mirror of
https://github.com/mozilla/gecko-dev.git
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252 lines
8.9 KiB
C++
252 lines
8.9 KiB
C++
/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
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/* ***** BEGIN LICENSE BLOCK *****
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* Version: MPL 1.1/GPL 2.0/LGPL 2.1
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*
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* The contents of this file are subject to the Mozilla Public License Version
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* 1.1 (the "License"); you may not use this file except in compliance with
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* the License. You may obtain a copy of the License at
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* http://www.mozilla.org/MPL/
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*
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* Software distributed under the License is distributed on an "AS IS" basis,
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* WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
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* for the specific language governing rights and limitations under the
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* License.
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*
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* The Original Code is Gecko DOM code.
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*
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* The Initial Developer of the Original Code is
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* Mozilla Foundation.
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* Portions created by the Initial Developer are Copyright (C) 2008
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* the Initial Developer. All Rights Reserved.
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*
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* Contributor(s):
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* Peter Van der Beken <peterv@propagandism.org>
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*
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* Alternatively, the contents of this file may be used under the terms of
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* either the GNU General Public License Version 2 or later (the "GPL"), or
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* the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
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* in which case the provisions of the GPL or the LGPL are applicable instead
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* of those above. If you wish to allow use of your version of this file only
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* under the terms of either the GPL or the LGPL, and not to allow others to
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* use your version of this file under the terms of the MPL, indicate your
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* decision by deleting the provisions above and replace them with the notice
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* and other provisions required by the GPL or the LGPL. If you do not delete
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* the provisions above, a recipient may use your version of this file under
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* the terms of any one of the MPL, the GPL or the LGPL.
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*
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* ***** END LICENSE BLOCK ***** */
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#ifndef nsWrapperCache_h___
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#define nsWrapperCache_h___
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#include "nsCycleCollectionParticipant.h"
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struct JSObject;
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struct JSContext;
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class nsContentUtils;
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class XPCWrappedNativeScope;
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typedef PRUptrdiff PtrBits;
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#define NS_WRAPPERCACHE_IID \
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{ 0x6f3179a1, 0x36f7, 0x4a5c, \
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{ 0x8c, 0xf1, 0xad, 0xc8, 0x7c, 0xde, 0x3e, 0x87 } }
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/**
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* Class to store the wrapper for an object. This can only be used with objects
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* that only have one non-security wrapper at a time (for an XPCWrappedNative
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* this is usually ensured by setting an explicit parent in the PreCreate hook
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* for the class).
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*
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* An instance of nsWrapperCache can be gotten from an object that implements
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* a wrapper cache by calling QueryInterface on it. Note that this breaks XPCOM
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* rules a bit (this object doesn't derive from nsISupports).
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*
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* The cache can store objects other than wrappers. We allow wrappers to use a
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* separate JSObject to store their state (mostly expandos). If the wrapper is
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* collected and we want to preserve this state we actually store the state
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* object in the cache.
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*
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* The cache can store 3 types of objects:
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*
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* If WRAPPER_IS_PROXY is not set (IsProxy() returns false):
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* - a slim wrapper or the JSObject of an XPCWrappedNative wrapper
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*
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* If WRAPPER_IS_PROXY is set (IsProxy() returns true):
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* - a proxy wrapper
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* - an expando object
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*
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* If a proxy wrapper is GCed and it has an expando object we'll store the
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* expando object in the cache. If we create a new proxy wrapper and the cache
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* contains an expando object we'll store the expando object in the new wrapper
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* and store the new wrapper in the cache. Unlinking from the cycle collector
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* clears anything stored in the cache.
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*
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* A number of the methods are implemented in nsWrapperCacheInlines.h because we
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* have to include some JS headers that don't play nicely with the rest of the
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* codebase. Include nsWrapperCacheInlines.h if you need to call those methods.
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*/
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class nsWrapperCache
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{
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friend class nsContentUtils;
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public:
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NS_DECLARE_STATIC_IID_ACCESSOR(NS_WRAPPERCACHE_IID)
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nsWrapperCache() : mWrapperPtrBits(0)
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{
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}
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~nsWrapperCache()
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{
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NS_ASSERTION(!PreservingWrapper(),
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"Destroying cache with a preserved wrapper!");
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RemoveExpandoObject();
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}
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/**
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* Get the cached wrapper.
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*
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* This getter clears the gray bit before handing out the JSObject which means
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* that the object is guaranteed to be kept alive past the next CC.
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*/
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JSObject* GetWrapper() const;
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/**
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* Get the cached wrapper.
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*
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* This getter does not change the color of the JSObject meaning that the
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* object returned is not guaranteed to be kept alive past the next CC.
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*
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* This should only be called if you are certain that the return value won't
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* be passed into a JS API function and that it won't be stored without being
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* rooted (or otherwise signaling the stored value to the CC).
