1 /*
2 * Copyright (C) 2009 Google 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 are
6 * met:
7 *
8 * * Redistributions of source code must retain the above copyright
9 * notice, this list of conditions and the following disclaimer.
10 * * Redistributions in binary form must reproduce the above
11 * copyright notice, this list of conditions and the following disclaimer
12 * in the documentation and/or other materials provided with the
13 * distribution.
14 * * Neither the name of Google Inc. nor the names of its
15 * contributors may be used to endorse or promote products derived from
16 * this software without specific prior written permission.
17 *
18 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
19 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
20 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
21 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
22 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
23 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
24 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
25 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
26 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
27 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
28 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
29 */
30
31 #include "config.h"
32 #include "DOMDataStore.h"
33
34 #include "DOMData.h"
35
36 namespace WebCore {
37
38 // DOM binding algorithm:
39 //
40 // There are two kinds of DOM objects:
41 // 1. DOM tree nodes, such as Document, HTMLElement, ...
42 // there classes implement TreeShared<T> interface;
43 // 2. Non-node DOM objects, such as CSSRule, Location, etc.
44 // these classes implement a ref-counted scheme.
45 //
46 // A DOM object may have a JS wrapper object. If a tree node
47 // is alive, its JS wrapper must be kept alive even it is not
48 // reachable from JS roots.
49 // However, JS wrappers of non-node objects can go away if
50 // not reachable from other JS objects. It works like a cache.
51 //
52 // DOM objects are ref-counted, and JS objects are traced from
53 // a set of root objects. They can create a cycle. To break
54 // cycles, we do following:
55 // Handles from DOM objects to JS wrappers are always weak,
56 // so JS wrappers of non-node object cannot create a cycle.
57 // Before starting a global GC, we create a virtual connection
58 // between nodes in the same tree in the JS heap. If the wrapper
59 // of one node in a tree is alive, wrappers of all nodes in
60 // the same tree are considered alive. This is done by creating
61 // object groups in GC prologue callbacks. The mark-compact
62 // collector will remove these groups after each GC.
63 //
64 // DOM objects should be deref-ed from the owning thread, not the GC thread
65 // that does not own them. In V8, GC can kick in from any thread. To ensure
66 // that DOM objects are always deref-ed from the owning thread when running
67 // V8 in multi-threading environment, we do following:
68 // 1. Maintain a thread specific DOM wrapper map for each object map.
69 // (We're using TLS support from WTF instead of base since V8Bindings
70 // does not depend on base. We further assume that all child threads
71 // running V8 instances are created by WTF and thus a destructor will
72 // be called to clean up all thread specific data.)
73 // 2. When GC happens:
74 // 2.1. If the dead object is in GC thread's map, remove the JS reference
75 // and deref the DOM object.
76 // 2.2. Otherwise, go through all thread maps to find the owning thread.
77 // Remove the JS reference from the owning thread's map and move the
78 // DOM object to a delayed queue. Post a task to the owning thread
79 // to have it deref-ed from the owning thread at later time.
80 // 3. When a thread is tearing down, invoke a cleanup routine to go through
81 // all objects in the delayed queue and the thread map and deref all of
82 // them.
