gecko-dev/netwerk/ipc/ChannelEventQueue.h

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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
* vim: set sw=2 ts=8 et 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_net_ChannelEventQueue_h
#define mozilla_net_ChannelEventQueue_h
#include "nsTArray.h"
#include "nsAutoPtr.h"
#include "mozilla/Mutex.h"
#include "mozilla/UniquePtr.h"
class nsISupports;
class nsIEventTarget;
namespace mozilla {
namespace net {
class ChannelEvent
{
public:
ChannelEvent() { MOZ_COUNT_CTOR(ChannelEvent); }
virtual ~ChannelEvent() { MOZ_COUNT_DTOR(ChannelEvent); }
virtual void Run() = 0;
};
// Workaround for Necko re-entrancy dangers. We buffer IPDL messages in a
// queue if still dispatching previous one(s) to listeners/observers.
// Otherwise synchronous XMLHttpRequests and/or other code that spins the
// event loop (ex: IPDL rpc) could cause listener->OnDataAvailable (for
// instance) to be dispatched and called before mListener->OnStartRequest has
// completed.
class ChannelEventQueue final
{
NS_INLINE_DECL_THREADSAFE_REFCOUNTING(ChannelEventQueue)
public:
explicit ChannelEventQueue(nsISupports *owner)
: mSuspendCount(0)
, mSuspended(false)
, mForced(false)
, mFlushing(false)
, mOwner(owner)
, mMutex("ChannelEventQueue::mMutex")
{}
// Puts IPDL-generated channel event into queue, to be run later
// automatically when EndForcedQueueing and/or Resume is called.
//
// @param aCallback - the ChannelEvent
// @param aAssertionWhenNotQueued - this optional param will be used in an
// assertion when the event is executed directly.
inline void RunOrEnqueue(ChannelEvent* aCallback,
bool aAssertionWhenNotQueued = false);
inline nsresult PrependEvents(nsTArray<UniquePtr<ChannelEvent>>& aEvents);
// After StartForcedQueueing is called, RunOrEnqueue() will start enqueuing
// events that will be run/flushed when EndForcedQueueing is called.
// - Note: queueing may still be required after EndForcedQueueing() (if the
// queue is suspended, etc): always call RunOrEnqueue() to avoid race
// conditions.
inline void StartForcedQueueing();
inline void EndForcedQueueing();
// Suspend/resume event queue. RunOrEnqueue() will start enqueuing
// events and they will be run/flushed when resume is called. These should be
// called when the channel owning the event queue is suspended/resumed.
inline void Suspend();
// Resume flushes the queue asynchronously, i.e. items in queue will be
// dispatched in a new event on the current thread.
void Resume();
// Retargets delivery of events to the target thread specified.
nsresult RetargetDeliveryTo(nsIEventTarget* aTargetThread);
private:
// Private destructor, to discourage deletion outside of Release():
~ChannelEventQueue()
{
}
inline void MaybeFlushQueue();
void FlushQueue();
inline void CompleteResume();
ChannelEvent* TakeEvent();
nsTArray<UniquePtr<ChannelEvent>> mEventQueue;
uint32_t mSuspendCount;
bool mSuspended;
bool mForced;
bool mFlushing;
// Keep ptr to avoid refcount cycle: only grab ref during flushing.
nsISupports *mOwner;
Mutex mMutex;
// EventTarget for delivery of events to the correct thread.
nsCOMPtr<nsIEventTarget> mTargetThread;
friend class AutoEventEnqueuer;
};
inline void
ChannelEventQueue::RunOrEnqueue(ChannelEvent* aCallback,
bool aAssertionWhenNotQueued)
{
MOZ_ASSERT(aCallback);
// To avoid leaks.
UniquePtr<ChannelEvent> event(aCallback);
{
MutexAutoLock lock(mMutex);
bool enqueue = mForced || mSuspended || mFlushing;
MOZ_ASSERT(enqueue == true || mEventQueue.IsEmpty(),
"Should always enqueue if ChannelEventQueue not empty");
if (enqueue) {
mEventQueue.AppendElement(Move(event));
return;
}
}
MOZ_RELEASE_ASSERT(!aAssertionWhenNotQueued);
event->Run();
}
inline void
ChannelEventQueue::StartForcedQueueing()
{
MutexAutoLock lock(mMutex);
mForced = true;
}
inline void
ChannelEventQueue::EndForcedQueueing()
{
{
MutexAutoLock lock(mMutex);
mForced = false;
}
MaybeFlushQueue();
}
inline nsresult
ChannelEventQueue::PrependEvents(nsTArray<UniquePtr<ChannelEvent>>& aEvents)
{
MutexAutoLock lock(mMutex);
UniquePtr<ChannelEvent>* newEvents =
mEventQueue.InsertElementsAt(0, aEvents.Length());
if (!newEvents) {
return NS_ERROR_OUT_OF_MEMORY;
}
for (uint32_t i = 0; i < aEvents.Length(); i++) {
newEvents[i] = Move(aEvents[i]);
}
return NS_OK;
}
inline void
ChannelEventQueue::Suspend()
{
MutexAutoLock lock(mMutex);
mSuspended = true;
mSuspendCount++;
}
inline void
ChannelEventQueue::CompleteResume()
{
{
MutexAutoLock lock(mMutex);
// channel may have been suspended again since Resume fired event to call
// this.
if (!mSuspendCount) {
// we need to remain logically suspended (for purposes of queuing incoming
// messages) until this point, else new incoming messages could run before
// queued ones.
mSuspended = false;
}
}
MaybeFlushQueue();
}
inline void
ChannelEventQueue::MaybeFlushQueue()
{
// Don't flush if forced queuing on, we're already being flushed, or
// suspended, or there's nothing to flush
bool flushQueue = false;
{
MutexAutoLock lock(mMutex);
flushQueue = !mForced && !mFlushing && !mSuspended &&
!mEventQueue.IsEmpty();
}
if (flushQueue) {
FlushQueue();
}
}
// Ensures that RunOrEnqueue() will be collecting events during its lifetime
// (letting caller know incoming IPDL msgs should be queued). Flushes the queue
// when it goes out of scope.
class MOZ_STACK_CLASS AutoEventEnqueuer
{
public:
explicit AutoEventEnqueuer(ChannelEventQueue *queue) : mEventQueue(queue) {
mEventQueue->StartForcedQueueing();
}
~AutoEventEnqueuer() {
mEventQueue->EndForcedQueueing();
}
private:
RefPtr<ChannelEventQueue> mEventQueue;
};
} // namespace net
} // namespace mozilla
#endif