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/* -*- 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
#include "mozilla/TaskQueue.h"
#include "mozilla/ProfilerRunnable.h"
#include "nsIEventTarget.h"
#include "nsITargetShutdownTask.h"
#include "nsThreadUtils.h"
#include "nsQueryObject.h"
namespace mozilla {
// Handle for a TaskQueue being tracked by a TaskQueueTracker. When created,
// it is registered with the TaskQueueTracker, and when destroyed it is
// unregistered. Holds a threadsafe weak reference to the TaskQueue.
class TaskQueueTrackerEntry final
: private LinkedListElement<TaskQueueTrackerEntry> {
public:
TaskQueueTrackerEntry(TaskQueueTracker* aTracker,
const RefPtr<TaskQueue>& aQueue)
: mTracker(aTracker), mQueue(aQueue) {
MutexAutoLock lock(mTracker->mMutex);
mTracker->mEntries.insertFront(this);
}
~TaskQueueTrackerEntry() {
MutexAutoLock lock(mTracker->mMutex);
removeFrom(mTracker->mEntries);
}
TaskQueueTrackerEntry(const TaskQueueTrackerEntry&) = delete;
TaskQueueTrackerEntry(TaskQueueTrackerEntry&&) = delete;
TaskQueueTrackerEntry& operator=(const TaskQueueTrackerEntry&) = delete;
TaskQueueTrackerEntry& operator=(TaskQueueTrackerEntry&&) = delete;
RefPtr<TaskQueue> GetQueue() const { return RefPtr<TaskQueue>(mQueue); }
private:
friend class LinkedList<TaskQueueTrackerEntry>;
friend class LinkedListElement<TaskQueueTrackerEntry>;
const RefPtr<TaskQueueTracker> mTracker;
const ThreadSafeWeakPtr<TaskQueue> mQueue;
};
RefPtr<TaskQueue> TaskQueue::Create(already_AddRefed<nsIEventTarget> aTarget,
const char* aName,
bool aSupportsTailDispatch) {
nsCOMPtr<nsIEventTarget> target(std::move(aTarget));
RefPtr<TaskQueue> queue =
new TaskQueue(do_AddRef(target), aName, aSupportsTailDispatch);
// If |target| is a TaskQueueTracker, register this TaskQueue with it. It will
// be unregistered when the TaskQueue is destroyed or shut down.
if (RefPtr<TaskQueueTracker> tracker = do_QueryObject(target)) {
MonitorAutoLock lock(queue->mQueueMonitor);
queue->mTrackerEntry = MakeUnique<TaskQueueTrackerEntry>(tracker, queue);
}
return queue;
}
TaskQueue::TaskQueue(already_AddRefed<nsIEventTarget> aTarget,
const char* aName, bool aSupportsTailDispatch)
: AbstractThread(aSupportsTailDispatch),
mTarget(aTarget),
mQueueMonitor("TaskQueue::Queue"),
mTailDispatcher(nullptr),
mIsRunning(false),
mIsShutdown(false),
mName(aName) {}
TaskQueue::~TaskQueue() {
// We should never free the TaskQueue if it was destroyed abnormally, meaning
// that all cleanup tasks should be complete if we do.
MOZ_ASSERT(mShutdownTasks.IsEmpty());
}
NS_IMPL_ADDREF_INHERITED(TaskQueue, SupportsThreadSafeWeakPtr<TaskQueue>)
NS_IMPL_RELEASE_INHERITED(TaskQueue, SupportsThreadSafeWeakPtr<TaskQueue>)
NS_IMPL_QUERY_INTERFACE(TaskQueue, nsIDirectTaskDispatcher,
nsISerialEventTarget, nsIEventTarget)
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,
uint32_t aFlags, DispatchReason aReason) {
mQueueMonitor.AssertCurrentThreadOwns();
// Continue to allow dispatches after shutdown until the last message has been
// processed, at which point no more messages will be accepted.
