Oilpan: We need to collect all garbage before shutting down the worker thread

Source/core/workers/WorkerThread.cpp

Index: Source/core/workers/WorkerThread.cpp
diff --git a/Source/core/workers/WorkerThread.cpp b/Source/core/workers/WorkerThread.cpp
index 7d6efc7e0b26cba91178b60b26e619b6bdb76e67..f71b83f90056f4710749a84ef343b99e1114581a 100644
--- a/Source/core/workers/WorkerThread.cpp
+++ b/Source/core/workers/WorkerThread.cpp
@@ -137,23 +137,25 @@ void WorkerThread::workerThread()
 
     ThreadIdentifier threadID = m_threadID;
 
+    // We need to collect all garbage before checking that the WorkerThread has the last reference
+    // to the WorkerGlobalScope. We don't need to call V8's GC because all wrappers of the worker thread
+    // are stored in DOMWrapperMap (i.e., no wrappers of the worker thread are stored in ScriptWrappable)
+    // and they are already cleared out in ~WorkerScriptController(). In short, we just need to call
+    // oilpan's GC to collect all garbage.
+    Heap::collectAllGarbage(ThreadState::NoHeapPointersOnStack);

[haraken, 2014/03/05 05:08:35]

Actually, I'll remove this code soon because the following ASSERT will be
removed by sof's CL that moves WorkerGlobalScope to the heap.

After removing the ASSERT, we just need to make sure that the thread heap is
empty at the end of ThreadState::cleanup(). In other words, we just need to make
sure that all garbage is collected before checking that the thread heap is
empty. However, this is already done in ThreadState::cleanup().

In conclusion, once we remove the ASSERT, we can just remove
Heap::collectAllGarbage().

[Mads Ager (chromium), 2014/03/05 07:40:34]

We should just #ifdef out the ASSERT now so we don't have to introduce the
comment above. Then either you or sof will merge that. :-)

[haraken, 2014/03/05 08:50:26]

Done.

     ASSERT(m_workerGlobalScope->hasOneRef());
 
     // The below assignment will destroy the context, which will in turn notify messaging proxy.
     // We cannot let any objects survive past thread exit, because no other thread will run GC or otherwise destroy them.
     m_workerGlobalScope = nullptr;
 
-    // Cleanup thread heap which causes all objects to be finalized.
-    // After this call thread heap must be empty.
-    ThreadState::current()->cleanup();
+    ThreadState::detach();
 
     // Clean up PlatformThreadData before WTF::WTFThreadData goes away!
     PlatformThreadData::current().destroy();
 
     // The thread object may be already destroyed from notification now, don't try to access "this".
     detachThread(threadID);
-
-    ThreadState::detach();
 }
 
 void WorkerThread::runEventLoop()