diff -r 000000000000 -r 6474c204b198 xpcom/glue/nsIClassInfoImpl.h --- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/xpcom/glue/nsIClassInfoImpl.h Wed Dec 31 06:09:35 2014 +0100 @@ -0,0 +1,176 @@ +/* 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 + +/** + * 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 NS_COM_GLUE GenericClassInfo : public nsIClassInfo +{ +public: + struct ClassInfoData + { + typedef NS_CALLBACK(GetInterfacesProc)(uint32_t* countp, + nsIID*** array); + typedef NS_CALLBACK(GetLanguageHelperProc)(uint32_t language, + nsISupports** helper); + + GetInterfacesProc getinterfaces; + GetLanguageHelperProc getlanguagehelper; + uint32_t flags; + nsCID cid; + }; + + NS_DECL_ISUPPORTS_INHERITED + NS_DECL_NSICLASSINFO + + GenericClassInfo(const ClassInfoData* data) + : mData(data) + { } + +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) \ + (uint32_t *, nsIID ***); + +#define NS_IMPL_CLASSINFO(_class, _getlanguagehelper, _flags, _cid) \ + NS_DECL_CI_INTERFACE_GETTER(_class) \ + static const GenericClassInfo::ClassInfoData k##_class##ClassInfoData = { \ + NS_CI_INTERFACE_GETTER_NAME(_class), \ + _getlanguagehelper, \ + _flags | nsIClassInfo::SINGLETON_CLASSINFO, \ + _cid, \ + }; \ + mozilla::AlignedStorage2 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)(uint32_t *count, nsIID ***array) \ +{ \ + *count = _c; \ + *array = (nsIID **)nsMemory::Alloc(sizeof (nsIID *) * _c); \ + uint32_t i = 0; + +#define NS_CLASSINFO_HELPER_ENTRY(_interface) \ + (*array)[i++] = (nsIID*)nsMemory::Clone(&NS_GET_IID(_interface), \ + sizeof(nsIID)); + +#define NS_CLASSINFO_HELPER_END \ + MOZ_ASSERT(i == *count, "Incorrent number of entries"); \ + return NS_OK; \ +} + +#define NS_IMPL_CI_INTERFACE_GETTER(aClass, ...) \ + MOZ_STATIC_ASSERT_VALID_ARG_COUNT(__VA_ARGS__); \ + NS_CLASSINFO_HELPER_BEGIN(aClass, \ + MOZ_PASTE_PREFIX_AND_ARG_COUNT(/* No prefix */, \ + __VA_ARGS__)) \ + MOZ_FOR_EACH(NS_CLASSINFO_HELPER_ENTRY, (), (__VA_ARGS__)) \ + NS_CLASSINFO_HELPER_END + +#define NS_IMPL_QUERY_INTERFACE_CI(aClass, ...) \ + MOZ_STATIC_ASSERT_VALID_ARG_COUNT(__VA_ARGS__); \ + 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) \ + NS_INTERFACE_MAP_END + +#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__