gecko-dev/netwerk/ipc/ChannelEventQueue.h

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 * Version: MPL 1.1/GPL 2.0/LGPL 2.1
 *
 * The contents of this file are subject to the Mozilla Public License Version
 * 1.1 (the "License"); you may not use this file except in compliance with
 * the License. You may obtain a copy of the License at:
 * http://www.mozilla.org/MPL/
 *
 * Software distributed under the License is distributed on an "AS IS" basis,
 * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
 * for the specific language governing rights and limitations under the
 * License.
 *
 * The Original Code is Mozilla Code.
 *
 * The Initial Developer of the Original Code is
 *   The Mozilla Foundation
 * Portions created by the Initial Developer are Copyright (C) 2010
 * the Initial Developer. All Rights Reserved.
 *
 * Contributor(s):
 *   Josh Matthews <josh@joshmatthews.net> (initial developer)
 *
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 * either the GNU General Public License Version 2 or later (the "GPL"), or
 * the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
 * in which case the provisions of the GPL or the LGPL are applicable instead
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 * ***** END LICENSE BLOCK ***** */

#ifndef mozilla_net_ChannelEventQueue_h
#define mozilla_net_ChannelEventQueue_h

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 called before mListener->OnStartRequest has completed.

template<class T> class AutoEventEnqueuerBase;

template<class T>
class ChannelEventQueue
{
 public:
  ChannelEventQueue(T* self) : mQueuePhase(PHASE_UNQUEUED)
                             , mSelf(self) {}
  ~ChannelEventQueue() {}
  
 protected:
  void BeginEventQueueing();
  void EndEventQueueing();
  void EnqueueEvent(ChannelEvent* callback);
  bool ShouldEnqueue();
  void FlushEventQueue();

  nsTArray<nsAutoPtr<ChannelEvent> > mEventQueue;
  enum {
    PHASE_UNQUEUED,
    PHASE_QUEUEING,
    PHASE_FINISHED_QUEUEING,
    PHASE_FLUSHING
  } mQueuePhase;

  typedef AutoEventEnqueuerBase<T> AutoEventEnqueuer;

 private:
  T* mSelf;

  friend class AutoEventEnqueuerBase<T>;
};

template<class T> inline void
ChannelEventQueue<T>::BeginEventQueueing()
{
  if (mQueuePhase != PHASE_UNQUEUED)
    return;
  // Store incoming IPDL messages for later.
  mQueuePhase = PHASE_QUEUEING;
}

template<class T> inline void
ChannelEventQueue<T>::EndEventQueueing()
{
  if (mQueuePhase != PHASE_QUEUEING)
    return;

  mQueuePhase = PHASE_FINISHED_QUEUEING;
}

template<class T> inline bool
ChannelEventQueue<T>::ShouldEnqueue()
{
  return mQueuePhase != PHASE_UNQUEUED || mSelf->IsSuspended();
}

template<class T> inline void
ChannelEventQueue<T>::EnqueueEvent(ChannelEvent* callback)
{
  mEventQueue.AppendElement(callback);
}

template<class T> void
ChannelEventQueue<T>::FlushEventQueue()
{
  NS_ABORT_IF_FALSE(mQueuePhase != PHASE_UNQUEUED,
                    "Queue flushing should not occur if PHASE_UNQUEUED");
  
  // Queue already being flushed
  if (mQueuePhase != PHASE_FINISHED_QUEUEING || mSelf->IsSuspended())
    return;
  
  nsRefPtr<T> kungFuDeathGrip(mSelf);
  if (mEventQueue.Length() > 0) {
    // It is possible for new callbacks to be enqueued as we are
    // flushing the queue, so the queue must not be cleared until
    // all callbacks have run.
    mQueuePhase = PHASE_FLUSHING;
    
    PRUint32 i;
    for (i = 0; i < mEventQueue.Length(); i++) {
      mEventQueue[i]->Run();
      if (mSelf->IsSuspended())
        break;
    }

    // We will always want to remove at least one finished callback.
    if (i < mEventQueue.Length())
      i++;

    mEventQueue.RemoveElementsAt(0, i);
  }

  if (mSelf->IsSuspended())
    mQueuePhase = PHASE_QUEUEING;
  else
    mQueuePhase = PHASE_UNQUEUED;
}

// Ensures any incoming IPDL msgs are queued during its lifetime, and flushes
// the queue when it goes out of scope.
template<class T>
class AutoEventEnqueuerBase
{
 public:
  AutoEventEnqueuerBase(ChannelEventQueue<T>* queue) : mEventQueue(queue) 
  {
    mEventQueue->BeginEventQueueing();
  }
  ~AutoEventEnqueuerBase() 
  { 
    mEventQueue->EndEventQueueing();
    mEventQueue->FlushEventQueue(); 
  }
 private:
  ChannelEventQueue<T> *mEventQueue;
};

}
}

#endif