1 : /* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
2 : /* ***** BEGIN LICENSE BLOCK *****
3 : * Version: MPL 1.1/GPL 2.0/LGPL 2.1
4 : *
5 : * The contents of this file are subject to the Mozilla Public License Version
6 : * 1.1 (the "License"); you may not use this file except in compliance with
7 : * the License. You may obtain a copy of the License at
8 : * http://www.mozilla.org/MPL/
9 : *
10 : * Software distributed under the License is distributed on an "AS IS" basis,
11 : * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
12 : * for the specific language governing rights and limitations under the
13 : * License.
14 : *
15 : * The Original Code is Gecko DOM code.
16 : *
17 : * The Initial Developer of the Original Code is
18 : * Mozilla Foundation.
19 : * Portions created by the Initial Developer are Copyright (C) 2008
20 : * the Initial Developer. All Rights Reserved.
21 : *
22 : * Contributor(s):
23 : * Peter Van der Beken <peterv@propagandism.org>
24 : *
25 : * Alternatively, the contents of this file may be used under the terms of
26 : * either the GNU General Public License Version 2 or later (the "GPL"), or
27 : * the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
28 : * in which case the provisions of the GPL or the LGPL are applicable instead
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30 : * under the terms of either the GPL or the LGPL, and not to allow others to
31 : * use your version of this file under the terms of the MPL, indicate your
32 : * decision by deleting the provisions above and replace them with the notice
33 : * and other provisions required by the GPL or the LGPL. If you do not delete
34 : * the provisions above, a recipient may use your version of this file under
35 : * the terms of any one of the MPL, the GPL or the LGPL.
36 : *
37 : * ***** END LICENSE BLOCK ***** */
38 :
39 : #ifndef nsWrapperCache_h___
40 : #define nsWrapperCache_h___
41 :
42 : #include "nsCycleCollectionParticipant.h"
43 :
44 : struct JSObject;
45 : struct JSContext;
46 : class nsContentUtils;
47 : class XPCWrappedNativeScope;
48 :
49 : typedef PRUptrdiff PtrBits;
50 :
51 : #define NS_WRAPPERCACHE_IID \
52 : { 0x6f3179a1, 0x36f7, 0x4a5c, \
53 : { 0x8c, 0xf1, 0xad, 0xc8, 0x7c, 0xde, 0x3e, 0x87 } }
54 :
55 : /**
56 : * Class to store the wrapper for an object. This can only be used with objects
57 : * that only have one non-security wrapper at a time (for an XPCWrappedNative
58 : * this is usually ensured by setting an explicit parent in the PreCreate hook
59 : * for the class).
60 : *
61 : * An instance of nsWrapperCache can be gotten from an object that implements
62 : * a wrapper cache by calling QueryInterface on it. Note that this breaks XPCOM
63 : * rules a bit (this object doesn't derive from nsISupports).
64 : *
65 : * The cache can store objects other than wrappers. We allow wrappers to use a
66 : * separate JSObject to store their state (mostly expandos). If the wrapper is
67 : * collected and we want to preserve this state we actually store the state
68 : * object in the cache.
69 : *
70 : * The cache can store 3 types of objects:
71 : *
72 : * If WRAPPER_IS_PROXY is not set (IsProxy() returns false):
73 : * - a slim wrapper or the JSObject of an XPCWrappedNative wrapper
74 : *
75 : * If WRAPPER_IS_PROXY is set (IsProxy() returns true):
76 : * - a proxy wrapper
77 : * - an expando object
78 : *
79 : * If a proxy wrapper is GCed and it has an expando object we'll store the
80 : * expando object in the cache. If we create a new proxy wrapper and the cache
81 : * contains an expando object we'll store the expando object in the new wrapper
82 : * and store the new wrapper in the cache. Unlinking from the cycle collector
83 : * clears anything stored in the cache.
84 : *
85 : * A number of the methods are implemented in nsWrapperCacheInlines.h because we
86 : * have to include some JS headers that don't play nicely with the rest of the
87 : * codebase. Include nsWrapperCacheInlines.h if you need to call those methods.
88 : */
89 : class nsWrapperCache
90 : {
91 : friend class nsContentUtils;
92 :
93 : public:
94 : NS_DECLARE_STATIC_IID_ACCESSOR(NS_WRAPPERCACHE_IID)
95 :
96 0 : nsWrapperCache() : mWrapperPtrBits(0)
97 : {
98 0 : }
99 0 : ~nsWrapperCache()
100 0 : {
101 0 : NS_ASSERTION(!PreservingWrapper(),
102 : "Destroying cache with a preserved wrapper!");
103 0 : RemoveExpandoObject();
104 0 : }
105 :
106 : /**
107 : * Get the cached wrapper.
108 : *
109 : * This getter clears the gray bit before handing out the JSObject which means
110 : * that the object is guaranteed to be kept alive past the next CC.
111 : */
112 : JSObject* GetWrapper() const;
113 :
114 : /**
115 : * Get the cached wrapper.
116 : *
117 : * This getter does not change the color of the JSObject meaning that the
118 : * object returned is not guaranteed to be kept alive past the next CC.
119 : *
120 : * This should only be called if you are certain that the return value won't
121 : * be passed into a JS API function and that it won't be stored without being
122 : * rooted (or otherwise signaling the stored value to the CC).
123 : */
124 : JSObject* GetWrapperPreserveColor() const;
125 :
126 : /**
127 : * Get the expando object, used for storing expando properties, if there is
128 : * one available. If the cache holds a DOM proxy binding that proxy's expando
129 : * object will be returned.
