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<dt>Revision</dt> <dd><a href="http://trac.webkit.org/projects/webkit/changeset/283685">283685</a></dd>
<dt>Author</dt> <dd>jya@apple.com</dd>
<dt>Date</dt> <dd>2021-10-06 17:43:09 -0700 (Wed, 06 Oct 2021)</dd>
</dl>

<h3>Log Message</h3>
<pre>Have SourceBufferPrivateAVJObjC use WorkQueue instead of dispatch_async
https://bugs.webkit.org/show_bug.cgi?id=230881
rdar://83429276

This change is twofold:
1- dispatch_async takes an objective-C block which doesn't support C++ move
semantics. As such the lambda would be copied including the captured variables.
When use with a non-thread safe refcounted object it could lead to a race
on the refcount which would result in a leak.
By using a WorkQueue instead, we avoid the above problem.
2- We want to unify in the media code how threads are created and task
dispatched: WorkQueue is a nice solution.

Reviewed by Chris Dumez.

No observable difference.

* platform/graphics/avfoundation/objc/SourceBufferPrivateAVFObjC.h:
* platform/graphics/avfoundation/objc/SourceBufferPrivateAVFObjC.mm:
(WebCore::SourceBufferPrivateAVFObjC::SourceBufferPrivateAVFObjC):
(WebCore::SourceBufferPrivateAVFObjC::append):
(WebCore::SourceBufferPrivateAVFObjC::resetParserState):</pre>

<h3>Modified Paths</h3>
<ul>
<li><a href="#trunkSourceWebCoreChangeLog">trunk/Source/WebCore/ChangeLog</a></li>
<li><a href="#trunkSourceWebCoreplatformgraphicsavfoundationobjcSourceBufferPrivateAVFObjCh">trunk/Source/WebCore/platform/graphics/avfoundation/objc/SourceBufferPrivateAVFObjC.h</a></li>
<li><a href="#trunkSourceWebCoreplatformgraphicsavfoundationobjcSourceBufferPrivateAVFObjCmm">trunk/Source/WebCore/platform/graphics/avfoundation/objc/SourceBufferPrivateAVFObjC.mm</a></li>
</ul>

