Bug 1357244. P2 - enforce the invariant that a block is in mFreeBlocks iff it has no owners. r=gerald

http://searchfox.org/mozilla-central/rev/4bd7a206dea5382c97a8a0c30beef668cc449f5b/dom/media/MediaCache.cpp#1529
Note we might return here with mOwners is empty and break the invariant.

MozReview-Commit-ID: JC5OtEU0B8O

--HG--
extra : rebase_source : f842601db12e047fd73a9b062612da2f2b7c0263

dom/media/MediaCache.cpp

@@ -1519,36 +1519,44 @@ MediaCache::AllocateAndWriteBlock(
     LOG("Allocated block %d to stream %p block %d(%" PRId64 ")",
         blockIndex, aStream, streamBlockIndex, streamBlockIndex*BLOCK_SIZE);
 
-    mFreeBlocks.RemoveBlock(blockIndex);
-
-    // Tell each stream using this resource about the new block.
     ResourceStreamIterator iter(aStream->mResourceID);
     while (MediaCacheStream* stream = iter.Next()) {
       BlockOwner* bo = block->mOwners.AppendElement();
-      if (!bo)
+      if (!bo) {
+        // Roll back mOwners if any allocation fails.
+        block->mOwners.Clear();
         return;
-
+      }
       bo->mStream = stream;
-      bo->mStreamBlock = streamBlockIndex;
-      bo->mLastUseTime = now;
-      stream->mBlocks[streamBlockIndex] = blockIndex;
-      if (streamBlockIndex*BLOCK_SIZE < stream->mStreamOffset) {
-        bo->mClass = aMode == MediaCacheStream::MODE_PLAYBACK ? PLAYED_BLOCK
-                                                              : METADATA_BLOCK;
+    }
+
+    // Tell each stream using this resource about the new block.
+    for (auto& bo : block->mOwners) {
+      bo.mStreamBlock = streamBlockIndex;
+      bo.mLastUseTime = now;
+      bo.mStream->mBlocks[streamBlockIndex] = blockIndex;
+      if (streamBlockIndex*BLOCK_SIZE < bo.mStream->mStreamOffset) {
+        bo.mClass = aMode == MediaCacheStream::MODE_PLAYBACK ? PLAYED_BLOCK
+                                                             : METADATA_BLOCK;
         // This must be the most-recently-used block, since we
         // marked it as used now (which may be slightly bogus, but we'll
         // treat it as used for simplicity).
-        GetListForBlock(bo)->AddFirstBlock(blockIndex);
+        GetListForBlock(&bo)->AddFirstBlock(blockIndex);
         Verify();
       } else {
         // This may not be the latest readahead block, although it usually
         // will be. We may have to scan for the right place to insert
         // the block in the list.
-        bo->mClass = READAHEAD_BLOCK;
-        InsertReadaheadBlock(bo, blockIndex);
+        bo.mClass = READAHEAD_BLOCK;
+        InsertReadaheadBlock(&bo, blockIndex);
       }
     }
 
+    // Invariant: block->mOwners.IsEmpty() iff we can find an entry
+    // in mFreeBlocks for a given blockIndex.
+    MOZ_DIAGNOSTIC_ASSERT(!block->mOwners.IsEmpty());
+    mFreeBlocks.RemoveBlock(blockIndex);
+
     nsresult rv = mFileCache->WriteBlock(blockIndex, aData1, aData2);
     if (NS_FAILED(rv)) {
       LOG("Released block %d from stream %p block %d(%" PRId64 ")",