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