compositor-worker: Keep worker backing thread alive for the lifetime of the compositor thread.

third_party/WebKit/Source/core/workers/WorkerBackingThread.cpp

Index: third_party/WebKit/Source/core/workers/WorkerBackingThread.cpp
diff --git a/third_party/WebKit/Source/core/workers/WorkerBackingThread.cpp b/third_party/WebKit/Source/core/workers/WorkerBackingThread.cpp
index 040ce92ea79208362ca3f48cfceb67291d092614..1d400490bf6e991094c6e735012ce0a86638f432 100644
--- a/third_party/WebKit/Source/core/workers/WorkerBackingThread.cpp
+++ b/third_party/WebKit/Source/core/workers/WorkerBackingThread.cpp
@@ -11,6 +11,7 @@
 #include "bindings/core/v8/V8PerIsolateData.h"
 #include "platform/RuntimeEnabledFeatures.h"
 #include "platform/ThreadSafeFunctional.h"
+#include "platform/WaitableEvent.h"
 #include "platform/WebThreadSupportingGC.h"
 #include "public/platform/Platform.h"
 #include "public/platform/WebTraceLocation.h"
@@ -29,10 +30,15 @@ WorkerBackingThread::WorkerBackingThread(WebThread* thread, bool shouldCallGCOnS
     , m_isOwningThread(false)
     , m_shouldCallGCOnShutdown(shouldCallGCOnShutdown)
 {
+    // WorkerBackingThread is created on main but needs to be initialized on the
+    // thread in order to attach that thread.
+    thread->getWebTaskRunner()->postTask(BLINK_FROM_HERE, threadSafeBind(&WorkerBackingThread::initialize, AllowCrossThreadAccess(this)));

[haraken, 2016/05/11 00:18:31]

I still don't understand why you have to call initialize() here. attach() also
calls initialize(). Don't we end up with calling initialize() twice?

[flackr, 2016/05/18 05:26:50]

I've changed WorkerBackingThread so that when you wrap an existing thread it
initializes once and does nothing when attach / detach are called and doesn't
call shutdown until you destruct the WorkerBackingThread. This is because we
can't call ThreadState::detach until we no longer have any oilpan objects owned
by the compositor thread.

 }
 
 WorkerBackingThread::~WorkerBackingThread()
 {
+    if (!m_isOwningThread)
+        signalShutdownAndWait();

[haraken, 2016/05/11 00:18:31]

I'd move this to CompositorWorkerThread::clearSharedBackingThread (since it's
not a good idea to do complicated stuff in a destructor).

[flackr, 2016/05/18 05:26:50]

Done.

 #if DCHECK_IS_ON()
     MutexLocker locker(m_mutex);
     DCHECK_EQ(0u, m_workerScriptCount);
@@ -46,7 +52,8 @@ void WorkerBackingThread::attach()
         if (++m_workerScriptCount > 1)
             return;
     }
-    initialize();
+    if (m_isOwningThread)
+        initialize();
 }
 
 void WorkerBackingThread::detach()
@@ -56,7 +63,8 @@ void WorkerBackingThread::detach()
         if (--m_workerScriptCount > 0)
             return;
     }
-    shutdown();
+    if (m_isOwningThread)
+        shutdown();
 }
 
 void WorkerBackingThread::initialize()
@@ -75,7 +83,7 @@ void WorkerBackingThread::initialize()
         Platform::current()->didStartWorkerThread();
 }
 
-void WorkerBackingThread::shutdown()
+void WorkerBackingThread::shutdown(WaitableEvent* doneEvent)
 {
     if (m_isOwningThread)
         Platform::current()->willStopWorkerThread();
@@ -90,6 +98,15 @@ void WorkerBackingThread::shutdown()
 
     V8PerIsolateData::destroy(m_isolate);
     m_isolate = nullptr;
+    if (doneEvent)
+        doneEvent->signal();
+}
+
+void WorkerBackingThread::signalShutdownAndWait()
+{
+    WaitableEvent doneEvent;
+    m_backingThread->platformThread().getWebTaskRunner()->postTask(BLINK_FROM_HERE, threadSafeBind(&WorkerBackingThread::shutdown, AllowCrossThreadAccess(this), AllowCrossThreadAccess(&doneEvent)));
+    doneEvent.wait();
 }
 
 } // namespace blink