FORCEQR

The FORCEQR system initialization parameter specifies whether you want CICS® to force all CICS API user application programs that are specified as threadsafe to run under the CICS quasi-reentrant (QR) task control block (TCB), as if they were specified as quasi-reentrant programs.

If your programs are defined as quasi-reentrant, CICS always calls them under the CICS QR TCB. The requirements for a quasi-reentrant program in a multithreading context are less stringent than if the program were to execute concurrently on multiple TCBs. CICS requires that an application program is reentrant so that it guarantees consistent conditions. In practice, an application program may not be truly reentrant; CICS expects "quasi-reentrancy". This means that the application program should be in a consistent state when control is passed to it, both on entry, and before and after each EXEC CICS command. Such quasi-reentrancy guarantees that each invocation of an application program is unaffected by previous runs, or by concurrent multi-threading through the program by multiple CICS tasks.

CICS quasi-reentrant user programs (application programs, user-replaceable modules, global user exits, and task-related user exits) are given control by the CICS dispatcher under the QR TCB. When running under this TCB, a program can be sure that no other quasi-reentrant program can run until it relinquishes control during a CICS request, at which point the user task is suspended, leaving the program still "in use". The same program can then be reinvoked for another task, which means the application program can be in use concurrently by more than one task, although only one task at a time can actually be executing.

Running application with programs defined as threadsafe to use OTE, such as CICS Db2® applications, could cause problems if one or more programs is not threadsafe. Using the FORCEQR system initialization parameter, you can force all your applications onto the QR TCB.

Forcing applications on the QR TCB is useful in production regions where you cannot afford to have applications out of service while you investigate the problem.

The default for this parameter is FORCEQR=NO, which means that CICS honors the CONCURRENCY attribute on your program resource definitions. As a temporary measure, while you investigate and resolve problems connected with threadsafe-defined programs, you can set FORCEQR=YES. When all problems have been resolved, resetting FORCEQR=NO makes all programs resume use of open TCBs under the OTE.

The FORCEQR parameter applies to all programs defined as threadsafe that are not used as task-related user exits, global user exits, or user-replaceable modules.