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nsIClassInfoImpl.h
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/
nsIClassInfoImpl.h
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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* 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(GetInterfacesProc)(uint32_t* aCountP, 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) \
(uint32_t *, nsIID ***);
#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)(uint32_t *count, nsIID ***array) \
{ \
*count = _c; \
*array = (nsIID **)moz_xmalloc(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__