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Diffstat (limited to 'xpcom/base/nsIClassInfoImpl.h')
| -rw-r--r-- | xpcom/base/nsIClassInfoImpl.h | 193 |
1 files changed, 193 insertions, 0 deletions
diff --git a/xpcom/base/nsIClassInfoImpl.h b/xpcom/base/nsIClassInfoImpl.h new file mode 100644 index 0000000000..045e75e5af --- /dev/null +++ b/xpcom/base/nsIClassInfoImpl.h @@ -0,0 +1,193 @@ +/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */ +/* vim: set ts=8 sts=2 et sw=2 tw=80: */ +/* This Source Code Form is subject to the terms of the Mozilla Public + * License, v. 2.0. If a copy of the MPL was not distributed with this + * file, You can obtain one at http://mozilla.org/MPL/2.0/. */ + +#ifndef nsIClassInfoImpl_h__ +#define nsIClassInfoImpl_h__ + +#include "mozilla/Alignment.h" +#include "mozilla/Assertions.h" +#include "mozilla/MacroArgs.h" +#include "mozilla/MacroForEach.h" +#include "nsIClassInfo.h" +#include "nsISupportsImpl.h" + +#include <new> + +/** + * This header file provides macros which help you make your class implement + * nsIClassInfo. Implementing nsIClassInfo is particularly helpful if you have + * a C++ class which implements multiple interfaces and which you access from + * JavaScript. If that class implements nsIClassInfo, the JavaScript code + * won't have to call QueryInterface on instances of the class; all methods + * from all interfaces returned by GetInterfaces() will be available + * automagically. + * + * Here's all you need to do. Given a class + * + * class nsFooBar : public nsIFoo, public nsIBar { }; + * + * you should already have the following nsISupports implementation in its cpp + * file: + * + * NS_IMPL_ISUPPORTS(nsFooBar, nsIFoo, nsIBar). + * + * Change this to + * + * NS_IMPL_CLASSINFO(nsFooBar, nullptr, 0, NS_FOOBAR_CID) + * NS_IMPL_ISUPPORTS_CI(nsFooBar, nsIFoo, nsIBar) + * + * If nsFooBar is threadsafe, change the 0 above to nsIClassInfo::THREADSAFE. + * If it's a singleton, use nsIClassInfo::SINGLETON. The full list of flags is + * in nsIClassInfo.idl. + * + * The nullptr parameter is there so you can pass a function for converting + * from an XPCOM object to a scriptable helper. Unless you're doing + * specialized JS work, you can probably leave this as nullptr. + * + * This file also defines the NS_IMPL_QUERY_INTERFACE_CI macro, which you can + * use to replace NS_IMPL_QUERY_INTERFACE, if you use that instead of + * NS_IMPL_ISUPPORTS. + * + * That's it! The rest is gory details. + * + * + * Notice that nsFooBar didn't need to inherit from nsIClassInfo in order to + * "implement" it. However, after adding these macros to nsFooBar, you you can + * QueryInterface an instance of nsFooBar to nsIClassInfo. How can this be? + * + * The answer lies in the NS_IMPL_ISUPPORTS_CI macro. It modifies nsFooBar's + * QueryInterface implementation such that, if we ask to QI to nsIClassInfo, it + * returns a singleton object associated with the class. (That singleton is + * defined by NS_IMPL_CLASSINFO.) So all nsFooBar instances will return the + * same object when QI'ed to nsIClassInfo. (You can see this in + * NS_IMPL_QUERY_CLASSINFO below.) + * + * This hack breaks XPCOM's rules, since if you take an instance of nsFooBar, + * QI it to nsIClassInfo, and then try to QI to nsIFoo, that will fail. On the + * upside, implementing nsIClassInfo doesn't add a vtable pointer to instances + * of your class. + * + * In principal, you can also implement nsIClassInfo by inheriting from the + * interface. But some code expects that when it QI's an object to + * nsIClassInfo, it gets back a singleton which isn't attached to any + * particular object. If a class were to implement nsIClassInfo through + * inheritance, that code might QI to nsIClassInfo and keep the resulting + * object alive, thinking it was only keeping alive the classinfo singleton, + * but in fact keeping a whole instance of the class alive. See, e.g., bug + * 658632. + * + * Unless you specifically need to have a different nsIClassInfo instance