Bug 1405962. P1 - give MediaCache a thread on which we will run data callbacks from the HTTP channel. r=gerald

MozReview-Commit-ID: Av7bFGx9SW

--HG--
extra : rebase_source : 296a6137ee63328e11eb11a8ee3430979cf8e5a8
extra : intermediate-source : 9634a9cd63e188799fe691cfe7108a173db503d5
extra : source : 43860a593eb810088adac150c0fa85cf8133ce17

dom/media/ChannelMediaResource.cpp

@@ -10,6 +10,7 @@
 #include "nsICachingChannel.h"
 #include "nsIClassOfService.h"
 #include "nsIInputStream.h"
+#include "nsIThreadRetargetableRequest.h"
 #include "nsNetUtil.h"
 
 static const uint32_t HTTP_PARTIAL_RESPONSE_CODE = 206;
@@ -299,6 +300,16 @@ ChannelMediaResource::OnStartRequest(nsIRequest* aRequest,
   // Fires an initial progress event.
   owner->DownloadProgressed();
 
+  // TODO: Don't turn this on until we fix all data races.
+  nsCOMPtr<nsIThreadRetargetableRequest> retarget;
+  if (Preferences::GetBool("media.omt_data_delivery.enabled", false) &&
+      (retarget = do_QueryInterface(aRequest)) && mCacheStream.OwnerThread()) {
+    // Note this will not always succeed. We need to handle the case where
+    // all resources sharing the same cache might run their data callbacks
+    // on different threads.
+    retarget->RetargetDeliveryTo(mCacheStream.OwnerThread());
+  }
+
   return NS_OK;
 }
 

dom/media/MediaCache.cpp

@@ -151,6 +151,8 @@ public:
   // file backing will be provided.
   static RefPtr<MediaCache> GetMediaCache(int64_t aContentLength);
 
+  nsIEventTarget* OwnerThread() const { return mThread; }
+
   // Brutally flush the cache contents. Main thread only.
   void Flush();
 
@@ -277,6 +279,10 @@ protected:
     NS_ASSERTION(NS_IsMainThread(), "Only construct MediaCache on main thread");
     MOZ_COUNT_CTOR(MediaCache);
     MediaCacheFlusher::RegisterMediaCache(this);
+    nsresult rv = NS_NewNamedThread("MediaCache", getter_AddRefs(mThread));
+    if (NS_FAILED(rv)) {
+      NS_WARNING("Failed to create a thread for MediaCache.");
+    }
   }
 
   ~MediaCache()
@@ -308,6 +314,11 @@ protected:
     Truncate();
     NS_ASSERTION(mIndex.Length() == 0, "Blocks leaked?");
 
+    nsCOMPtr<nsIThread> thread = mThread.forget();
+    if (thread) {
+      thread->Shutdown();
+    }
+
     MOZ_COUNT_DTOR(MediaCache);
   }
 
@@ -436,6 +447,9 @@ protected:
 #endif
   // A list of resource IDs to notify about the change in suspended status.
   nsTArray<int64_t> mSuspendedStatusToNotify;
+  // The thread on which we will run data callbacks from the channels.
+  // Could be null if failing to create the thread.
+  nsCOMPtr<nsIThread> mThread;
 };
 
 // Initialized to nullptr by non-local static initialization.
@@ -1939,11 +1953,6 @@ MediaCacheStream::NotifyDataReceived(uint32_t aLoadID,
       aSize,
       aLoadID);
 
-  // TODO: For now NotifyDataReceived() always runs on the main thread. This
-  // assertion is to make sure our load ID algorithm doesn't go wrong. Remove it
-  // when OMT data delievery is enabled.
-  MOZ_DIAGNOSTIC_ASSERT(mLoadID == aLoadID);
-
   if (mLoadID != aLoadID) {
     // mChannelOffset is updated to a new position when loading a new channel.
     // We should discard the data coming from the old channel so it won't be
@@ -2662,6 +2671,12 @@ MediaCacheStream::InitAsClone(MediaCacheStream* aOriginal)
   }
 }
 
+nsIEventTarget*
+MediaCacheStream::OwnerThread() const
+{
+  return mMediaCache->OwnerThread();
+}
+
 nsresult MediaCacheStream::GetCachedRanges(MediaByteRangeSet& aRanges)
 {
   // Take the monitor, so that the cached data ranges can't grow while we're

dom/media/MediaCache.h

@@ -14,6 +14,7 @@
 #include "nsTArray.h"
 #include "nsTHashtable.h"
 
+class nsIEventTarget;
 class nsIPrincipal;
 
 namespace mozilla {
@@ -210,6 +211,8 @@ public:
   // on this class.
   void InitAsClone(MediaCacheStream* aOriginal);
 
+  nsIEventTarget* OwnerThread() const;
+
   // These are called on the main thread.
   // Tell us whether the stream is seekable or not. Non-seekable streams
   // will always pass 0 for aOffset to CacheClientSeek. This should only

modules/libpref/init/all.js

@@ -311,6 +311,10 @@ pref("mathml.scale_stretchy_operators.enabled", true);
 
 pref("media.dormant-on-pause-timeout-ms", 5000);
 
+// Used by ChannelMediaResource to run data callbacks from HTTP channel
+// off the main thread.
+pref("media.omt_data_delivery.enabled", false);
+
 // File-backed MediaCache size in kilobytes
 pref("media.cache_size", 512000);
 // When a network connection is suspended, don't resume it until the