tools/TieredMMapArray.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. ``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 #ifndef TieredMMapArray_h
  27 #define TieredMMapArray_h
  28
  29 #include <wtf/OSAllocator.h>
  30
  31 namespace JSC {
  32
  33 // This class implements a simple array class that can be grown by appending items to the end.
  34 // This class is implemented purely in terms of system allocations, with no malloc/free, so that
  35 // it can safely be used from a secondary thread whilst the main thrad is paused (potentially
  36 // holding the fast malloc heap lock).
  37 template<typename T>
  38 class TieredMMapArray {
  39     static const size_t entriesPerBlock = 4096;
  40
  41 public:
  42     TieredMMapArray()
  43         : m_directoryCount(4096)
  44         , m_directory(static_cast<T**>(OSAllocator::reserveAndCommit(m_directoryCount * sizeof(T*))))
  45         , m_size(0)
  46     {
  47         for (size_t block = 0; block < m_directoryCount; ++block)
  48             m_directory[block] = 0;
  49     }
  50
  51     ~TieredMMapArray()
  52     {
  53         size_t usedCount = (m_size + (entriesPerBlock - 1)) / entriesPerBlock;
  54         ASSERT(usedCount == m_directoryCount || !m_directory[usedCount]);
  55
  56         for (size_t block = 0; block < usedCount; ++block) {
  57             ASSERT(m_directory[block]);
  58             OSAllocator::decommitAndRelease(m_directory[block], entriesPerBlock * sizeof(T));
  59         }
  60
  61         OSAllocator::decommitAndRelease(m_directory, m_directoryCount * sizeof(T*));
  62     }
  63
  64     T& operator[](size_t index)
  65     {
  66         ASSERT(index < m_size);
  67         size_t block = index / entriesPerBlock;
  68         size_t offset = index % entriesPerBlock;
  69
  70         ASSERT(m_directory[block]);
  71         return m_directory[block][offset];
  72     }
  73
  74     void append(const T& value)
  75     {
  76         // Check if the array is completely full, if so create more capacity in the directory.
  77         if (m_size == m_directoryCount * entriesPerBlock) {
  78             // Reallocate the directory.
  79             size_t oldDirectorySize = m_directoryCount * sizeof(T*);
  80             size_t newDirectorySize = oldDirectorySize * 2;
  81             RELEASE_ASSERT(newDirectorySize < oldDirectorySize);
  82             m_directory = OSAllocator::reallocateCommitted(m_directory, oldDirectorySize, newDirectorySize);
  83
  84             //
  85             size_t newDirectoryCount = m_directoryCount * 2;
  86             for (size_t block = m_directoryCount; block < newDirectoryCount; ++block)
  87                 m_directory[block] = 0;
  88             m_directoryCount = newDirectoryCount;
  89         }
  90
  91         size_t index = m_size;
  92         size_t block = index / entriesPerBlock;
  93         size_t offset = index % entriesPerBlock;
  94
  95         if (!offset) {
  96             ASSERT(!m_directory[block]);
  97             m_directory[block] = static_cast<T*>(OSAllocator::reserveAndCommit(entriesPerBlock * sizeof(T)));
  98         }
  99
 100         ASSERT(m_directory[block]);
 101         ++m_size;
 102         m_directory[block][offset] = value;
 103     }
 104
 105     size_t size() const { return m_size; }
 106
 107 private:
 108     size_t m_directoryCount;
 109     T** m_directory;
 110     size_t m_size;
 111 };
 112
 113 }
 114
 115 #endif // TieredMMapArray_h
 116