for + * each instance of your class, you should probably just implement nsIClassInfo + * as a singleton. + */ + +class GenericClassInfo : public nsIClassInfo { + public: + struct ClassInfoData { + // This function pointer uses NS_CALLBACK_ because it's always set to an + // NS_IMETHOD function, which uses __stdcall on Win32. + typedef NS_CALLBACK_(nsresult, GetInterfacesProc)(nsTArray<nsIID>& aArray); + GetInterfacesProc getinterfaces; + + // This function pointer doesn't use NS_CALLBACK_ because it's always set to + // a vanilla function. + typedef nsresult (*GetScriptableHelperProc)(nsIXPCScriptable** aHelper); + GetScriptableHelperProc getscriptablehelper; + + uint32_t flags; + nsCID cid; + }; + + NS_DECL_ISUPPORTS_INHERITED + NS_DECL_NSICLASSINFO + + explicit GenericClassInfo(const ClassInfoData* aData) : mData(aData) {} + + private: + const ClassInfoData* mData; +}; + +#define NS_CLASSINFO_NAME(_class) g##_class##_classInfoGlobal +#define NS_CI_INTERFACE_GETTER_NAME(_class) _class##_GetInterfacesHelper +#define NS_DECL_CI_INTERFACE_GETTER(_class) \ + extern NS_IMETHODIMP NS_CI_INTERFACE_GETTER_NAME(_class)(nsTArray<nsIID> & \ + array); + +#define NS_IMPL_CLASSINFO(_class, _getscriptablehelper, _flags, _cid) \ + NS_DECL_CI_INTERFACE_GETTER(_class) \ + static const GenericClassInfo::ClassInfoData k##_class##ClassInfoData = { \ + NS_CI_INTERFACE_GETTER_NAME(_class), \ + _getscriptablehelper, \ + _flags | nsIClassInfo::SINGLETON_CLASSINFO, \ + _cid, \ + }; \ + mozilla::AlignedStorage2<GenericClassInfo> k##_class##ClassInfoDataPlace; \ + nsIClassInfo* NS_CLASSINFO_NAME(_class) = nullptr; + +#define NS_IMPL_QUERY_CLASSINFO(_class) \ + if (aIID.Equals(NS_GET_IID(nsIClassInfo))) { \ + if (!NS_CLASSINFO_NAME(_class)) \ + NS_CLASSINFO_NAME(_class) = new (k##_class##ClassInfoDataPlace.addr()) \ + GenericClassInfo(&k##_class##ClassInfoData); \ + foundInterface = NS_CLASSINFO_NAME(_class); \ + } else + +#define NS_CLASSINFO_HELPER_BEGIN(_class, _c) \ + NS_IMETHODIMP \ + NS_CI_INTERFACE_GETTER_NAME(_class)(nsTArray<nsIID> & array) { \ + array.Clear(); \ + array.SetCapacity(_c); + +#define NS_CLASSINFO_HELPER_ENTRY(_interface) \ + array.AppendElement(NS_GET_IID(_interface)); + +#define NS_CLASSINFO_HELPER_END \ + return NS_OK; \ + } + +#define NS_IMPL_CI_INTERFACE_GETTER(aClass, ...) \ + static_assert(MOZ_ARG_COUNT(__VA_ARGS__) > 0, \ + "Need more arguments to NS_IMPL_CI_INTERFACE_GETTER"); \ + NS_CLASSINFO_HELPER_BEGIN(aClass, MOZ_ARG_COUNT(__VA_ARGS__)) \ + MOZ_FOR_EACH(NS_CLASSINFO_HELPER_ENTRY, (), (__VA_ARGS__)) \ + NS_CLASSINFO_HELPER_END + +#define NS_IMPL_CI_INTERFACE_GETTER0(aClass) \ + NS_CLASSINFO_HELPER_BEGIN(aClass, 0) \ + NS_CLASSINFO_HELPER_END + +// Note that this macro is an internal implementation of this header and +// should not be used outside it. It does not end the interface map as this +// is done in NS_IMPL_QUERY_INTERFACE_CI or the _INHERITED variant. +#define NS_IMPL_QUERY_INTERFACE_CI_GUTS(aClass, ...) \ + static_assert(MOZ_ARG_COUNT(__VA_ARGS__) > 0, \ + "Need more arguments to NS_IMPL_QUERY_INTERFACE_CI"); \ + NS_INTERFACE_MAP_BEGIN(aClass) \ + MOZ_FOR_EACH(NS_INTERFACE_MAP_ENTRY, (), (__VA_ARGS__)) \ + NS_INTERFACE_MAP_ENTRY_AMBIGUOUS(nsISupports, MOZ_ARG_1(__VA_ARGS__)) \ + NS_IMPL_QUERY_CLASSINFO(aClass) + +#define NS_IMPL_QUERY_INTERFACE_CI(aClass, ...) \ + NS_IMPL_QUERY_INTERFACE_CI_GUTS(aClass, __VA_ARGS__) \ + NS_INTERFACE_MAP_END + +#define NS_IMPL_QUERY_INTERFACE_CI_INHERITED(aClass, aSuper, ...) \ + NS_IMPL_QUERY_INTERFACE_CI_GUTS(aClass, __VA_ARGS__) \ + NS_INTERFACE_MAP_END_INHERITING \ + (aSuper) + +#define NS_IMPL_QUERY_INTERFACE_CI_INHERITED0(aClass, aSuper) \ + NS_INTERFACE_MAP_BEGIN(aClass) \ + NS_IMPL_QUERY_CLASSINFO(aClass) \ + NS_INTERFACE_MAP_END_INHERITING(aSuper) + +#define NS_IMPL_ISUPPORTS_CI(aClass, ...) \ + NS_IMPL_ADDREF(aClass) \ + NS_IMPL_RELEASE(aClass) \ + NS_IMPL_QUERY_INTERFACE_CI(aClass, __VA_ARGS__) \ + NS_IMPL_CI_INTERFACE_GETTER(aClass, __VA_ARGS__) + +#endif // nsIClassInfoImpl_h__ |