Finish completeSweep before shutting down V8

third_party/WebKit/Source/platform/heap/ThreadState.cpp

Index: third_party/WebKit/Source/platform/heap/ThreadState.cpp
diff --git a/third_party/WebKit/Source/platform/heap/ThreadState.cpp b/third_party/WebKit/Source/platform/heap/ThreadState.cpp
index 8446223a5880b38e074f72b38ad995b6393ba25a..ba16cfa8dd16132f2c475d397aaf4f52a59208fb 100644
--- a/third_party/WebKit/Source/platform/heap/ThreadState.cpp
+++ b/third_party/WebKit/Source/platform/heap/ThreadState.cpp
@@ -209,6 +209,16 @@ void ThreadState::attachMainThread()
     attachedThreads().add(state);
 }
 
+
+void ThreadState::stopMainThread()
+{
+    ASSERT(isMainThread());
+
+    // Finish sweeping before shutting down V8. Otherwise, some destructor
+    // may access V8 and cause crashes.
+    completeSweep();

[haraken, 2016/03/10 05:42:23]

Maybe we should add enterGCForbidenScope() before finishing stopMainThread() to
make sure that no GC happens before detaching the main thread. (I don't have a
strong opinion.)

[haraken, 2016/03/10 05:42:23]

Another option is just to remove completeSweep(). There is no reason we have to
complete sweeping before shutting down the main thread. However, I prefer
completing sweeping just in case.

In production, blink::shutdown would rarely be called because the renderer is
killed immediately in common cases. So having completeSweep() in the shutdown
sequence won't matter for real-world performance.

+}
+
 void ThreadState::detachMainThread()
 {
     // Enter a safe point before trying to acquire threadAttachMutex
@@ -221,20 +231,17 @@ void ThreadState::detachMainThread()
     // You must call unregisterTraceDOMWrappers before detaching
     // the main thread.
     ASSERT(!state->m_isolate);
+    ASSERT(!state->isSweepingInProgress());
 
-    // 1. Finish sweeping.
-    state->completeSweep();
-    {
-        SafePointAwareMutexLocker locker(threadAttachMutex(), BlinkGC::NoHeapPointersOnStack);
+    SafePointAwareMutexLocker locker(threadAttachMutex(), BlinkGC::NoHeapPointersOnStack);
 
-        // 2. Add the main thread's heap pages to the orphaned pool.
-        state->cleanupPages();
+    // Add the main thread's heap pages to the orphaned pool.
+    state->cleanupPages();
 
-        // 3. Detach the main thread.
-        ASSERT(attachedThreads().contains(state));
-        attachedThreads().remove(state);
-        state->~ThreadState();
-    }
+    // Detach the main thread.
+    ASSERT(attachedThreads().contains(state));
+    attachedThreads().remove(state);
+    state->~ThreadState();
 }
 
 void ThreadState::attach()