Sending a Synchronous Message

Specify REQTYPE=SYNC on IXZXIXSM to indicate that the message is sent synchronously so the sender waits until receiving the acknowledgement before continuing processing. This option also indicates that JES XCF provides recovery even if the receiving member fails prior to receiving or acknowledging the message.

This option is useful when:

A member needs data from another member and must wait until that data is received before processing can continue.
For example, in a JES3 complex, the local main requires a spool buffer; the local cannot continue its current processing until the global main returns that data.
The message data is critical to your installation's continued immediate processing. The sender needs to know that the message data was received and requires JES XCF to attempt to resend that data if it was not received.
For example, in Figure 1, the local processor (MCR) sends a synchronous message (a spool allocation request) to the global processor (POK). The member MCR cannot continue any further work until the request is satisfied by the member POK. Therefore, a wait is not relevant to MCR's performance; it is an absolute necessity before MCR continues any further work. Member MCR sends the message, waits for the acknowledgement, and eventually receives the spool space and continues work.
Figure 1. Example synchronous message request

Unless a synchronous message is absolutely necessary, do not use this form of sending messages. Be certain to issue a REQTYPE=SYNC message request only in environments other than the JES main task.