130 : *
131 : * This getter does not change the color of the JSObject meaning that the
132 : * object returned is not guaranteed to be kept alive past the next CC.
133 : *
134 : * This should only be called if you are certain that the return value won't
135 : * be passed into a JS API function and that it won't be stored without being
136 : * rooted (or otherwise signaling the stored value to the CC).
137 : */
138 : JSObject* GetExpandoObjectPreserveColor() const;
139 :
140 : void SetWrapper(JSObject* aWrapper);
141 :
142 : /**
143 : * Clear the wrapper, but keep the expando object alive if the wrapper has
144 : * one. This should be called from the finalizer for the wrapper.
145 : */
146 : void ClearWrapper();
147 :
148 : /**
149 : * Clear the wrapper if it's a proxy, doesn't keep the expando object alive.
150 : * This should be called when unlinking the cache.
151 : */
152 : void ClearWrapperIfProxy();
153 :
154 0 : bool PreservingWrapper()
155 : {
156 0 : return (mWrapperPtrBits & WRAPPER_BIT_PRESERVED) != 0;
157 : }
158 :
159 : void SetIsProxy()
160 : {
161 : NS_ASSERTION(!mWrapperPtrBits,
162 : "This flag should be set before creating any wrappers.");
163 : mWrapperPtrBits = WRAPPER_IS_PROXY;
164 : }
165 0 : void ClearIsProxy()
166 : {
167 0 : NS_ASSERTION(!mWrapperPtrBits || mWrapperPtrBits == WRAPPER_IS_PROXY,
168 : "This flag should be cleared before creating any wrappers.");
169 0 : mWrapperPtrBits = 0;
170 0 : }
171 :
172 0 : bool IsProxy() const
173 : {
174 0 : return (mWrapperPtrBits & WRAPPER_IS_PROXY) != 0;
175 : }
176 :
177 :
178 : /**
179 : * Wrap the object corresponding to this wrapper cache. If non-null is
180 : * returned, the object has already been stored in the wrapper cache and the
181 : * value set in triedToWrap is meaningless. If null is returned then
182 : * triedToWrap indicates whether an error occurred, if it's false then the
183 : * object doesn't actually support creating a wrapper through its WrapObject
184 : * hook.
185 : */
186 0 : virtual JSObject* WrapObject(JSContext *cx, XPCWrappedNativeScope *scope,
187 : bool *triedToWrap)
188 : {
189 0 : *triedToWrap = false;
190 0 : return nsnull;
191 : }
192 :
193 : /**
194 : * Returns true if the object has a non-gray wrapper.
195 : */
196 : bool IsBlack();
197 :
198 : private:
199 : // Only meant to be called by nsContentUtils.
200 0 : void SetPreservingWrapper(bool aPreserve)
201 : {
202 0 : if(aPreserve) {
203 0 : mWrapperPtrBits |= WRAPPER_BIT_PRESERVED;
204 : }
205 : else {
206 0 : mWrapperPtrBits &= ~WRAPPER_BIT_PRESERVED;
207 : }
208 0 : }
209 0 : JSObject *GetJSObjectFromBits() const
210 : {
211 0 : return reinterpret_cast<JSObject*>(mWrapperPtrBits & ~kWrapperBitMask);
212 : }
213 0 : void SetWrapperBits(void *aWrapper)
214 : {
215 : mWrapperPtrBits = reinterpret_cast<PtrBits>(aWrapper) |
216 0 : (mWrapperPtrBits & WRAPPER_IS_PROXY);
217 0 : }
218 : void RemoveExpandoObject();
219 :
220 : static JSObject *GetExpandoFromSlot(JSObject *obj);
221 :
222 : /**
223 : * If this bit is set then we're preserving the wrapper, which in effect ties
224 : * the lifetime of the JS object stored in the cache to the lifetime of the
225 : * native object. We rely on the cycle collector to break the cycle that this
226 : * causes between the native object and the JS object, so it is important that
227 : * any native object that supports preserving of its wrapper
228 : * traces/traverses/unlinks the cached JS object (see
229 : * NS_IMPL_CYCLE_COLLECTION_TRACE_PRESERVED_WRAPPER,
230 : * NS_IMPL_CYCLE_COLLECTION_TRAVERSE_SCRIPT_OBJECTS and
231 : * NS_IMPL_CYCLE_COLLECTION_UNLINK_PRESERVED_WRAPPER).
232 : */
233 : enum { WRAPPER_BIT_PRESERVED = 1 << 0 };
234 :
235 : /**
236 : * If this bit is set then the wrapper for the native object is a proxy. Note
237 : * that that doesn't necessarily mean that the JS object stored in the cache
238 : * is a JS proxy, as we sometimes store objects other than the wrapper in the
239 : * cache.
240 : */
241 : enum { WRAPPER_IS_PROXY = 1 << 1 };
242 :
243 : enum { kWrapperBitMask = (WRAPPER_BIT_PRESERVED | WRAPPER_IS_PROXY) };
244 :
245 : PtrBits mWrapperPtrBits;
246 : };
247 :
248 : NS_DEFINE_STATIC_IID_ACCESSOR(nsWrapperCache, NS_WRAPPERCACHE_IID)
249 :
250 : #define NS_WRAPPERCACHE_INTERFACE_MAP_ENTRY \
251 : if ( aIID.Equals(NS_GET_IID(nsWrapperCache)) ) { \
252 : *aInstancePtr = static_cast<nsWrapperCache*>(this); \
253 : return NS_OK; \
254 : }
255 :
256 : #endif /* nsWrapperCache_h___ */
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