Specifying Message Control Information

In addition to the message buffers, IXCMSGOX allows you to pass 32 bytes of user-defined message control information using the MSGCNTL parameter. The message control information is included in the message exit parameter list (MEPL) passed to the receiving member's message user routine. If message control information is provided when sending a response, the information is included in the message notification parameter list (MNPL) passed to the originator's message notify user routine.

You can use the message control information area to hold whatever information you like. XCF members planning to send messages to one another should agree on how the message control information is to be used, for example to:

Indicate where to store the message if multiple users will share access to the message data
Identify the format of the message or message parts so the message data can be accessed correctly
Pass additional information needed to receive the data
Identify the message so it can be acknowledged by the receiver
Hold the message data, if the message is 32 bytes or less.