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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* 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/. */
#ifndef mozilla_lazyidlethread_h__
#define mozilla_lazyidlethread_h__
#ifndef MOZILLA_INTERNAL_API
#error "This header is only usable from within libxul (MOZILLA_INTERNAL_API)."
#endif
#include "nsIObserver.h"
#include "nsIThreadInternal.h"
#include "nsITimer.h"
#include "mozilla/Mutex.h"
#include "nsCOMPtr.h"
#include "nsTArray.h"
#include "nsString.h"
#include "mozilla/Attributes.h"
#define IDLE_THREAD_TOPIC "thread-shutting-down"
namespace mozilla {
/**
* This class provides a basic event target that creates its thread lazily and
* destroys its thread after a period of inactivity. It may be created on any
* thread but it may only be used from the thread on which it is created. If it
* is created on the main thread then it will automatically join its thread on
* XPCOM shutdown using the Observer Service.
*/
class LazyIdleThread final
: public nsIThread
, public nsITimerCallback
, public nsIThreadObserver
, public nsIObserver
{
public:
NS_DECL_THREADSAFE_ISUPPORTS
NS_DECL_NSIEVENTTARGET
NS_DECL_NSITHREAD
NS_DECL_NSITIMERCALLBACK
NS_DECL_NSITHREADOBSERVER
NS_DECL_NSIOBSERVER
using nsIEventTarget::Dispatch;
enum ShutdownMethod
{
AutomaticShutdown = 0,
ManualShutdown
};
/**
* Create a new LazyIdleThread that will destroy its thread after the given
* number of milliseconds.
*/
LazyIdleThread(uint32_t aIdleTimeoutMS,
const nsCSubstring& aName,
ShutdownMethod aShutdownMethod = AutomaticShutdown,
nsIObserver* aIdleObserver = nullptr);
/**
* Add an observer that will be notified when the thread is idle and about to
* be shut down. The aSubject argument can be QueryInterface'd to an nsIThread
* that can be used to post cleanup events. The aTopic argument will be
* IDLE_THREAD_TOPIC, and aData will be null. The LazyIdleThread does not add
* a reference to the observer to avoid circular references as it is assumed
* to be the owner. It is the caller's responsibility to clear this observer
* if the pointer becomes invalid.
*/
void SetWeakIdleObserver(nsIObserver* aObserver);
/**
* Disable the idle timeout for this thread. No effect if the timeout is
* already disabled.
*/
void DisableIdleTimeout();
/**
* Enable the idle timeout. No effect if the timeout is already enabled.
*/
void EnableIdleTimeout();
private:
/**
* Calls Shutdown().
*/
~LazyIdleThread();
/**
* Called just before dispatching to mThread.
*/
void PreDispatch();
/**
* Makes sure a valid thread lives in mThread.
*/
nsresult EnsureThread();
/**
* Called on mThread to set up the thread observer.
*/
void InitThread();
/**
* Called on mThread to clean up the thread observer.
*/
void CleanupThread();
/**
* Called on the main thread when mThread believes itself to be idle. Sets up
* the idle timer.
*/
void ScheduleTimer();
/**
* Called when we are shutting down mThread.
*/
nsresult ShutdownThread();
/**
* Deletes this object. Used to delay calling mThread->Shutdown() during the
* final release (during a GC, for instance).
*/
void SelfDestruct();
/**
* Returns true if events should be queued rather than immediately dispatched
* to mThread. Currently only happens when the thread is shutting down.
*/
bool UseRunnableQueue()
{
return !!mQueuedRunnables;
}
/**
* Protects data that is accessed on both threads.
*/
mozilla::Mutex mMutex;
/**
* Touched on both threads but set before mThread is created. Used to direct
* timer events to the owning thread.
*/
nsCOMPtr<nsIThread> mOwningThread;
/**
* Only accessed on the owning thread. Set by EnsureThread().
*/
nsCOMPtr<nsIThread> mThread;
/**
* Protected by mMutex. Created when mThread has no pending events and fired
* at mOwningThread. Any thread that dispatches to mThread will take ownership
* of the timer and fire a separate cancel event to the owning thread.
*/
nsCOMPtr<nsITimer> mIdleTimer;
/**
* Idle observer. Called when the thread is about to be shut down. Released
* only when Shutdown() is called.
*/
nsIObserver* MOZ_UNSAFE_REF("See the documentation for SetWeakIdleObserver for "
"how the owner of LazyIdleThread should manage the "
"lifetime information of this field") mIdleObserver;
/**
* Temporary storage for events that happen to be dispatched while we're in
* the process of shutting down our real thread.
*/
nsTArray<nsCOMPtr<nsIRunnable>>* mQueuedRunnables;
/**
* The number of milliseconds a thread should be idle before dying.
*/
const uint32_t mIdleTimeoutMS;
/**
* The number of events that are pending on mThread. A nonzero value means
* that the thread cannot be cleaned up.
*/
uint32_t mPendingEventCount;
/**
* The number of times that mThread has dispatched an idle notification. Any
* timer that fires while this count is nonzero can safely be ignored as
* another timer will be on the way.
*/
uint32_t mIdleNotificationCount;
/**
* Whether or not the thread should automatically shutdown. If the owner
* specified ManualShutdown at construction time then the owner should take
* care to call Shutdown() manually when appropriate.
*/
ShutdownMethod mShutdownMethod;
/**
* Only accessed on the owning thread. Set to true when Shutdown() has been
* called and prevents EnsureThread() from recreating mThread.
*/
bool mShutdown;
/**
* Set from CleanupThread and lasting until the thread has shut down. Prevents
* further idle notifications during the shutdown process.
*/
bool mThreadIsShuttingDown;
/**
* Whether or not the idle timeout is enabled.
*/
bool mIdleTimeoutEnabled;
/**
* Name of the thread, set on the actual thread after it gets created.
*/
nsCString mName;
};
} // namespace mozilla
#endif // mozilla_lazyidlethread_h__
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