heap/BlockAllocator.cpp

   1 /*
   2  * Copyright (C) 2012 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 #include "config.h"
  27 #include "BlockAllocator.h"
  28
  29 #include "MarkedBlock.h"
  30 #include <wtf/CurrentTime.h>
  31
  32 namespace JSC {
  33
  34 BlockAllocator::BlockAllocator()
  35     : m_numberOfFreeBlocks(0)
  36     , m_isCurrentlyAllocating(false)
  37     , m_blockFreeingThreadShouldQuit(false)
  38     , m_blockFreeingThread(GCActivityCallback::s_shouldCreateGCTimer ?
  39         createThread(blockFreeingThreadStartFunc, this, "JavaScriptCore::BlockFree") : 0)
  40 {
  41     ASSERT(m_blockFreeingThread || !GCActivityCallback::s_shouldCreateGCTimer);
  42 }
  43
  44 BlockAllocator::~BlockAllocator()
  45 {
  46     releaseFreeBlocks();
  47     {
  48         MutexLocker locker(m_freeBlockLock);
  49         m_blockFreeingThreadShouldQuit = true;
  50         m_freeBlockCondition.broadcast();
  51     }
  52     if (GCActivityCallback::s_shouldCreateGCTimer)
  53         waitForThreadCompletion(m_blockFreeingThread);
  54 }
  55
  56 void BlockAllocator::releaseFreeBlocks()
  57 {
  58     while (true) {
  59         MarkedBlock* block;
  60         {
  61             MutexLocker locker(m_freeBlockLock);
  62             if (!m_numberOfFreeBlocks)
  63                 block = 0;
  64             else {
  65                 // FIXME: How do we know this is a MarkedBlock? It could be a CopiedBlock.
  66                 block = static_cast<MarkedBlock*>(m_freeBlocks.removeHead());
  67                 ASSERT(block);
  68                 m_numberOfFreeBlocks--;
  69             }
  70         }
  71
  72         if (!block)
  73             break;
  74
  75         MarkedBlock::destroy(block);
  76     }
  77 }
  78
  79 void BlockAllocator::waitForRelativeTimeWhileHoldingLock(double relative)
  80 {
  81     if (m_blockFreeingThreadShouldQuit)
  82         return;
  83     m_freeBlockCondition.timedWait(m_freeBlockLock, currentTime() + relative);
  84 }
  85
  86 void BlockAllocator::waitForRelativeTime(double relative)
  87 {
  88     // If this returns early, that's fine, so long as it doesn't do it too
  89     // frequently. It would only be a bug if this function failed to return
  90     // when it was asked to do so.
  91
  92     MutexLocker locker(m_freeBlockLock);
  93     waitForRelativeTimeWhileHoldingLock(relative);
  94 }
  95
  96 void BlockAllocator::blockFreeingThreadStartFunc(void* blockAllocator)
  97 {
  98     static_cast<BlockAllocator*>(blockAllocator)->blockFreeingThreadMain();
  99 }
 100
 101 void BlockAllocator::blockFreeingThreadMain()
 102 {
 103     while (!m_blockFreeingThreadShouldQuit) {
 104         // Generally wait for one second before scavenging free blocks. This
 105         // may return early, particularly when we're being asked to quit.
 106         waitForRelativeTime(1.0);
 107         if (m_blockFreeingThreadShouldQuit)
 108             break;
 109
 110         if (m_isCurrentlyAllocating) {
 111             m_isCurrentlyAllocating = false;
 112             continue;
 113         }
 114
 115         // Now process the list of free blocks. Keep freeing until half of the
 116         // blocks that are currently on the list are gone. Assume that a size_t
 117         // field can be accessed atomically.
 118         size_t currentNumberOfFreeBlocks = m_numberOfFreeBlocks;
 119         if (!currentNumberOfFreeBlocks)
 120             continue;
 121
 122         size_t desiredNumberOfFreeBlocks = currentNumberOfFreeBlocks / 2;
 123
 124         while (!m_blockFreeingThreadShouldQuit) {
 125             MarkedBlock* block;
 126             {
 127                 MutexLocker locker(m_freeBlockLock);
 128                 if (m_numberOfFreeBlocks <= desiredNumberOfFreeBlocks)
 129                     block = 0;
 130                 else {
 131                     // FIXME: How do we know this is a MarkedBlock? It could be a CopiedBlock.
 132                     block = static_cast<MarkedBlock*>(m_freeBlocks.removeHead());
 133                     ASSERT(block);
 134                     m_numberOfFreeBlocks--;
 135                 }
 136             }
 137
 138             if (!block)
 139                 break;
 140
 141             MarkedBlock::destroy(block);
 142         }
 143     }
 144 }
 145
 146 } // namespace JSC