</div>
<div id="patch">
<h3>Diff</h3>
<a id="trunkSourceWebCoreChangeLog"></a>
<div class="modfile"><h4>Modified: trunk/Source/WebCore/ChangeLog (283684 => 283685)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/WebCore/ChangeLog   2021-10-07 00:32:40 UTC (rev 283684)
+++ trunk/Source/WebCore/ChangeLog      2021-10-07 00:43:09 UTC (rev 283685)
</span><span class="lines">@@ -1,3 +1,28 @@
</span><ins>+2021-10-06  Jean-Yves Avenard  <jya@apple.com>
+
+        Have SourceBufferPrivateAVJObjC use WorkQueue instead of dispatch_async
+        https://bugs.webkit.org/show_bug.cgi?id=230881
+        rdar://83429276
+
+        This change is twofold:
+        1- dispatch_async takes an objective-C block which doesn't support C++ move
+        semantics. As such the lambda would be copied including the captured variables.
+        When use with a non-thread safe refcounted object it could lead to a race
+        on the refcount which would result in a leak.
+        By using a WorkQueue instead, we avoid the above problem.
+        2- We want to unify in the media code how threads are created and task
+        dispatched: WorkQueue is a nice solution.
+
+        Reviewed by Chris Dumez.
+
+        No observable difference.
+
+        * platform/graphics/avfoundation/objc/SourceBufferPrivateAVFObjC.h:
+        * platform/graphics/avfoundation/objc/SourceBufferPrivateAVFObjC.mm:
+        (WebCore::SourceBufferPrivateAVFObjC::SourceBufferPrivateAVFObjC):
+        (WebCore::SourceBufferPrivateAVFObjC::append):
+        (WebCore::SourceBufferPrivateAVFObjC::resetParserState):
+
</ins><span class="cx"> 2021-10-06  Tyler Wilcock  <tyler_w@apple.com>
</span><span class="cx"> 
</span><span class="cx">         AX: Make AccessibilityObjectInterface::contents return-by-value instead of return-by-out-parameter
</span></span></pre></div>
<a id="trunkSourceWebCoreplatformgraphicsavfoundationobjcSourceBufferPrivateAVFObjCh"></a>
<div class="modfile"><h4>Modified: trunk/Source/WebCore/platform/graphics/avfoundation/objc/SourceBufferPrivateAVFObjC.h (283684 => 283685)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/WebCore/platform/graphics/avfoundation/objc/SourceBufferPrivateAVFObjC.h    2021-10-07 00:32:40 UTC (rev 283684)
+++ trunk/Source/WebCore/platform/graphics/avfoundation/objc/SourceBufferPrivateAVFObjC.h       2021-10-07 00:43:09 UTC (rev 283685)
</span><span class="lines">@@ -56,6 +56,10 @@
</span><span class="cx"> typedef struct opaqueCMSampleBuffer *CMSampleBufferRef;
</span><span class="cx"> typedef const struct opaqueCMFormatDescription *CMFormatDescriptionRef;
</span><span class="cx"> 
</span><ins>+namespace WTF {
+class WorkQueue;
+}
+
</ins><span class="cx"> namespace WebCore {
</span><span class="cx"> 
</span><span class="cx"> class CDMInstance;
</span><span class="lines">@@ -206,7 +210,7 @@
</span><span class="cx">     RetainPtr<NSError> m_hdcpError;
</span><span class="cx">     Box<BinarySemaphore> m_hasSessionSemaphore;
</span><span class="cx">     Box<Semaphore> m_abortSemaphore;
</span><del>-    OSObjectPtr<dispatch_group_t> m_isAppendingGroup;
</del><ins>+    const Ref<WTF::WorkQueue> m_appendQueue;
</ins><span class="cx">     RefPtr<WebCoreDecompressionSession> m_decompressionSession;
</span><span class="cx"> 
</span><span class="cx">     MediaSourcePrivateAVFObjC* m_mediaSource;
</span></span></pre></div>
<a id="trunkSourceWebCoreplatformgraphicsavfoundationobjcSourceBufferPrivateAVFObjCmm"></a>
<div class="modfile"><h4>Modified: trunk/Source/WebCore/platform/graphics/avfoundation/objc/SourceBufferPrivateAVFObjC.mm (283684 => 283685)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/WebCore/platform/graphics/avfoundation/objc/SourceBufferPrivateAVFObjC.mm   2021-10-07 00:32:40 UTC (rev 283684)
+++ trunk/Source/WebCore/platform/graphics/avfoundation/objc/SourceBufferPrivateAVFObjC.mm      2021-10-07 00:43:09 UTC (rev 283685)
</span><span class="lines">@@ -60,6 +60,7 @@
</span><span class="cx"> #import <wtf/SoftLinking.h>
</span><span class="cx"> #import <wtf/WTFSemaphore.h>
</span><span class="cx"> #import <wtf/WeakPtr.h>
</span><ins>+#import <wtf/WorkQueue.h>
</ins><span class="cx"> #import <wtf/text/AtomString.h>
</span><span class="cx"> #import <wtf/text/CString.h>
</span><span class="cx"> #import <wtf/text/StringToIntegerConversion.h>
</span><span class="lines">@@ -304,7 +305,7 @@
</span><span class="cx"> SourceBufferPrivateAVFObjC::SourceBufferPrivateAVFObjC(MediaSourcePrivateAVFObjC* parent, Ref<SourceBufferParser>&& parser)
</span><span class="cx">     : m_parser(WTFMove(parser))
</span><span class="cx">     , m_errorListener(adoptNS([[WebAVSampleBufferErrorListener alloc] initWithParent:makeWeakPtr(*this)]))
</span><del>-    , m_isAppendingGroup(adoptOSObject(dispatch_group_create()))
</del><ins>+    , m_appendQueue(WorkQueue::create("SourceBufferPrivateAVFObjC data parser queue"))
</ins><span class="cx">     , m_mediaSource(parent)
</span><span class="cx">     , m_mapID(nextMapID())
</span><span class="cx"> #if !RELEASE_LOG_DISABLED
</span><span class="lines">@@ -562,16 +563,6 @@
</span><span class="cx">     UNUSED_PARAM(hasSessionSemaphore);
</span><span class="cx"> }
</span><span class="cx"> 
</span><del>-static dispatch_queue_t globalDataParserQueue()
-{
-    static dispatch_queue_t globalQueue;
-    static dispatch_once_t onceToken;
-    dispatch_once(&onceToken, ^{
-        globalQueue = dispatch_queue_create("SourceBufferPrivateAVFObjC data parser queue", DISPATCH_QUEUE_CONCURRENT);
-    });
-    return globalQueue;
-}
-
</del><span class="cx"> void SourceBufferPrivateAVFObjC::append(Ref<SharedBuffer>&& data)
</span><span class="cx"> {
</span><span class="cx">     ALWAYS_LOG(LOGIDENTIFIER, "data length = ", data->size());
</span><span class="lines">@@ -646,9 +637,8 @@
</span><span class="cx">     });
</span><span class="cx"> 
</span><span class="cx">     m_parsingSucceeded = true;
</span><del>-    dispatch_group_enter(m_isAppendingGroup.get());
</del><span class="cx"> 
</span><del>-    dispatch_async(globalDataParserQueue(), [data = WTFMove(data), weakThis = m_appendWeakFactory.createWeakPtr(*this), parser = m_parser, isAppendingGroup = m_isAppendingGroup, abortCalled = m_abortCalled]() mutable {
</del><ins>+    m_appendQueue->dispatch([data = WTFMove(data), weakThis = m_appendWeakFactory.createWeakPtr(*this), parser = m_parser, abortCalled = m_abortCalled]() mutable {
</ins><span class="cx">         parser->appendData(WTFMove(data), [weakThis = WTFMove(weakThis), abortCalled]() mutable {
</span><span class="cx">             callOnMainThread([weakThis = WTFMove(weakThis), abortCalled] {
</span><span class="cx">                 if (!weakThis || abortCalled != weakThis->m_abortCalled)
</span><span class="lines">@@ -662,7 +652,6 @@
</span><span class="cx">                 weakThis->appendCompleted();
</span><span class="cx">             });
</span><span class="cx">         });
</span><del>-        dispatch_group_leave(isAppendingGroup.get());
</del><span class="cx">     });
</span><span class="cx"> }
</span><span class="cx"> 
</span><span class="lines">@@ -708,7 +697,8 @@
</span><span class="cx"> {
</span><span class="cx">     ALWAYS_LOG(LOGIDENTIFIER);
</span><span class="cx"> 
</span><del>-    dispatch_group_wait(m_isAppendingGroup.get(), DISPATCH_TIME_FOREVER);
</del><ins>+    // Wait until all tasks in the workqueue have run.
+    m_appendQueue->dispatchSync([] { });
</ins><span class="cx">     m_mediaSamples.clear();
</span><span class="cx">     m_hasPendingAppendCompletedCallback = false;
</span><span class="cx">     m_processingInitializationSegment = false;
</span></span></pre>
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