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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
* file, You can obtain one at */
#include "nsMessageLoop.h"
#include "mozilla/WeakPtr.h"
#include "base/message_loop.h"
#include "base/task.h"
#include "nsINamed.h"
#include "nsIRunnable.h"
#include "nsITimer.h"
#include "nsCOMPtr.h"
#include "nsComponentManagerUtils.h"
#include "nsThreadUtils.h"
using namespace mozilla;
namespace {
* This Task runs its nsIRunnable when Run() is called, or after
* aEnsureRunsAfterMS milliseconds have elapsed since the object was
* constructed.
* Note that the MessageLoop owns this object and will delete it after it calls
* Run(). Tread lightly.
class MessageLoopIdleTask : public Runnable, public SupportsWeakPtr {
MessageLoopIdleTask(nsIRunnable* aTask, uint32_t aEnsureRunsAfterMS);
NS_IMETHOD Run() override;
nsresult Init(uint32_t aEnsureRunsAfterMS);
nsCOMPtr<nsIRunnable> mTask;
nsCOMPtr<nsITimer> mTimer;
virtual ~MessageLoopIdleTask() = default;
* This timer callback calls MessageLoopIdleTask::Run() when its timer fires.
* (The timer can't call back into MessageLoopIdleTask directly since that's
* not a refcounted object; it's owned by the MessageLoop.)
* We keep a weak reference to the MessageLoopIdleTask, although a raw pointer
* should in theory suffice: When the MessageLoopIdleTask runs (right before
* the MessageLoop deletes it), it cancels its timer. But the weak pointer
* saves us from worrying about an edge case somehow messing us up here.
class MessageLoopTimerCallback : public nsITimerCallback, public nsINamed {
explicit MessageLoopTimerCallback(MessageLoopIdleTask* aTask);
NS_IMETHOD GetName(nsACString& aName) override {
return NS_OK;
WeakPtr<MessageLoopIdleTask> mTask;
virtual ~MessageLoopTimerCallback() = default;
MessageLoopIdleTask::MessageLoopIdleTask(nsIRunnable* aTask,
uint32_t aEnsureRunsAfterMS)
: mozilla::Runnable("MessageLoopIdleTask"), mTask(aTask) {
// Init() really shouldn't fail, but if it does, we schedule our runnable
// immediately, because it's more important to guarantee that we run the task
// eventually than it is to run the task when we're idle.
nsresult rv = Init(aEnsureRunsAfterMS);
if (NS_FAILED(rv)) {
"Running idle task early because we couldn't initialize our timer.");
mTask = nullptr;
mTimer = nullptr;
nsresult MessageLoopIdleTask::Init(uint32_t aEnsureRunsAfterMS) {
RefPtr<MessageLoopTimerCallback> callback =
new MessageLoopTimerCallback(this);
return NS_NewTimerWithCallback(getter_AddRefs(mTimer), callback,
aEnsureRunsAfterMS, nsITimer::TYPE_ONE_SHOT);
MessageLoopIdleTask::Run() {
// Null out our pointers because if Run() was called by the timer, this
// object will be kept alive by the MessageLoop until the MessageLoop calls
// Run().
if (mTimer) {
mTimer = nullptr;
if (mTask) {
mTask = nullptr;
return NS_OK;
MessageLoopTimerCallback::MessageLoopTimerCallback(MessageLoopIdleTask* aTask)
: mTask(aTask) {}
MessageLoopTimerCallback::Notify(nsITimer* aTimer) {
// We don't expect to hit the case when the timer fires but mTask has been
// deleted, because mTask should cancel the timer before the mTask is
// deleted. But you never know...
NS_WARNING_ASSERTION(mTask, "This timer shouldn't have fired.");
if (mTask) {
return NS_OK;
NS_IMPL_ISUPPORTS(MessageLoopTimerCallback, nsITimerCallback, nsINamed)
} // namespace
NS_IMPL_ISUPPORTS(nsMessageLoop, nsIMessageLoop)
nsMessageLoop::PostIdleTask(nsIRunnable* aTask, uint32_t aEnsureRunsAfterMS) {
// The message loop owns MessageLoopIdleTask and deletes it after calling
// Run(). Be careful...
RefPtr<MessageLoopIdleTask> idle =
new MessageLoopIdleTask(aTask, aEnsureRunsAfterMS);
return NS_OK;
nsresult nsMessageLoopConstructor(nsISupports* aOuter, const nsIID& aIID,
void** aInstancePtr) {
if (NS_WARN_IF(aOuter)) {
nsISupports* messageLoop = new nsMessageLoop();
return messageLoop->QueryInterface(aIID, aInstancePtr);