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Article ID: 96781 - Last Review: July 13, 2004 - Revision: 1.1
How To Use RPC Callback Functions
This article was previously published under Q96781
The standard remote procedure call (RPC) model has a server containing one
or more exported function calls, and a client, which calls the server's
exported functions. However, Microsoft's implementation of RPC defines
callbacks as a special interface definition language (IDL) attribute
allowing a server to call a client function.
Callbacks can be used only in the context of a server call. Thus, a server
may call a client's callback function only when the server is performing a
client's remote procedure call (before it returns from processing). For
example:
CLIENT SERVER
------ ------
Client makes RPC call. --->
<--- Server calls callback procedure.
Client returns from callback. --->
<--- Server calls callback procedure.
Client returns from callback. --->
<--- Server returns from original RPC call.
Callbacks are declared in the RPC .IDL file and defined in the source of
the client. The following demonstrates how callbacks are declared and
defined:
[ SAMPLE.IDL ]
[
uuid(9FEE4F51-0396-101A-AE4F-08002B2D0065),
version(1.0),
pointer_default( unique )
]
{
void RPCProc( [in, string] unsigned char *pszStr );
[callback] void CallbackProc([in,string] unsigned char *pszStr);
}
[ SAMPLEC.C (Client)]
/*
Callback RPC call (initiated from server, executed on client).
*/
void CallbackProc( unsigned char *pszString )
{
printf("Call from server, printed on client: %s", pszStr );
}
[ SAMPLES.C (Server)]
/*
"Standard" RPC call (initiated from client, executed on server).
Makes a call to client callback procedure, CallbackProc().
*/
void RPCProc( unsigned char *pszStr )
{
printf("About to call Callback() client function.."
CallbackProc( pszStr );
printf("Called callback function.");
}
In the makefile for the sample, the "-ms_ext" switch must be used for the
MIDL compile. For example:
midl -ms_ext -cpp_cmd $(cc) -cpp_opt "-E" sample.idl
APPLIES TO
- Microsoft Win32 Software Development Kit (SDK) 3.1
- Microsoft Win32 Software Development Kit (SDK) 3.5
- Microsoft Win32 Software Development Kit (SDK) 3.51
- Microsoft Win32 Software Development Kit (SDK) 4.0
| kbhowto kbapi kbrpc kbnetwork KB96781 |
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