heap/BlockAllocator.h

   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 #ifndef BlockAllocator_h
  27 #define BlockAllocator_h
  28
  29 #include "GCActivityCallback.h"
  30 #include <wtf/DoublyLinkedList.h>
  31 #include <wtf/Forward.h>
  32 #include <wtf/Threading.h>
  33
  34 namespace JSC {
  35
  36 class HeapBlock;
  37
  38 // Simple allocator to reduce VM cost by holding onto blocks of memory for
  39 // short periods of time and then freeing them on a secondary thread.
  40
  41 class BlockAllocator {
  42 public:
  43     BlockAllocator();
  44     ~BlockAllocator();
  45
  46     HeapBlock* allocate();
  47     void deallocate(HeapBlock*);
  48
  49 private:
  50     void waitForRelativeTimeWhileHoldingLock(double relative);
  51     void waitForRelativeTime(double relative);
  52
  53     void blockFreeingThreadMain();
  54     static void blockFreeingThreadStartFunc(void* heap);
  55
  56     void releaseFreeBlocks();
  57
  58     DoublyLinkedList<HeapBlock> m_freeBlocks;
  59     size_t m_numberOfFreeBlocks;
  60     bool m_isCurrentlyAllocating;
  61     bool m_blockFreeingThreadShouldQuit;
  62     Mutex m_freeBlockLock;
  63     ThreadCondition m_freeBlockCondition;
  64     ThreadIdentifier m_blockFreeingThread;
  65 };
  66
  67 inline HeapBlock* BlockAllocator::allocate()
  68 {
  69     MutexLocker locker(m_freeBlockLock);
  70     m_isCurrentlyAllocating = true;
  71     if (!m_numberOfFreeBlocks) {
  72         ASSERT(m_freeBlocks.isEmpty());
  73         return 0;
  74     }
  75
  76     ASSERT(!m_freeBlocks.isEmpty());
  77     m_numberOfFreeBlocks--;
  78     return m_freeBlocks.removeHead();
  79 }
  80
  81 inline void BlockAllocator::deallocate(HeapBlock* block)
  82 {
  83     {
  84         MutexLocker locker(m_freeBlockLock);
  85         m_freeBlocks.push(block);
  86         m_numberOfFreeBlocks++;
  87     }
  88     if (!GCActivityCallback::s_shouldCreateGCTimer);
  89         releaseFreeBlocks();
  90 }
  91
  92 } // namespace JSC
  93
  94 #endif // BlockAllocator_h