ArrayAllocationProfile.cpp 2.48 KB
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/*
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 * Copyright (C) 2012, 2013 Apple Inc. All rights reserved.
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 *
 * 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"

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#include "Operations.h"

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namespace JSC {

void ArrayAllocationProfile::updateIndexingType()
{
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    // 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.
    
    JSArray* lastArray = m_lastArray;
    if (!lastArray)
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        return;
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    m_currentIndexingType = leastUpperBoundOfIndexingTypes(m_currentIndexingType, lastArray->structure()->indexingType());
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    m_lastArray = 0;
}

} // namespace JSC