1/*
2 * Copyright (C) 2012-2019 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#pragma once
27
28#include "CellContainer.h"
29#include "WeakImpl.h"
30#include <wtf/DoublyLinkedList.h>
31#include <wtf/StdLibExtras.h>
32
33namespace JSC {
34
35class Heap;
36class SlotVisitor;
37
38class WeakBlock : public DoublyLinkedListNode<WeakBlock> {
39public:
40 friend class WTF::DoublyLinkedListNode<WeakBlock>;
41 static constexpr size_t blockSize = 256; // 1/16 of MarkedBlock size
42
43 struct FreeCell {
44 FreeCell* next;
45 };
46
47 struct SweepResult {
48 bool isNull() const;
49
50 bool blockIsFree { true };
51 bool blockIsLogicallyEmpty { true };
52 FreeCell* freeList { nullptr };
53 };
54
55 static WeakBlock* create(Heap&, CellContainer);
56 static void destroy(Heap&, WeakBlock*);
57
58 static WeakImpl* asWeakImpl(FreeCell*);
59
60 bool isEmpty();
61 bool isLogicallyEmptyButNotFree() const;
62
63 void sweep();
64 SweepResult takeSweepResult();
65
66 void visit(SlotVisitor&);
67
68 void reap();
69
70 void lastChanceToFinalize();
71 void disconnectContainer() { m_container = CellContainer(); }
72
73private:
74 static FreeCell* asFreeCell(WeakImpl*);
75
76 template<typename ContainerType>
77 void specializedVisit(ContainerType&, SlotVisitor&);
78
79 explicit WeakBlock(CellContainer);
80 void finalize(WeakImpl*);
81 WeakImpl* weakImpls();
82 size_t weakImplCount();
83 void addToFreeList(FreeCell**, WeakImpl*);
84
85 CellContainer m_container;
86 WeakBlock* m_prev;
87 WeakBlock* m_next;
88 SweepResult m_sweepResult;
89};
90
91inline bool WeakBlock::SweepResult::isNull() const
92{
93 return blockIsFree && !freeList; // This state is impossible, so we can use it to mean null.
94}
95
96inline WeakImpl* WeakBlock::asWeakImpl(FreeCell* freeCell)
97{
98 return reinterpret_cast_ptr<WeakImpl*>(freeCell);
99}
100
101inline WeakBlock::SweepResult WeakBlock::takeSweepResult()
102{
103 SweepResult tmp;
104 std::swap(tmp, m_sweepResult);
105 ASSERT(m_sweepResult.isNull());
106 return tmp;
107}
108
109inline WeakBlock::FreeCell* WeakBlock::asFreeCell(WeakImpl* weakImpl)
110{
111 return reinterpret_cast_ptr<FreeCell*>(weakImpl);
112}
113
114inline WeakImpl* WeakBlock::weakImpls()
115{
116 return reinterpret_cast_ptr<WeakImpl*>(this) + ((sizeof(WeakBlock) + sizeof(WeakImpl) - 1) / sizeof(WeakImpl));
117}
118
119inline size_t WeakBlock::weakImplCount()
120{
121 return (blockSize / sizeof(WeakImpl)) - ((sizeof(WeakBlock) + sizeof(WeakImpl) - 1) / sizeof(WeakImpl));
122}
123
124inline void WeakBlock::addToFreeList(FreeCell** freeList, WeakImpl* weakImpl)
125{
126 ASSERT(weakImpl->state() == WeakImpl::Deallocated);
127 FreeCell* freeCell = asFreeCell(weakImpl);
128 ASSERT(!*freeList || ((char*)*freeList > (char*)this && (char*)*freeList < (char*)this + blockSize));
129 ASSERT((char*)freeCell > (char*)this && (char*)freeCell < (char*)this + blockSize);
130 freeCell->next = *freeList;
131 *freeList = freeCell;
132}
133
134inline bool WeakBlock::isEmpty()
135{
136 return !m_sweepResult.isNull() && m_sweepResult.blockIsFree;
137}
138
139inline bool WeakBlock::isLogicallyEmptyButNotFree() const
140{
141 return !m_sweepResult.isNull() && !m_sweepResult.blockIsFree && m_sweepResult.blockIsLogicallyEmpty;
142}
143
144} // namespace JSC
145