bytecode/ArrayAllocationProfile.cpp

   1 /*
   2  * Copyright (C) 2012, 2013 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. ``AS IS'' AND ANY
  14  * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  15  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
  16  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
  17  * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
  18  * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
  19  * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
  20  * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
  21  * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  22  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  23  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  24  */
  25
  26 #include "config.h"
  27 #include "ArrayAllocationProfile.h"
  28
  29 #include "JSCInlines.h"
  30
  31 namespace JSC {
  32
  33 void ArrayAllocationProfile::updateIndexingType()
  34 {
  35     // This is awkwardly racy but totally sound even when executed concurrently. The
  36     // worst cases go something like this:
  37     //
  38     // - Two threads race to execute this code; one of them succeeds in updating the
  39     //   m_currentIndexingType and the other either updates it again, or sees a null
  40     //   m_lastArray; if it updates it again then at worst it will cause the profile
  41     //   to "forget" some array. That's still sound, since we don't promise that
  42     //   this profile is a reflection of any kind of truth.
  43     //
  44     // - A concurrent thread reads m_lastArray, but that array is now dead. While
  45     //   it's possible for that array to no longer be reachable, it cannot actually
  46     //   be freed, since we require the GC to wait until all concurrent JITing
  47     //   finishes.
  48
  49     JSArray* lastArray = m_lastArray;
  50     if (!lastArray)
  51         return;
  52     m_currentIndexingType = leastUpperBoundOfIndexingTypes(m_currentIndexingType, lastArray->indexingType());
  53     m_lastArray = 0;
  54 }
  55
  56 } // namespace JSC
  57