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 WeakBlock_h
27#define WeakBlock_h
28
29#include "HeapBlock.h"
30#include "WeakHandleOwner.h"
31#include "WeakImpl.h"
32#include <wtf/DoublyLinkedList.h>
33#include <wtf/StdLibExtras.h>
34
35namespace JSC {
36
37class DeadBlock;
38class HeapRootVisitor;
39class JSValue;
40class WeakHandleOwner;
41
42class WeakBlock : public HeapBlock<WeakBlock> {
43public:
44    friend class WTF::DoublyLinkedListNode<WeakBlock>;
45    static const size_t blockSize = 4 * KB; // 5% of MarkedBlock size
46
47    struct FreeCell {
48        FreeCell* next;
49    };
50
51    struct SweepResult {
52        SweepResult();
53        bool isNull() const;
54
55        bool blockIsFree;
56        FreeCell* freeList;
57    };
58
59    static WeakBlock* create(DeadBlock*);
60
61    static WeakImpl* asWeakImpl(FreeCell*);
62
63    bool isEmpty();
64
65    void sweep();
66    SweepResult takeSweepResult();
67
68    void visit(HeapRootVisitor&);
69    void reap();
70
71    void lastChanceToFinalize();
72
73private:
74    static FreeCell* asFreeCell(WeakImpl*);
75
76    WeakBlock(Region*);
77    WeakImpl* firstWeakImpl();
78    void finalize(WeakImpl*);
79    WeakImpl* weakImpls();
80    size_t weakImplCount();
81    void addToFreeList(FreeCell**, WeakImpl*);
82
83    SweepResult m_sweepResult;
84};
85
86inline WeakBlock::SweepResult::SweepResult()
87    : blockIsFree(true)
88    , freeList(0)
89{
90    ASSERT(isNull());
91}
92
93inline bool WeakBlock::SweepResult::isNull() const
94{
95    return blockIsFree && !freeList; // This state is impossible, so we can use it to mean null.
96}
97
98inline WeakImpl* WeakBlock::asWeakImpl(FreeCell* freeCell)
99{
100    return reinterpret_cast_ptr<WeakImpl*>(freeCell);
101}
102
103inline WeakBlock::SweepResult WeakBlock::takeSweepResult()
104{
105    SweepResult tmp;
106    std::swap(tmp, m_sweepResult);
107    ASSERT(m_sweepResult.isNull());
108    return tmp;
109}
110
111inline WeakBlock::FreeCell* WeakBlock::asFreeCell(WeakImpl* weakImpl)
112{
113    return reinterpret_cast_ptr<FreeCell*>(weakImpl);
114}
115
116inline WeakImpl* WeakBlock::weakImpls()
117{
118    return reinterpret_cast_ptr<WeakImpl*>(this) + ((sizeof(WeakBlock) + sizeof(WeakImpl) - 1) / sizeof(WeakImpl));
119}
120
121inline size_t WeakBlock::weakImplCount()
122{
123    return (blockSize / sizeof(WeakImpl)) - ((sizeof(WeakBlock) + sizeof(WeakImpl) - 1) / sizeof(WeakImpl));
124}
125
126inline void WeakBlock::addToFreeList(FreeCell** freeList, WeakImpl* weakImpl)
127{
128    ASSERT(weakImpl->state() == WeakImpl::Deallocated);
129    FreeCell* freeCell = asFreeCell(weakImpl);
130    ASSERT(!*freeList || ((char*)*freeList > (char*)this && (char*)*freeList < (char*)this + blockSize));
131    ASSERT((char*)freeCell > (char*)this && (char*)freeCell < (char*)this + blockSize);
132    freeCell->next = *freeList;
133    *freeList = freeCell;
134}
135
136inline bool WeakBlock::isEmpty()
137{
138    return !m_sweepResult.isNull() && m_sweepResult.blockIsFree;
139}
140
141} // namespace JSC
142
143#endif // WeakBlock_h
144