if (mIsShutdown && !mIsRunning) {
return NS_ERROR_UNEXPECTED;
}
AbstractThread* currentThread;
if (aReason != TailDispatch && (currentThread = GetCurrent()) &&
RequiresTailDispatch(currentThread) &&
currentThread->IsTailDispatcherAvailable()) {
MOZ_ASSERT(aFlags == NS_DISPATCH_NORMAL,
"Tail dispatch doesn't support flags");
return currentThread->TailDispatcher().AddTask(this, aRunnable.forget());
}
LogRunnable::LogDispatch(aRunnable);
mTasks.Push({std::move(aRunnable), aFlags});
if (mIsRunning) {
return NS_OK;
}
RefPtr<nsIRunnable> runner(new Runner(this));
nsresult rv = mTarget->Dispatch(runner.forget(), aFlags);
if (NS_FAILED(rv)) {
NS_WARNING("Failed to dispatch runnable to run TaskQueue");
return rv;
}
mIsRunning = true;
return NS_OK;
}
nsresult TaskQueue::RegisterShutdownTask(nsITargetShutdownTask* aTask) {
NS_ENSURE_ARG(aTask);
MonitorAutoLock mon(mQueueMonitor);
if (mIsShutdown) {
return NS_ERROR_UNEXPECTED;
}
MOZ_ASSERT(!mShutdownTasks.Contains(aTask));
mShutdownTasks.AppendElement(aTask);
return NS_OK;
}
nsresult TaskQueue::UnregisterShutdownTask(nsITargetShutdownTask* aTask) {
NS_ENSURE_ARG(aTask);
MonitorAutoLock mon(mQueueMonitor);
if (mIsShutdown) {
return NS_ERROR_UNEXPECTED;
}
return mShutdownTasks.RemoveElement(aTask) ? NS_OK : NS_ERROR_UNEXPECTED;
}
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.IsEmpty());
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);
// Dispatch any cleanup tasks to the queue before we put it into full
// shutdown.
for (auto& task : mShutdownTasks) {
nsCOMPtr runnable{task->AsRunnable()};
MOZ_ALWAYS_SUCCEEDS(
DispatchLocked(runnable, NS_DISPATCH_NORMAL, TailDispatch));
}
mShutdownTasks.Clear();
mIsShutdown = true;
RefPtr<ShutdownPromise> p = mShutdownPromise.Ensure(__func__);
MaybeResolveShutdown();
mon.NotifyAll();
return p;
}
void TaskQueue::MaybeResolveShutdown() {
mQueueMonitor.AssertCurrentThreadOwns();
if (mIsShutdown && !mIsRunning) {
mShutdownPromise.ResolveIfExists(true, __func__);
// Disconnect from our target as we won't try to dispatch any more events.
mTrackerEntry = nullptr;
mTarget = nullptr;
}
}
bool TaskQueue::IsEmpty() {
MonitorAutoLock mon(mQueueMonitor);
return mTasks.IsEmpty();
}
bool TaskQueue::IsCurrentThreadIn() const {
bool in = mRunningThread == PR_GetCurrentThread();
return in;
}
nsresult TaskQueue::Runner::Run() {
TaskStruct event;
{
MonitorAutoLock mon(mQueue->mQueueMonitor);
MOZ_ASSERT(mQueue->mIsRunning);
if (mQueue->mTasks.IsEmpty()) {
mQueue->mIsRunning = false;
mQueue->MaybeResolveShutdown();
mon.NotifyAll();
return NS_OK;
}
event = mQueue->mTasks.Pop();
}
MOZ_ASSERT(event.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);
SerialEventTargetGuard tg(mQueue);
{
LogRunnable::Run log(event.event);
AUTO_PROFILE_FOLLOWING_RUNNABLE(event.event);
event.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.event = nullptr;
}
}
{
MonitorAutoLock mon(mQueue->mQueueMonitor);
if (mQueue->mTasks.IsEmpty()) {
// 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;
{
MonitorAutoLock mon(mQueue->mQueueMonitor);
rv = mQueue->mTarget->Dispatch(
this, mQueue->mTasks.FirstElement().flags | 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;
}
//-----------------------------------------------------------------------------
// nsIDirectTaskDispatcher
//-----------------------------------------------------------------------------
NS_IMETHODIMP
TaskQueue::DispatchDirectTask(already_AddRefed<nsIRunnable> aEvent) {
if (!IsCurrentThreadIn()) {
return NS_ERROR_FAILURE;
}
mDirectTasks.AddTask(std::move(aEvent));
return NS_OK;
}
NS_IMETHODIMP TaskQueue::DrainDirectTasks() {
if (!IsCurrentThreadIn()) {
return NS_ERROR_FAILURE;
}
mDirectTasks.DrainTasks();
return NS_OK;
}
NS_IMETHODIMP TaskQueue::HaveDirectTasks(bool* aValue) {
if (!IsCurrentThreadIn()) {
return NS_ERROR_FAILURE;
}
*aValue = mDirectTasks.HaveTasks();
return NS_OK;
}
nsTArray<RefPtr<TaskQueue>> TaskQueueTracker::GetAllTrackedTaskQueues() {
MutexAutoLock lock(mMutex);
nsTArray<RefPtr<TaskQueue>> queues;
for (auto* entry : mEntries) {
if (auto queue = entry->GetQueue()) {
queues.AppendElement(queue);
}
}
return queues;
}
TaskQueueTracker::~TaskQueueTracker() = default;
} // namespace mozilla