Introduce AudioSourceProviderClientLockScope.

Source/core/html/HTMLMediaElement.cpp

Index: Source/core/html/HTMLMediaElement.cpp
diff --git a/Source/core/html/HTMLMediaElement.cpp b/Source/core/html/HTMLMediaElement.cpp
index 2e7f9801e54e65cc38afbcd0fde33499f681174c..b234e8411837d157b7c2487d35177150e8f3863e 100644
--- a/Source/core/html/HTMLMediaElement.cpp
+++ b/Source/core/html/HTMLMediaElement.cpp
@@ -168,6 +168,30 @@ private:
     RawPtrWillBeMember<HTMLMediaElement> m_mediaElement;
 };
 
+class AudioSourceProviderClientLockScope {
+    STACK_ALLOCATED();
+public:
+#if ENABLE(WEB_AUDIO)
+    AudioSourceProviderClientLockScope(HTMLMediaElement& element)

[haraken, 2014/07/26 04:11:37]

Add explicit.

[tkent, 2014/07/28 01:20:55]

Done.

+        : m_client(element.audioSourceNode())
+    {
+        if (m_client)
+            m_client->lock();
+    }
+    ~AudioSourceProviderClientLockScope()
+    {
+        if (m_client)
+            m_client->unlock();
+    }
+
+private:
+    RawPtrWillBeMember<AudioSourceProviderClient> m_client;

[haraken, 2014/07/26 04:11:37]

I wonder if we can just use RefPtrWillBeMember<AudioSourceProviderClient> here
and remove manual ref()/deref() in MediaElementAudioSourceNode.cpp. Since
AudioSourceProviderClientLockScope is stack-allocated, there would be no risk
for the RefPtr to produce a cycle.

[tkent, 2014/07/28 01:20:55]

Done.  But do you think Patch Set 3 is better than Patch Set 2?

+#else
+    AudioSourceProviderClientLockScope(HTMLMediaElement&) { }
+    ~AudioSourceProviderClientLockScope() { }
+#endif
+};
+
 static const AtomicString& AudioKindToString(WebMediaPlayerClient::AudioTrackKind kind)
 {
     switch (kind) {
@@ -3393,17 +3417,10 @@ void HTMLMediaElement::clearMediaPlayer(int flags)
 
     cancelDeferredLoad();
 
-#if ENABLE(WEB_AUDIO)
-    if (m_audioSourceNode)
-        m_audioSourceNode->lock();
-#endif
-
-    clearMediaPlayerAndAudioSourceProviderClientWithoutLocking();
-
-#if ENABLE(WEB_AUDIO)
-    if (m_audioSourceNode)
-        m_audioSourceNode->unlock();
-#endif
+    {
+        AudioSourceProviderClientLockScope scope(*this);
+        clearMediaPlayerAndAudioSourceProviderClientWithoutLocking();
+    }
 
     stopPeriodicTimers();
     m_loadTimer.stop();
@@ -3688,22 +3705,16 @@ void* HTMLMediaElement::preDispatchEventHandler(Event* event)
 
 void HTMLMediaElement::createMediaPlayer()
 {
-#if ENABLE(WEB_AUDIO)
-    if (m_audioSourceNode)
-        m_audioSourceNode->lock();
-#endif
+    AudioSourceProviderClientLockScope scope(*this);
 
     closeMediaSource();
 
     m_player = MediaPlayer::create(this);
 
 #if ENABLE(WEB_AUDIO)
-    if (m_audioSourceNode) {
+    if (m_audioSourceNode && audioSourceProvider()) {
         // When creating the player, make sure its AudioSourceProvider knows about the client.
-        if (audioSourceProvider())
-            audioSourceProvider()->setClient(m_audioSourceNode);
-
-        m_audioSourceNode->unlock();
+        audioSourceProvider()->setClient(m_audioSourceNode);
     }
 #endif
 }
@@ -3713,14 +3724,9 @@ void HTMLMediaElement::setAudioSourceNode(AudioSourceProviderClient* sourceNode)
 {
     m_audioSourceNode = sourceNode;
 
-    if (m_audioSourceNode)
-        m_audioSourceNode->lock();
-
+    AudioSourceProviderClientLockScope scope(*this);
     if (audioSourceProvider())
         audioSourceProvider()->setClient(m_audioSourceNode);
-
-    if (m_audioSourceNode)
-        m_audioSourceNode->unlock();
 }
 
 AudioSourceProvider* HTMLMediaElement::audioSourceProvider()