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diff --git a/Source/JavaScriptCore/heap/ReleaseHeapAccessScope.h b/Source/JavaScriptCore/heap/ReleaseHeapAccessScope.h
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+++ b/Source/JavaScriptCore/heap/ReleaseHeapAccessScope.h
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+/*
+ * Copyright (C) 2016 Apple Inc. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS''
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
+ * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+ * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
+ * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
+ * THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include "Heap.h"
+
+namespace JSC {
+
+// Almost all of the VM's code runs with "heap access". This means that the GC thread believes that
+// the VM is messing with the heap in a way that would be unsafe for certain phases of the collector,
+// like the weak reference fixpoint, stack scanning, and changing barrier modes. However, many long
+// running operations inside the VM don't require heap access. For example, memcpying a typed array
+// if a reference to it is on the stack is totally fine without heap access. Blocking on a futex is
+// also fine without heap access. Releasing heap access for long-running code (in the case of futex
+// wait, possibly infinitely long-running) ensures that the GC can finish a collection cycle while
+// you are waiting.
+class ReleaseHeapAccessScope {
+public:
+    ReleaseHeapAccessScope(Heap& heap)
+        : m_heap(heap)
+    {
+        m_heap.releaseAccess();
+    }
+    
+    ~ReleaseHeapAccessScope()
+    {
+        m_heap.acquireAccess();
+    }
+
+private:
+    Heap& m_heap;
+};
+
+} // namespace JSC
+