaskDispatcher() {}
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virtual ~TaskDispatcher() {}
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virtual void AddStateChangeTask(AbstractThread* aThread,
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already_AddRefed<nsIRunnable> aRunnable) = 0;
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virtual void AddTask(AbstractThread* aThread,
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already_AddRefed<nsIRunnable> aRunnable,
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bool aAssertDispatchSuccess = true) = 0;
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};
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/*
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* AutoTaskDispatcher is a stack-scoped TaskDispatcher implementation that fires
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* its queued tasks when it is popped off the stack.
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*/
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class MOZ_STACK_CLASS AutoTaskDispatcher : public TaskDispatcher
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{
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public:
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AutoTaskDispatcher() {}
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~AutoTaskDispatcher()
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{
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for (size_t i = 0; i < mTaskGroups.Length(); ++i) {
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UniquePtr<PerThreadTaskGroup> group(Move(mTaskGroups[i]));
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nsRefPtr<AbstractThread> thread = group->mThread;
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bool assertDispatchSuccess = group->mAssertDispatchSuccess;
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nsCOMPtr<nsIRunnable> r = new TaskGroupRunnable(Move(group));
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nsresult rv = thread->Dispatch(r.forget());
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MOZ_DIAGNOSTIC_ASSERT(!assertDispatchSuccess || NS_SUCCEEDED(rv));
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unused << rv;
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}
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}
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void AddStateChangeTask(AbstractThread* aThread,
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already_AddRefed<nsIRunnable> aRunnable) override
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{
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EnsureTaskGroup(aThread).mStateChangeTasks.AppendElement(aRunnable);
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}
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void AddTask(AbstractThread* aThread,
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already_AddRefed<nsIRunnable> aRunnable,
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bool aAssertDispatchSuccess) override
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{
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PerThreadTaskGroup& group = EnsureTaskGroup(aThread);
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group.mRegularTasks.AppendElement(aRunnable);
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// The task group needs to assert dispatch success if any of the runnables
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// it's dispatching want to assert it.
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group.mAssertDispatchSuccess = group.mAssertDispatchSuccess || aAssertDispatchSuccess;
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}
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private:
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struct PerThreadTaskGroup
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{
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public:
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explicit PerThreadTaskGroup(AbstractThread* aThread)
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: mThread(aThread), mAssertDispatchSuccess(false)
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{
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MOZ_COUNT_CTOR(PerThreadTaskGroup);
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}
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~PerThreadTaskGroup() { MOZ_COUNT_DTOR(PerThreadTaskGroup); }
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nsRefPtr<AbstractThread> mThread;
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nsTArray<nsCOMPtr<nsIRunnable>> mStateChangeTasks;
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nsTArray<nsCOMPtr<nsIRunnable>> mRegularTasks;
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bool mAssertDispatchSuccess;
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};
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class TaskGroupRunnable : public nsRunnable
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{
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public:
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explicit TaskGroupRunnable(UniquePtr<PerThreadTaskGroup>&& aTasks) : mTasks(Move(aTasks)) {}
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NS_IMETHODIMP Run()
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{
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for (size_t i = 0; i < mTasks->mStateChangeTasks.Length(); ++i) {
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mTasks->mStateChangeTasks[i]->Run();
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}
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for (size_t i = 0; i < mTasks->mRegularTasks.Length(); ++i) {
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mTasks->mRegularTasks[i]->Run();
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}
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return NS_OK;
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}
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private:
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UniquePtr<PerThreadTaskGroup> mTasks;
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};
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PerThreadTaskGroup& EnsureTaskGroup(AbstractThread* aThread)
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{
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for (size_t i = 0; i < mTaskGroups.Length(); ++i) {
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if (mTaskGroups[i]->mThread == aThread) {
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return *mTaskGroups[i];
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}
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}
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mTaskGroups.AppendElement(new PerThreadTaskGroup(aThread));
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return *mTaskGroups.LastElement();
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}
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// Task groups, organized by thread.
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nsTArray<UniquePtr<PerThreadTaskGroup>> mTaskGroups;
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};
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} // namespace mozilla
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#endif
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@ -122,6 +122,7 @@ EXPORTS += [
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'SharedBuffer.h',
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'SharedThreadPool.h',
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'StreamBuffer.h',
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'TaskDispatcher.h',
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'ThreadPoolCOMListener.h',
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'TimeUnits.h',
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'TimeVarying.h',
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