83
84
DOMDataStore(DOMData * domData)85 DOMDataStore::DOMDataStore(DOMData* domData)
86 : m_domNodeMap(0)
87 , m_domObjectMap(0)
88 , m_activeDomObjectMap(0)
89 #if ENABLE(SVG)
90 , m_domSvgElementInstanceMap(0)
91 #endif
92 , m_domData(domData)
93 {
94 WTF::MutexLocker locker(DOMDataStore::allStoresMutex());
95 DOMDataStore::allStores().append(this);
96 }
97
~DOMDataStore()98 DOMDataStore::~DOMDataStore()
99 {
100 WTF::MutexLocker locker(DOMDataStore::allStoresMutex());
101 DOMDataStore::allStores().remove(DOMDataStore::allStores().find(this));
102 }
103
allStores()104 DOMDataList& DOMDataStore::allStores()
105 {
106 DEFINE_STATIC_LOCAL(DOMDataList, staticDOMDataList, ());
107 return staticDOMDataList;
108 }
109
allStoresMutex()110 WTF::Mutex& DOMDataStore::allStoresMutex()
111 {
112 DEFINE_STATIC_LOCAL(WTF::Mutex, staticDOMDataListMutex, ());
113 return staticDOMDataListMutex;
114 }
115
getDOMWrapperMap(DOMWrapperMapType type)116 void* DOMDataStore::getDOMWrapperMap(DOMWrapperMapType type)
117 {
118 switch (type) {
119 case DOMNodeMap:
120 return m_domNodeMap;
121 case DOMObjectMap:
122 return m_domObjectMap;
123 case ActiveDOMObjectMap:
124 return m_activeDomObjectMap;
125 #if ENABLE(SVG)
126 case DOMSVGElementInstanceMap:
127 return m_domSvgElementInstanceMap;
128 #endif
129 }
130
131 ASSERT_NOT_REACHED();
132 return 0;
133 }
134
135 // Called when the object is near death (not reachable from JS roots).
136 // It is time to remove the entry from the table and dispose the handle.
weakDOMObjectCallback(v8::Persistent<v8::Value> v8Object,void * domObject)137 void DOMDataStore::weakDOMObjectCallback(v8::Persistent<v8::Value> v8Object, void* domObject)
138 {
139 v8::HandleScope scope;
140 ASSERT(v8Object->IsObject());
141 DOMData::handleWeakObject(DOMDataStore::DOMObjectMap, v8::Persistent<v8::Object>::Cast(v8Object), domObject);
142 }
143
weakActiveDOMObjectCallback(v8::Persistent<v8::Value> v8Object,void * domObject)144 void DOMDataStore::weakActiveDOMObjectCallback(v8::Persistent<v8::Value> v8Object, void* domObject)
145 {
146 v8::HandleScope scope;
147 ASSERT(v8Object->IsObject());
148 DOMData::handleWeakObject(DOMDataStore::ActiveDOMObjectMap, v8::Persistent<v8::Object>::Cast(v8Object), domObject);
149 }
150
weakNodeCallback(v8::Persistent<v8::Value> value,void * domObject)151 void DOMDataStore::weakNodeCallback(v8::Persistent<v8::Value> value, void* domObject)
152 {
153 ASSERT(WTF::isMainThread());
154
155 Node* node = static_cast<Node*>(domObject);
156 // Node wrappers must be JS objects.
157 v8::Persistent<v8::Object> v8Object = v8::Persistent<v8::Object>::Cast(value);
158
159 WTF::MutexLocker locker(DOMDataStore::allStoresMutex());
160 DOMDataList& list = DOMDataStore::allStores();
161 for (size_t i = 0; i < list.size(); ++i) {
162 DOMDataStore* store = list[i];
163 if (store->domNodeMap().removeIfPresent(node, v8Object)) {
164 ASSERT(store->domData()->owningThread() == WTF::currentThread());
165 node->deref(); // Nobody overrides Node::deref so it's safe
166 return; // There might be at most one wrapper for the node in world's maps
167 }
168 }
169
170 // If not found, it means map for the wrapper has been already destroyed, just dispose the
171 // handle and deref the object to fight memory leak.
172 v8Object.Dispose();
173 node->deref(); // Nobody overrides Node::deref so it's safe
174 }
175
176 #if ENABLE(SVG)
177
weakSVGElementInstanceCallback(v8::Persistent<v8::Value> v8Object,void * domObject)178 void DOMDataStore::weakSVGElementInstanceCallback(v8::Persistent<v8::Value> v8Object, void* domObject)
179 {
180 v8::HandleScope scope;
181 ASSERT(v8Object->IsObject());
182 DOMData::handleWeakObject(DOMDataStore::DOMSVGElementInstanceMap, v8::Persistent<v8::Object>::Cast(v8Object), static_cast<SVGElementInstance*>(domObject));
183 }
184
185 #endif // ENABLE(SVG)
186
187 } // namespace WebCore
188