z/OS: Changes to exits

From IBM MQ for z/OS® Version 9.0.0, exits that rely upon being able to modify static storage within the load module must be modified to be reentrant.

Writing channel exit programs on z/OS stipulates that IBM MQ exits must be reentrant and capable of running anywhere in virtual storage.

Non-reentrant C programs are those that might use variables declared with the static storage class, or variables receiving the extern storage class, or might contain writable static strings.

Non-reentrant exits have, technically, never been supported in IBM MQ for z/OS, but prior to IBM MQ for z/OS Version 9.0.0, it was possible for some of these exits to process successfully

From IBM MQ for z/OS Version 9.0.0, exits that rely upon being able to modify static storage within the load module no longer function correctly. You should modify such exits to be reentrant.

• Moving static or global variables inside the scope of a function, or
• Dynamically allocating storage used for any static variables and using, for example, the IBM MQ ExitUserArea, or other operating system facilities, such as name or token services to obtain addressability.