wtf/BlockStack.h

   1 /*
   2  * Copyright (C) 2011 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 BlockStack_h
  27 #define BlockStack_h
  28
  29 #include <wtf/Assertions.h>
  30 #include <wtf/Vector.h>
  31
  32 namespace WTF {
  33
  34 template <typename T> class BlockStack {
  35 public:
  36     static const size_t blockSize = 4096;
  37     static const size_t blockLength = blockSize / sizeof(T);
  38
  39     BlockStack();
  40     ~BlockStack();
  41
  42     T* grow();
  43     void shrink(T*);
  44
  45     const Vector<T*>& blocks();
  46
  47 private:
  48     Vector<T*> m_blocks;
  49     T* m_spareBlock; // Used to avoid thrash at block boundaries.
  50 };
  51
  52 template <typename T> BlockStack<T>::BlockStack()
  53     : m_spareBlock(0)
  54 {
  55 }
  56
  57 template <typename T> BlockStack<T>::~BlockStack()
  58 {
  59     if (m_spareBlock)
  60         free(m_spareBlock);
  61     for (size_t i = 0; i < m_blocks.size(); ++i)
  62         free(m_blocks[i]);
  63 }
  64
  65 template <typename T> inline const Vector<T*>& BlockStack<T>::blocks()
  66 {
  67     return m_blocks;
  68 }
  69
  70 template <typename T> T* BlockStack<T>::grow()
  71 {
  72     T* block = m_spareBlock ? m_spareBlock : static_cast<T*>(malloc(blockSize));
  73     m_spareBlock = 0;
  74
  75     m_blocks.append(block);
  76     return block;
  77 }
  78
  79 template <typename T> void BlockStack<T>::shrink(T* newEnd)
  80 {
  81     ASSERT(newEnd != m_blocks.last() + blockLength);
  82     m_spareBlock = m_blocks.last();
  83     m_blocks.removeLast();
  84
  85     while (m_blocks.last() + blockLength != newEnd) {
  86         free(m_blocks.last());
  87         m_blocks.removeLast();
  88     }
  89 }
  90
  91 }
  92
  93 using WTF::BlockStack;
  94
  95 #endif