Your message notify user routine provides a mechanism for XCF to notify members of events related to the use of the XCF signaling service. When you join an XCF group, you can specify the address of a message notify user routine to be given control when XCF needs to provide this notification. You can also specify the address of a message notify user routine when invoking the IXCMSGOX service to send a message or on the IXCMSGC Call Exit service to call a user routine. The system gives preference to the user routine specified on the invoked IXCMSGOX or IXCMSGC service when a message notify user routine is also specified on IXCJOIN.