The following guidance applies specifically to cluster workload exit programs. Read it in conjunction with the general application-programming guidance given in the WebSphere MQ Application Programming Guide.
Cluster workload exits are invoked as if by a z/OS LINK in:
Put the link-edited modules in the data set specified by the CSQXLIB DD statement of the queue manager address space procedure. The names of the load modules are specified as the workload exit names in the queue-manager definition.
When writing workload exits for WebSphere MQ for z/OS, the following rules apply:
Note that there are no absolute restrictions on what you can do in an exit. However, most SVCs involve waits, so avoid them, except for the following:
Do not use ESTAEs and ESPIEs because their error handling might interfere with the error handling performed by WebSphere MQ(R). This means that WebSphere MQ might not be able to recover from an error, or that your exit program might not receive all the error information.
The system parameter EXITLIM, which is described in the WebSphere MQ for z/OS System Setup Guide, limits the amount of time an exit may run for. The default value for EXITLIM is 30 seconds. If you see the return code MQRC_CLUSTER_EXIT_ERROR (2266 X'8DA') your exit may be looping. If you think the exit needs more than 30 seconds to complete, increase the value of EXITLIM.
Cluster workload exits must not use MQI calls. In other respects, the rules for writing and compiling cluster workload exit programs are similar to the rules that apply to channel exit programs. These are described in detail in the WebSphere MQ Intercommunication book.
For information about building your application, see the WebSphere MQ Application Programming Guide and the WebSphere MQ Intercommunication book. However you need to resolve the MQXCLWLN function by linking with the mqutl library on Windows NT(R) or the libmqutl library on the UNIX platforms.
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