1/*
2 * Copyright (C) 2016 Apple Inc. All rights reserved.
3 *
4 * Redistribution and use in source and binary forms, with or without
5 * modification, are permitted provided that the following conditions
6 * are met:
7 * 1. Redistributions of source code must retain the above copyright
8 * notice, this list of conditions and the following disclaimer.
9 * 2. Redistributions in binary form must reproduce the above copyright
10 * notice, this list of conditions and the following disclaimer in the
11 * documentation and/or other materials provided with the distribution.
12 *
13 * THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS''
14 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
15 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
16 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
17 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
18 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
19 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
20 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
21 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
22 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
23 * THE POSSIBILITY OF SUCH DAMAGE.
24 */
25
26#pragma once
27
28#include "Heap.h"
29
30namespace JSC {
31
32// Almost all of the VM's code runs with "heap access". This means that the GC thread believes that
33// the VM is messing with the heap in a way that would be unsafe for certain phases of the collector,
34// like the weak reference fixpoint, stack scanning, and changing barrier modes. However, many long
35// running operations inside the VM don't require heap access. For example, memcpying a typed array
36// if a reference to it is on the stack is totally fine without heap access. Blocking on a futex is
37// also fine without heap access. Releasing heap access for long-running code (in the case of futex
38// wait, possibly infinitely long-running) ensures that the GC can finish a collection cycle while
39// you are waiting.
40class ReleaseHeapAccessScope {
41public:
42 ReleaseHeapAccessScope(Heap& heap)
43 : m_heap(heap)
44 {
45 m_heap.releaseAccess();
46 }
47
48 ~ReleaseHeapAccessScope()
49 {
50 m_heap.acquireAccess();
51 }
52
53private:
54 Heap& m_heap;
55};
56
57} // namespace JSC
58
59