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1 // Copyright 2015 The Chromium Authors. All rights reserved. | |
2 // Use of this source code is governed by a BSD-style license that can be | |
3 // found in the LICENSE file. | |
4 | |
5 #ifndef PersistentNode_h | |
6 #define PersistentNode_h | |
7 | |
8 #include "platform/heap/ThreadState.h" | |
9 #include "wtf/Assertions.h" | |
10 #include "wtf/MainThread.h" | |
11 #include "wtf/ThreadingPrimitives.h" | |
12 | |
13 namespace blink { | |
14 | |
15 class PersistentNode final { | |
16 public: | |
17 PersistentNode() | |
18 : m_self(nullptr) | |
19 , m_trace(nullptr) | |
20 { | |
21 ASSERT(isFree()); | |
22 } | |
23 | |
24 ~PersistentNode() | |
25 { | |
26 // If you hit this assert, it means that the thread finished | |
27 // without clearing persistent handles that the thread created. | |
28 // We don't enable the assert for the main thread because the | |
29 // main thread finishes without clearing all persistent handles. | |
30 ASSERT(isMainThread() || isFree()); | |
31 } | |
32 | |
33 // It is dangrous to copy the PersistentNode because it breaks the | |
34 // free list. | |
35 PersistentNode& operator=(const PersistentNode& otherref) = delete; | |
36 | |
37 // Ideally the trace method should be virtual and automatically dispatch | |
38 // to the most specific implementation. However having a virtual method | |
39 // on PersistentNode leads to too eager template instantiation with MSVC | |
40 // which leads to include cycles. | |
41 // Instead we call the constructor with a TraceCallback which knows the | |
42 // type of the most specific child and calls trace directly. See | |
43 // TraceMethodDelegate in Visitor.h for how this is done. | |
44 void tracePersistentNode(Visitor* visitor) | |
45 { | |
46 ASSERT(!isFree()); | |
47 ASSERT(m_trace); | |
48 m_trace(visitor, m_self); | |
49 } | |
50 | |
51 void initialize(void* self, TraceCallback trace) | |
52 { | |
53 ASSERT(isFree()); | |
54 m_self = self; | |
55 m_trace = trace; | |
56 } | |
57 | |
58 void setFreeNext(PersistentNode* node) | |
59 { | |
60 ASSERT(!node || node->isFree()); | |
61 m_self = node; | |
62 m_trace = nullptr; | |
63 ASSERT(isFree()); | |
64 } | |
65 | |
66 PersistentNode* freeNext() | |
67 { | |
68 ASSERT(isFree()); | |
69 PersistentNode* node = reinterpret_cast<PersistentNode*>(m_self); | |
70 ASSERT(!node || node->isFree()); | |
71 return node; | |
72 } | |
73 | |
74 bool isFree() const | |
sof
2015/06/30 09:19:39
"free" feels a bit overloaded in this context - "u
haraken
2015/06/30 09:51:32
Done.
| |
75 { | |
76 return !m_trace; | |
77 } | |
78 | |
79 private: | |
80 // If this PersistentNode is in use: | |
81 // - m_self points to the corresponding Persistent handle. | |
82 // - m_trace points to the trace method. | |
83 // If this PersistentNode is freed: | |
84 // - m_self points to the next freed PersistentNode. | |
85 // - m_trace is nullptr. | |
86 void* m_self; | |
87 TraceCallback m_trace; | |
88 }; | |
89 | |
90 struct PersistentNodeSlots final { | |
91 private: | |
92 static const int slotCount = 256; | |
93 PersistentNodeSlots* m_next; | |
94 PersistentNode m_slot[slotCount]; | |
95 friend class PersistentRegion; | |
96 }; | |
97 | |
98 class PersistentRegion final { | |
sof
2015/06/30 09:19:39
Could you add a comment outlining what this provid
| |
99 public: | |
100 PersistentRegion() | |
101 : m_freeHead(nullptr) | |
102 , m_slots(nullptr) | |
103 #if ENABLE(ASSERT) | |
104 , m_numberOfPersistents(0) | |
105 #endif | |
106 { | |
107 } | |
108 ~PersistentRegion(); | |
109 | |
110 PersistentNode* allocatePersistentNode(void* self, TraceCallback trace) | |
111 { | |
112 #if ENABLE(ASSERT) | |
113 ++m_numberOfPersistents; | |
114 #endif | |
115 if (UNLIKELY(!m_freeHead)) | |
116 ensurePersistentNodeSlots(self, trace); | |
117 ASSERT(m_freeHead); | |
118 PersistentNode* node = m_freeHead; | |
119 m_freeHead = m_freeHead->freeNext(); | |
120 node->initialize(self, trace); | |
121 ASSERT(!node->isFree()); | |
122 return node; | |
123 } | |
124 void ensurePersistentNodeSlots(void*, TraceCallback); | |
sof
2015/06/30 09:19:39
make this private?
haraken
2015/06/30 09:51:32
Done.
| |
125 void freePersistentNode(PersistentNode* persistentNode) | |
126 { | |
127 ASSERT(m_numberOfPersistents > 0); | |
128 persistentNode->setFreeNext(m_freeHead); | |
129 m_freeHead = persistentNode; | |
130 #if ENABLE(ASSERT) | |
131 --m_numberOfPersistents; | |
132 #endif | |
133 } | |
134 void tracePersistentNodes(Visitor*); | |
135 int numberOfPersistents(); | |
136 | |
137 private: | |
138 PersistentNode* m_freeHead; | |
139 PersistentNodeSlots* m_slots; | |
140 #if ENABLE(ASSERT) | |
141 int m_numberOfPersistents; | |
sof
2015/06/30 09:19:39
Did you consider caching this count outside of ENA
haraken
2015/06/30 09:51:32
At first I did this, but it added extra overhead t
| |
142 #endif | |
143 }; | |
144 | |
145 class CrossThreadPersistentRegion final { | |
146 public: | |
147 CrossThreadPersistentRegion() : m_persistentRegion(adoptPtr(new PersistentRe gion)) { } | |
148 | |
149 PersistentNode* allocatePersistentNode(void* self, TraceCallback trace) | |
150 { | |
151 MutexLocker lock(m_mutex); | |
152 return m_persistentRegion->allocatePersistentNode(self, trace); | |
153 } | |
154 | |
155 void freePersistentNode(PersistentNode* persistentNode) | |
156 { | |
157 MutexLocker lock(m_mutex); | |
158 m_persistentRegion->freePersistentNode(persistentNode); | |
159 } | |
160 | |
161 void tracePersistentNodes(Visitor* visitor) | |
162 { | |
163 MutexLocker lock(m_mutex); | |
164 m_persistentRegion->tracePersistentNodes(visitor); | |
165 } | |
166 | |
167 private: | |
168 // We don't make CrossThreadPersistentRegion inherit from PersistentRegion | |
169 // because we don't want to virtualize performance-sensitive methods | |
170 // such as PersistentRegion::allocate/freePersistentNode. | |
171 OwnPtr<PersistentRegion> m_persistentRegion; | |
172 Mutex m_mutex; | |
173 }; | |
174 | |
175 } // namespace blink | |
176 | |
177 #endif | |
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