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/*
* Copyright (C) 2012, 2013 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. ``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
* 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.
*/
#include "config.h"
#include "ArrayAllocationProfile.h"
#include "JSCellInlines.h"
#include <algorithm>
namespace JSC {
void ArrayAllocationProfile::updateProfile()
{
// This is awkwardly racy but totally sound even when executed concurrently. The
// worst cases go something like this:
//
// - Two threads race to execute this code; one of them succeeds in updating the
// m_currentIndexingType and the other either updates it again, or sees a null
// m_lastArray; if it updates it again then at worst it will cause the profile
// to "forget" some array. That's still sound, since we don't promise that
// this profile is a reflection of any kind of truth.
//
// - A concurrent thread reads m_lastArray, but that array is now dead. While
// it's possible for that array to no longer be reachable, it cannot actually
// be freed, since we require the GC to wait until all concurrent JITing
// finishes.
//
// But one exception is vector length. We access vector length to get the vector
// length hint. However vector length can be accessible only from the main
// thread because large butterfly can be realloced in the main thread.
// So for now, we update the allocation profile only from the main thread.
ASSERT(!isCompilationThread());
Storage storage = std::exchange(m_storage, Storage(nullptr, m_storage.type()));
JSArray* lastArray = storage.pointer();
IndexingTypeAndVectorLength current = storage.type();
if (!lastArray)
return;
if (LIKELY(Options::useArrayAllocationProfiling())) {
// The basic model here is that we will upgrade ourselves to whatever the CoW version of lastArray is except ArrayStorage since we don't have CoW ArrayStorage.
IndexingType indexingType = leastUpperBoundOfIndexingTypes(current.indexingType() & IndexingTypeMask, lastArray->indexingType());
if (isCopyOnWrite(current.indexingType())) {
if (indexingType > ArrayWithContiguous)
indexingType = ArrayWithContiguous;
indexingType |= CopyOnWrite;
}
unsigned largestSeenVectorLength = std::min(std::max(current.vectorLength(), lastArray->getVectorLength()), BASE_CONTIGUOUS_VECTOR_LEN_MAX);
m_storage.setType(IndexingTypeAndVectorLength(indexingType, largestSeenVectorLength));
}
}
} // namespace JSC
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