1 files changed, 237 insertions, 0 deletions
diff --git a/netwerk/ipc/ChannelEventQueue.h b/netwerk/ipc/ChannelEventQueue.h
new file mode 100644
index 000000000..a843decab
--- /dev/null
+++ b/netwerk/ipc/ChannelEventQueue.h
@@ -0,0 +1,237 @@
+/* -*- 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