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>
class nsISupports;
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 AutoEventEnqueuerBase;
class ChannelEventQueue
{
public:
ChannelEventQueue(nsISupports *owner)
: mForced(false)
, mSuspended(false)
, mFlushing(false)
, mOwner(owner) {}
~ChannelEventQueue() {}
// Checks to determine if an IPDL-generated channel event can be processed
// immediately, or needs to be queued using Enqueue().
inline bool ShouldEnqueue();
// Puts IPDL-generated channel event into queue, to be run later
// automatically when EndForcedQueueing and/or Resume is called.
inline void Enqueue(ChannelEvent* callback);
// After StartForcedQueueing is called, ShouldEnqueue() will return true and
// no events will be run/flushed until EndForcedQueueing is called.
// - Note: queueing may still be required after EndForcedQueueing() (if the
// queue is suspended, etc): always call ShouldEnqueue() to determine
// whether queueing is needed.
inline void StartForcedQueueing();
inline void EndForcedQueueing();
// Suspend/resume event queue. ShouldEnqueue() will return true and no events
// will be run/flushed until resume is called. These should be called when
// the channel owning the event queue is suspended/resumed.
// - Note: these suspend/resume functions are NOT meant to be called
// recursively: call them only at initial suspend, and actual resume).
// - Note: Resume flushes the queue and invokes any pending callbacks
// immediately--caller must arrange any needed asynchronicity vis a vis
// the channel's own Resume() method.
inline void Suspend();
inline void Resume();
private:
inline void MaybeFlushQueue();
void FlushQueue();
nsTArray<nsAutoPtr<ChannelEvent> > mEventQueue;
bool mForced;
bool mSuspended;
bool mFlushing;
// Keep ptr to avoid refcount cycle: only grab ref during flushing.
nsISupports *mOwner;
friend class AutoEventEnqueuer;
};
inline bool
ChannelEventQueue::ShouldEnqueue()
{
bool answer = mForced || mSuspended || mFlushing;
NS_ABORT_IF_FALSE(answer == true || mEventQueue.IsEmpty(),
"Should always enqueue if ChannelEventQueue not empty");
return answer;
}
inline void
ChannelEventQueue::Enqueue(ChannelEvent* callback)
{
mEventQueue.AppendElement(callback);
}
inline void
ChannelEventQueue::StartForcedQueueing()
{
mForced = true;
}
inline void
ChannelEventQueue::EndForcedQueueing()
{
mForced = false;
MaybeFlushQueue();
}
inline void
ChannelEventQueue::Suspend()
{
NS_ABORT_IF_FALSE(!mSuspended,
"ChannelEventQueue::Suspend called recursively");
mSuspended = true;
}
inline void
ChannelEventQueue::Resume()
{
NS_ABORT_IF_FALSE(mSuspended,
"ChannelEventQueue::Resume called when not suspended!");
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
if (!mForced && !mFlushing && !mSuspended && !mEventQueue.IsEmpty())
FlushQueue();
}
// Ensures that ShouldEnqueue() will be true during its lifetime (letting
// caller know incoming IPDL msgs should be queued). Flushes the queue when it
// goes out of scope.
class AutoEventEnqueuer
{
public:
AutoEventEnqueuer(ChannelEventQueue &queue) : mEventQueue(queue) {
mEventQueue.StartForcedQueueing();
}
~AutoEventEnqueuer() {
mEventQueue.EndForcedQueueing();
}
private:
ChannelEventQueue &mEventQueue;
};
}
}
#endif