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*/
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JSObject* GetWrapperPreserveColor() const;
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/**
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* Get the expando object, used for storing expando properties, if there is
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* one available. If the cache holds a DOM proxy binding that proxy's expando
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* object will be returned.
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*
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* This getter does not change the color of the JSObject meaning that the
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* object returned is not guaranteed to be kept alive past the next CC.
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*
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* This should only be called if you are certain that the return value won't
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* be passed into a JS API function and that it won't be stored without being
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* rooted (or otherwise signaling the stored value to the CC).
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*/
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JSObject* GetExpandoObjectPreserveColor() const;
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void SetWrapper(JSObject* aWrapper);
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/**
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* Clear the wrapper, but keep the expando object alive if the wrapper has
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* one. This should be called from the finalizer for the wrapper.
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*/
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void ClearWrapper();
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/**
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* Clear the wrapper if it's a proxy, doesn't keep the expando object alive.
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* This should be called when unlinking the cache.
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*/
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void ClearWrapperIfProxy();
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bool PreservingWrapper()
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{
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return (mWrapperPtrBits & WRAPPER_BIT_PRESERVED) != 0;
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}
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void SetIsProxy()
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{
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NS_ASSERTION(!mWrapperPtrBits,
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"This flag should be set before creating any wrappers.");
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mWrapperPtrBits = WRAPPER_IS_PROXY;
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}
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void ClearIsProxy()
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{
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NS_ASSERTION(!mWrapperPtrBits || mWrapperPtrBits == WRAPPER_IS_PROXY,
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"This flag should be cleared before creating any wrappers.");
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mWrapperPtrBits = 0;
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}
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bool IsProxy() const
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{
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return (mWrapperPtrBits & WRAPPER_IS_PROXY) != 0;
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}
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/**
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* Wrap the object corresponding to this wrapper cache. If non-null is
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* returned, the object has already been stored in the wrapper cache and the
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* value set in triedToWrap is meaningless. If null is returned then
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* triedToWrap indicates whether an error occurred, if it's false then the
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* object doesn't actually support creating a wrapper through its WrapObject
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* hook.
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*/
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virtual JSObject* WrapObject(JSContext *cx, XPCWrappedNativeScope *scope,
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bool *triedToWrap)
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{
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*triedToWrap = false;
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return nsnull;
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}
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private:
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// Only meant to be called by nsContentUtils.
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void SetPreservingWrapper(bool aPreserve)
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{
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if(aPreserve) {
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mWrapperPtrBits |= WRAPPER_BIT_PRESERVED;
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}
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else {
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mWrapperPtrBits &= ~WRAPPER_BIT_PRESERVED;
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}
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}
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JSObject *GetJSObjectFromBits() const
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{
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return reinterpret_cast<JSObject*>(mWrapperPtrBits & ~kWrapperBitMask);
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}
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void SetWrapperBits(void *aWrapper)
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{
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mWrapperPtrBits = reinterpret_cast<PtrBits>(aWrapper) |
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(mWrapperPtrBits & WRAPPER_IS_PROXY);
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}
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void RemoveExpandoObject();
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static JSObject *GetExpandoFromSlot(JSObject *obj);
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/**
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* If this bit is set then we're preserving the wrapper, which in effect ties
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* the lifetime of the JS object stored in the cache to the lifetime of the
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* native object. We rely on the cycle collector to break the cycle that this
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* causes between the native object and the JS object, so it is important that
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* any native object that supports preserving of its wrapper
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* traces/traverses/unlinks the cached JS object (see
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* NS_IMPL_CYCLE_COLLECTION_TRACE_PRESERVED_WRAPPER,
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* NS_IMPL_CYCLE_COLLECTION_TRAVERSE_SCRIPT_OBJECTS and
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* NS_IMPL_CYCLE_COLLECTION_UNLINK_PRESERVED_WRAPPER).
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*/
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enum { WRAPPER_BIT_PRESERVED = 1 << 0 };
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/**
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* If this bit is set then the wrapper for the native object is a proxy. Note
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* that that doesn't necessarily mean that the JS object stored in the cache
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* is a JS proxy, as we sometimes store objects other than the wrapper in the
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* cache.
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*/
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enum { WRAPPER_IS_PROXY = 1 << 1 };
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enum { kWrapperBitMask = (WRAPPER_BIT_PRESERVED | WRAPPER_IS_PROXY) };
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PtrBits mWrapperPtrBits;
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};
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NS_DEFINE_STATIC_IID_ACCESSOR(nsWrapperCache, NS_WRAPPERCACHE_IID)
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#define NS_WRAPPERCACHE_INTERFACE_MAP_ENTRY \
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if ( aIID.Equals(NS_GET_IID(nsWrapperCache)) ) { \
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*aInstancePtr = static_cast<nsWrapperCache*>(this); \
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return NS_OK; \
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}
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#endif /* nsWrapperCache_h___ */
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