mirror of
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176 lines
8.0 KiB
C++
176 lines
8.0 KiB
C++
/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
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/* vim: set ts=8 sts=2 et sw=2 tw=80: */
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/* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
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#ifndef nsIClassInfoImpl_h__
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#define nsIClassInfoImpl_h__
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#include "mozilla/Alignment.h"
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#include "mozilla/Assertions.h"
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#include "mozilla/MacroArgs.h"
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#include "mozilla/MacroForEach.h"
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#include "nsIClassInfo.h"
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#include "nsISupportsImpl.h"
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#include <new>
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/**
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* This header file provides macros which help you make your class implement
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* nsIClassInfo. Implementing nsIClassInfo is particularly helpful if you have
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* a C++ class which implements multiple interfaces and which you access from
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* JavaScript. If that class implements nsIClassInfo, the JavaScript code
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* won't have to call QueryInterface on instances of the class; all methods
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* from all interfaces returned by GetInterfaces() will be available
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* automagically.
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*
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* Here's all you need to do. Given a class
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*
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* class nsFooBar : public nsIFoo, public nsIBar { };
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*
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* you should already have the following nsISupports implementation in its cpp
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* file:
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*
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* NS_IMPL_ISUPPORTS(nsFooBar, nsIFoo, nsIBar).
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*
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* Change this to
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*
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* NS_IMPL_CLASSINFO(nsFooBar, nullptr, 0, NS_FOOBAR_CID)
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* NS_IMPL_ISUPPORTS_CI(nsFooBar, nsIFoo, nsIBar)
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*
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* If nsFooBar is threadsafe, change the 0 above to nsIClassInfo::THREADSAFE.
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* If it's a singleton, use nsIClassInfo::SINGLETON. The full list of flags is
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* in nsIClassInfo.idl.
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*
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* The nullptr parameter is there so you can pass a function for converting
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* from an XPCOM object to a scriptable helper. Unless you're doing
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* specialized JS work, you can probably leave this as nullptr.
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*
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* This file also defines the NS_IMPL_QUERY_INTERFACE_CI macro, which you can
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* use to replace NS_IMPL_QUERY_INTERFACE, if you use that instead of
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* NS_IMPL_ISUPPORTS.
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*
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* That's it! The rest is gory details.
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*
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*
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* Notice that nsFooBar didn't need to inherit from nsIClassInfo in order to
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* "implement" it. However, after adding these macros to nsFooBar, you you can
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* QueryInterface an instance of nsFooBar to nsIClassInfo. How can this be?
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*
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* The answer lies in the NS_IMPL_ISUPPORTS_CI macro. It modifies nsFooBar's
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* QueryInterface implementation such that, if we ask to QI to nsIClassInfo, it
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* returns a singleton object associated with the class. (That singleton is
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* defined by NS_IMPL_CLASSINFO.) So all nsFooBar instances will return the
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* same object when QI'ed to nsIClassInfo. (You can see this in
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* NS_IMPL_QUERY_CLASSINFO below.)
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*
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* This hack breaks XPCOM's rules, since if you take an instance of nsFooBar,
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* QI it to nsIClassInfo, and then try to QI to nsIFoo, that will fail. On the
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* upside, implementing nsIClassInfo doesn't add a vtable pointer to instances
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* of your class.
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*
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* In principal, you can also implement nsIClassInfo by inheriting from the
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* interface. But some code expects that when it QI's an object to
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* nsIClassInfo, it gets back a singleton which isn't attached to any
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* particular object. If a class were to implement nsIClassInfo through
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* inheritance, that code might QI to nsIClassInfo and keep the resulting
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* object alive, thinking it was only keeping alive the classinfo singleton,
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* but in fact keeping a whole instance of the class alive. See, e.g., bug
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* 658632.
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*
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* Unless you specifically need to have a different nsIClassInfo instance for
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* each instance of your class, you should probably just implement nsIClassInfo
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* as a singleton.
