Bug 947632 - Assert that we don't sendSyncMessage while processing a CPOW request (r=dvander)

ipc/glue/MessageChannel.cpp

@@ -57,6 +57,7 @@ MessageChannel::MessageChannel(MessageListener *aListener)
     mPendingRPCReplies(0),
     mCurrentRPCTransaction(0),
     mDispatchingSyncMessage(false),
+    mDispatchingUrgentMessageCount(0),
     mRemoteStackDepthGuess(false),
     mSawInterruptOutMsg(false)
 {
@@ -416,6 +417,7 @@ MessageChannel::Send(Message* aMsg, Message* aReply)
 
     IPC_ASSERT(aMsg->is_sync(), "can only Send() sync messages here");
     IPC_ASSERT(!DispatchingSyncMessage(), "violation of sync handler invariant");
+    IPC_ASSERT(!DispatchingUrgentMessage(), "sync messages forbidden while handling urgent message");
     IPC_ASSERT(!AwaitingSyncReply(), "nested sync messages are not supported");
 
     AutoEnterPendingReply replies(mPendingSyncReplies);
@@ -937,7 +939,11 @@ MessageChannel::DispatchUrgentMessage(const Message& aMsg)
 
     Message *reply = nullptr;
 
-    if (!MaybeHandleError(mListener->OnCallReceived(aMsg, reply), "DispatchUrgentMessage")) {
+    mDispatchingUrgentMessageCount++;
+    Result rv = mListener->OnCallReceived(aMsg, reply);
+    mDispatchingUrgentMessageCount--;
+
+    if (!MaybeHandleError(rv, "DispatchUrgentMessage")) {
         delete reply;
         reply = new Message();
         reply->set_urgent();

ipc/glue/MessageChannel.h

@@ -384,6 +384,11 @@ class MessageChannel : HasResultCodes
         return mDispatchingSyncMessage;
     }
 
+    // Returns true if we're dispatching an urgent message's callback.
+    bool DispatchingUrgentMessage() const {
+        return mDispatchingUrgentMessageCount > 0;
+    }
+
     bool Connected() const;
 
   private:
@@ -576,6 +581,9 @@ class MessageChannel : HasResultCodes
     // Set while we are dispatching a synchronous message.
     bool mDispatchingSyncMessage;
 
+    // Count of the recursion depth of dispatching urgent messages.
+    size_t mDispatchingUrgentMessageCount;
+
     // Queue of all incoming messages, except for replies to sync and urgent
     // messages, which are delivered directly to mRecvd, and any pending urgent
     // incall, which is stored in mPendingUrgentRequest.