Oilpan: Don't destruct HRTFDatabaseLoader::m_thread during a sweeping phase

It is not allowed to destruct HRTFDatabaseLoader::m_thread during a sweeping phase
because WebThreadSupportingGC's destructor enters a safe point scope.
This CL avoids the situation by explicitly joining with the loader thread in AudioContext::uninitialize().

In order to make sure that the loader thread finishes touching m_thread,
this CL posts a clean-up task and wait for its completion before calling
m_thread.clear().

BUG=432041

Review URL: https://codereview.chromium.org/711323002

git-svn-id: svn://svn.chromium.org/blink/trunk@185177 bbb929c8-8fbe-4397-9dbb-9b2b20218538

third_party/WebKit/Source/modules/webaudio/AudioContext.cpp

@@ -201,6 +201,9 @@ void AudioContext::uninitialize()
     // Get rid of the sources which may still be playing.
     derefUnfinishedSourceNodes();
 
+    ASSERT(m_listener);
+    m_listener->waitForHRTFDatabaseLoaderThreadCompletion();
+
     clear();
 }
 

third_party/WebKit/Source/modules/webaudio/AudioListener.cpp

@@ -92,7 +92,8 @@ bool AudioListener::isHRTFDatabaseLoaded()
 
 void AudioListener::waitForHRTFDatabaseLoaderThreadCompletion()
 {
-    m_hrtfDatabaseLoader->waitForLoaderThreadCompletion();
+    if (m_hrtfDatabaseLoader)
+        m_hrtfDatabaseLoader->waitForLoaderThreadCompletion();
 }
 
 void AudioListener::markPannersAsDirty(unsigned type)

third_party/WebKit/Source/platform/audio/HRTFDatabaseLoader.cpp

@@ -33,6 +33,7 @@
 #include "platform/audio/HRTFDatabaseLoader.h"
 
 #include "platform/Task.h"
+#include "platform/TaskSynchronizer.h"
 #include "public/platform/Platform.h"
 #include "wtf/MainThread.h"
 
@@ -71,10 +72,10 @@ HRTFDatabaseLoader::HRTFDatabaseLoader(float sampleRate)
 HRTFDatabaseLoader::~HRTFDatabaseLoader()
 {
     ASSERT(isMainThread());
-    waitForLoaderThreadCompletion();
+    ASSERT(!m_thread);
 }
 
-void HRTFDatabaseLoader::load()
+void HRTFDatabaseLoader::loadTask()
 {
     ASSERT(!isMainThread());
     m_thread->attachGC();
@@ -98,7 +99,7 @@ void HRTFDatabaseLoader::loadAsynchronously()
     if (!m_hrtfDatabase && !m_thread) {
         // Start the asynchronous database loading process.
         m_thread = WebThreadSupportingGC::create("HRTF database loader");
-        m_thread->postTask(new Task(WTF::bind(&HRTFDatabaseLoader::load, this)));
+        m_thread->postTask(new Task(WTF::bind(&HRTFDatabaseLoader::loadTask, this)));
     }
 }
 
@@ -108,8 +109,21 @@ bool HRTFDatabaseLoader::isLoaded()
     return m_hrtfDatabase;
 }
 
+// This cleanup task is needed just to make sure that the loader thread finishes
+// the load task and thus the loader thread doesn't touch m_thread any more.
+void HRTFDatabaseLoader::cleanupTask(TaskSynchronizer* sync)
+{
+    sync->taskCompleted();
+}
+
 void HRTFDatabaseLoader::waitForLoaderThreadCompletion()
 {
+    if (!m_thread)
+        return;
+
+    TaskSynchronizer sync;
+    m_thread->postTask(new Task(WTF::bind(&HRTFDatabaseLoader::cleanupTask, this, &sync)));
+    sync.waitForTaskCompletion();
     m_thread.clear();
 }
 

third_party/WebKit/Source/platform/audio/HRTFDatabaseLoader.h

@@ -37,6 +37,8 @@
 
 namespace blink {
 
+class TaskSynchronizer;
+
 // HRTFDatabaseLoader will asynchronously load the default HRTFDatabase in a new thread.
 
 class PLATFORM_EXPORT HRTFDatabaseLoader final : public GarbageCollectedFinalized<HRTFDatabaseLoader> {
@@ -60,9 +62,6 @@ public:
 
     float databaseSampleRate() const { return m_databaseSampleRate; }
 
-    // Called in asynchronous loading thread.
-    void load();
-
     void trace(Visitor*) { }
 
 private:
@@ -73,6 +72,10 @@ private:
     // This must be called from the main thread.
     void loadAsynchronously();
 
+    // Called in asynchronous loading thread.
+    void loadTask();
+    void cleanupTask(TaskSynchronizer*);
+
     // Holding a m_lock is required when accessing m_hrtfDatabase since we access it from multiple threads.
     Mutex m_lock;
     OwnPtr<HRTFDatabase> m_hrtfDatabase;