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/*
* Copyright (C) 2016-2021 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(JSC::Heap& heap)
: m_heap(heap)
{
m_heap.releaseAccess();
}
~ReleaseHeapAccessScope()
{
m_heap.acquireAccess();
}
private:
JSC::Heap& m_heap;
};
class ReleaseHeapAccessIfNeededScope {
public:
ReleaseHeapAccessIfNeededScope(JSC::Heap& heap)
: m_heap(heap)
{
hadHeapAccess = m_heap.hasAccess();
if (hadHeapAccess)
m_heap.releaseAccess();
}
~ReleaseHeapAccessIfNeededScope()
{
if (hadHeapAccess)
m_heap.acquireAccess();
}
private:
JSC::Heap& m_heap;
bool hadHeapAccess { false };
};
} // namespace JSC
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