Usage notes

 

Here are some general points to consider when writing your exit program:

• For performance reasons, write your program in assembler language. If you write it in any of the other languages supported by WebSphere MQ for z/OS, provide your own data definition file.

• Link-edit your program as AMODE(31) and RMODE(ANY).

• To define the exit parameter block to your program, use the assembler-language macro, CMQXPA.

• If you are using the CICS Transaction Server for OS/390 storage protection feature, your program must run in CICS execution key. That is, specify EXECKEY(CICS) when defining both your exit program and any programs to which it passes control. For information about CICS exit programs and the CICS storage protection facility, see the CICS Customization Guide.

• Your program can use all the APIs (for example, IMS, DB2, and CICS) that a CICS task-related user exit program can use. It can also use any of the MQI calls except MQCONN, MQCONNX, and MQDISC. However, any MQI calls within the exit program do not invoke the exit program a second time.

• Your program can issue EXEC CICS SYNCPOINT or EXEC CICS SYNCPOINT ROLLBACK commands. However, these commands commit or roll back all the updates done by the task up to the point that the exit was used, and so their use is not recommended.

• Your program must end by issuing an EXEC CICS RETURN command. It must not transfer control with an XCTL command.

• Exits are written as extensions to the WebSphere MQ for z/OS code. Ensure that your exit does not disrupt any WebSphere MQ for z/OS programs or transactions that use the MQI. These are usually indicated with a prefix of CSQ or CK.

• If CSQCAPX is defined to CICS, the CICS system attempts to load the exit program when CICS connects to WebSphere MQ for z/OS. If this attempt is successful, message CSQC301I is sent to the CKQC panel or to the system console. If the load is unsuccessful (for example, if the load module does not exist in any of the libraries in the DFHRPL concatenation), message CSQC315 is sent to the CKQC panel or to the system console.

• Because the parameters in the communication area are addresses, the exit program must be defined as local to the CICS system (that is, not as a remote program).

 

Parent topic:

Writing your own exit program

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