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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 http://mozilla.org/MPL/2.0/. */
#ifndef mozilla_SynchronizedEventQueue_h
#define mozilla_SynchronizedEventQueue_h
#include "mozilla/AlreadyAddRefed.h"
#include "mozilla/EventQueue.h"
#include "mozilla/MemoryReporting.h"
#include "mozilla/Mutex.h"
#include "nsIThreadInternal.h"
#include "nsCOMPtr.h"
#include "nsTObserverArray.h"
class nsIEventTarget;
class nsISerialEventTarget;
class nsIThreadObserver;
namespace mozilla {
// A SynchronizedEventQueue is an abstract class for event queues that can be
// used across threads. A SynchronizedEventQueue implementation will typically
// use locks and condition variables to guarantee consistency. The methods of
// SynchronizedEventQueue are split between ThreadTargetSink (which contains
// methods for posting events) and SynchronizedEventQueue (which contains
// methods for getting events). This split allows event targets (specifically
// ThreadEventTarget) to use a narrow interface, since they only need to post
// events.
//
// ThreadEventQueue is the canonical implementation of
// SynchronizedEventQueue. When Quantum DOM is implemented, we will use a
// different synchronized queue on the main thread, SchedulerEventQueue, which
// will handle the cooperative threading model.
class ThreadTargetSink {
public:
NS_INLINE_DECL_THREADSAFE_REFCOUNTING(ThreadTargetSink)
virtual bool PutEvent(already_AddRefed<nsIRunnable>&& aEvent,
EventQueuePriority aPriority) = 0;
// After this method is called, no more events can be posted.
virtual void Disconnect(const MutexAutoLock& aProofOfLock) = 0;
virtual nsresult RegisterShutdownTask(nsITargetShutdownTask* aTask) = 0;
virtual nsresult UnregisterShutdownTask(nsITargetShutdownTask* aTask) = 0;
size_t SizeOfIncludingThis(mozilla::MallocSizeOf aMallocSizeOf) {
return aMallocSizeOf(this) + SizeOfExcludingThis(aMallocSizeOf);
}
// Not const because overrides may need to take a lock
virtual size_t SizeOfExcludingThis(mozilla::MallocSizeOf aMallocSizeOf) = 0;
protected:
virtual ~ThreadTargetSink() = default;
};
class SynchronizedEventQueue : public ThreadTargetSink {
public:
virtual already_AddRefed<nsIRunnable> GetEvent(
bool aMayWait, mozilla::TimeDuration* aLastEventDelay = nullptr) = 0;
virtual bool HasPendingEvent() = 0;
// This method atomically checks if there are pending events and, if there are
// none, forbids future events from being posted. It returns true if there
// were no pending events.
virtual bool ShutdownIfNoPendingEvents() = 0;
// These methods provide access to an nsIThreadObserver, whose methods are
// called when posting and processing events. SetObserver should only be
// called on the thread that processes events. GetObserver can be called from
// any thread. GetObserverOnThread must be used from the thread that processes
// events; it does not acquire a lock.
virtual already_AddRefed<nsIThreadObserver> GetObserver() = 0;
virtual already_AddRefed<nsIThreadObserver> GetObserverOnThread() = 0;
virtual void SetObserver(nsIThreadObserver* aObserver) = 0;
void AddObserver(nsIThreadObserver* aObserver);
void RemoveObserver(nsIThreadObserver* aObserver);
const nsTObserverArray<nsCOMPtr<nsIThreadObserver>>& EventObservers();
size_t SizeOfExcludingThis(mozilla::MallocSizeOf aMallocSizeOf) override {
// Normally we'd return
// mEventObservers.ShallowSizeOfExcludingThis(aMallocSizeOf); However,
// mEventObservers may be being mutated on another thread, and we don't lock
// around access, so locking here wouldn't help. They're small, so
return 0;
}
/**
* This method causes any events currently enqueued on the thread to be
* suppressed until PopEventQueue is called, and any event dispatched to this
* thread's nsIEventTarget will queue as well. Calls to PushEventQueue may be
* nested and must each be paired with a call to PopEventQueue in order to
* restore the original state of the thread. The returned nsIEventTarget may
* be used to push events onto the nested queue. Dispatching will be disabled
* once the event queue is popped. The thread will only ever process pending
* events for the innermost event queue. Must only be called on the target
* thread.
*/
virtual already_AddRefed<nsISerialEventTarget> PushEventQueue() = 0;
/**
* Revert a call to PushEventQueue. When an event queue is popped, any events
* remaining in the queue are appended to the elder queue. This also causes
* the nsIEventTarget returned from PushEventQueue to stop dispatching events.
* Must only be called on the target thread, and with the innermost event
* queue.
*/
virtual void PopEventQueue(nsIEventTarget* aTarget) = 0;
/**
* Flush the list of shutdown tasks which were previously registered. After
* this is called, new shutdown tasks cannot be registered.
*/
virtual void RunShutdownTasks() = 0;
protected:
virtual ~SynchronizedEventQueue() = default;
private:
nsTObserverArray<nsCOMPtr<nsIThreadObserver>> mEventObservers;
};
} // namespace mozilla
#endif // mozilla_SynchronizedEventQueue_h
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