From 1bffbe178b6d138e323fbec6184dbcf62bae28c9 Mon Sep 17 00:00:00 2001
From: Andreas Pehrson <pehrsons@gmail.com>
Date: Tue, 5 Jan 2016 10:16:22 +0800
Subject: [PATCH] Bug 1208371 - Count the users of a MediaStream to ease
 Destroy() responsibility. r=roc

MozReview-Commit-ID: FdcR4ChTND4

--HG--
extra : rebase_source : c0dfccffb686b483203b2906b734ae8b9459b924
---
 dom/media/MediaStreamGraph.cpp | 23 +++++++++++++++++++++++
 dom/media/MediaStreamGraph.h   | 14 +++++++++++++-
 2 files changed, 36 insertions(+), 1 deletion(-)

diff --git a/dom/media/MediaStreamGraph.cpp b/dom/media/MediaStreamGraph.cpp
index 4142d61e128c..fc07235e8ea7 100644
--- a/dom/media/MediaStreamGraph.cpp
+++ b/dom/media/MediaStreamGraph.cpp
@@ -1839,6 +1839,7 @@ MediaStream::MediaStream(DOMMediaStream* aWrapper)
   , mMainThreadFinished(false)
   , mFinishedNotificationSent(false)
   , mMainThreadDestroyed(false)
+  , mNrOfMainThreadUsers(0)
   , mGraph(nullptr)
   , mAudioChannelType(dom::AudioChannel::Normal)
 {
@@ -1982,6 +1983,8 @@ MediaStream::DestroyImpl()
 void
 MediaStream::Destroy()
 {
+  NS_ASSERTION(mNrOfMainThreadUsers == 0,
+               "Do not mix Destroy() and RegisterUser()/UnregisterUser()");
   // Keep this stream alive until we leave this method
   RefPtr<MediaStream> kungFuDeathGrip = this;
 
@@ -2006,6 +2009,26 @@ MediaStream::Destroy()
   mMainThreadDestroyed = true;
 }
 
+void
+MediaStream::RegisterUser()
+{
+  MOZ_ASSERT(NS_IsMainThread());
+  ++mNrOfMainThreadUsers;
+}
+
+void
+MediaStream::UnregisterUser()
+{
+  MOZ_ASSERT(NS_IsMainThread());
+
+  --mNrOfMainThreadUsers;
+  NS_ASSERTION(mNrOfMainThreadUsers >= 0, "Double-removal of main thread user");
+  NS_ASSERTION(!IsDestroyed(), "Do not mix Destroy() and RegisterUser()/UnregisterUser()");
+  if (mNrOfMainThreadUsers == 0) {
+    Destroy();
+  }
+}
+
 void
 MediaStream::AddAudioOutput(void* aKey)
 {
diff --git a/dom/media/MediaStreamGraph.h b/dom/media/MediaStreamGraph.h
index 964d45282134..aab74a9b94d6 100644
--- a/dom/media/MediaStreamGraph.h
+++ b/dom/media/MediaStreamGraph.h
@@ -431,8 +431,19 @@ public:
    */
   void RunAfterPendingUpdates(already_AddRefed<nsIRunnable> aRunnable);
 
-  // Signal that the client is done with this MediaStream. It will be deleted later.
+  // Signal that the client is done with this MediaStream. It will be deleted
+  // later. Do not mix usage of Destroy() with RegisterUser()/UnregisterUser().
+  // That will cause the MediaStream to be destroyed twice, which will cause
+  // some assertions to fail.
   virtual void Destroy();
+  // Signal that a client is using this MediaStream. Useful to not have to
+  // explicitly manage ownership (responsibility to Destroy()) when there are
+  // multiple clients using a MediaStream.
+  void RegisterUser();
+  // Signal that a client no longer needs this MediaStream. When the number of
+  // clients using this MediaStream reaches 0, it will be destroyed.
+  void UnregisterUser();
+
   // Returns the main-thread's view of how much data has been processed by
   // this stream.
   StreamTime GetCurrentTime()
@@ -706,6 +717,7 @@ protected:
   bool mMainThreadFinished;
   bool mFinishedNotificationSent;
   bool mMainThreadDestroyed;
+  int mNrOfMainThreadUsers;
 
   // Our media stream graph.  null if destroyed on the graph thread.
   MediaStreamGraphImpl* mGraph;