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*/
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class GenericClassInfo : public nsIClassInfo
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{
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public:
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struct ClassInfoData
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{
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typedef NS_CALLBACK(GetInterfacesProc)(uint32_t* aCountP,
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nsIID*** aArray);
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typedef NS_CALLBACK(GetScriptableHelperProc)(nsIXPCScriptable** aHelper);
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GetInterfacesProc getinterfaces;
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GetScriptableHelperProc getscriptablehelper;
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uint32_t flags;
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nsCID cid;
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};
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NS_DECL_ISUPPORTS_INHERITED
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NS_DECL_NSICLASSINFO
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explicit GenericClassInfo(const ClassInfoData* aData) : mData(aData) {}
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private:
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const ClassInfoData* mData;
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};
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#define NS_CLASSINFO_NAME(_class) g##_class##_classInfoGlobal
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#define NS_CI_INTERFACE_GETTER_NAME(_class) _class##_GetInterfacesHelper
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#define NS_DECL_CI_INTERFACE_GETTER(_class) \
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extern NS_IMETHODIMP NS_CI_INTERFACE_GETTER_NAME(_class) \
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(uint32_t *, nsIID ***);
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#define NS_IMPL_CLASSINFO(_class, _getscriptablehelper, _flags, _cid) \
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NS_DECL_CI_INTERFACE_GETTER(_class) \
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static const GenericClassInfo::ClassInfoData k##_class##ClassInfoData = { \
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NS_CI_INTERFACE_GETTER_NAME(_class), \
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_getscriptablehelper, \
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_flags | nsIClassInfo::SINGLETON_CLASSINFO, \
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_cid, \
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}; \
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mozilla::AlignedStorage2<GenericClassInfo> k##_class##ClassInfoDataPlace; \
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nsIClassInfo* NS_CLASSINFO_NAME(_class) = nullptr;
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#define NS_IMPL_QUERY_CLASSINFO(_class) \
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if ( aIID.Equals(NS_GET_IID(nsIClassInfo)) ) { \
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if (!NS_CLASSINFO_NAME(_class)) \
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NS_CLASSINFO_NAME(_class) = new (k##_class##ClassInfoDataPlace.addr()) \
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GenericClassInfo(&k##_class##ClassInfoData); \
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foundInterface = NS_CLASSINFO_NAME(_class); \
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} else
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#define NS_CLASSINFO_HELPER_BEGIN(_class, _c) \
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NS_IMETHODIMP \
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NS_CI_INTERFACE_GETTER_NAME(_class)(uint32_t *count, nsIID ***array) \
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{ \
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*count = _c; \
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*array = (nsIID **)moz_xmalloc(sizeof (nsIID *) * _c); \
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uint32_t i = 0;
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#define NS_CLASSINFO_HELPER_ENTRY(_interface) \
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(*array)[i++] = (nsIID*)nsMemory::Clone(&NS_GET_IID(_interface), \
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sizeof(nsIID));
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#define NS_CLASSINFO_HELPER_END \
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MOZ_ASSERT(i == *count, "Incorrent number of entries"); \
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return NS_OK; \
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}
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#define NS_IMPL_CI_INTERFACE_GETTER(aClass, ...) \
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MOZ_STATIC_ASSERT_VALID_ARG_COUNT(__VA_ARGS__); \
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NS_CLASSINFO_HELPER_BEGIN(aClass, \
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MOZ_PASTE_PREFIX_AND_ARG_COUNT(/* No prefix */, \
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__VA_ARGS__)) \
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MOZ_FOR_EACH(NS_CLASSINFO_HELPER_ENTRY, (), (__VA_ARGS__)) \
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NS_CLASSINFO_HELPER_END
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#define NS_IMPL_QUERY_INTERFACE_CI(aClass, ...) \
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MOZ_STATIC_ASSERT_VALID_ARG_COUNT(__VA_ARGS__); \
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NS_INTERFACE_MAP_BEGIN(aClass) \
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MOZ_FOR_EACH(NS_INTERFACE_MAP_ENTRY, (), (__VA_ARGS__)) \
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NS_INTERFACE_MAP_ENTRY_AMBIGUOUS(nsISupports, MOZ_ARG_1(__VA_ARGS__)) \
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NS_IMPL_QUERY_CLASSINFO(aClass) \
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NS_INTERFACE_MAP_END
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#define NS_IMPL_ISUPPORTS_CI(aClass, ...) \
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NS_IMPL_ADDREF(aClass) \
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NS_IMPL_RELEASE(aClass) \
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NS_IMPL_QUERY_INTERFACE_CI(aClass, __VA_ARGS__) \
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NS_IMPL_CI_INTERFACE_GETTER(aClass, __VA_ARGS__)
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#endif // nsIClassInfoImpl_h__
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