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ISGNQXIT — ISGENQ / ENQ / DEQ Installation Exit z/OS MVS Installation Exits SA23-1381-00 |
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For the best performance, IBM® recommends that the installation use the ISGNQXITFAST rather than ISGNQXIT. The ISGNQXIT exit should only be used if the ISGNQXITFAST exit cannot be used. In no case should both exits be used because both will be called on every ENQ resulting in degraded system performance. For each ISGENQ/ENQ/DEQ/RESERVE request with SCOPE=SYSTEM or SCOPE=SYSTEMS, the system invokes the ENQ/DEQ Installation Exit point, ISGNQXIT. The exit routines can modify attributes of the request prior to Resource Names List (RNL) processing. See z/OS MVS Planning: Global Resource Serialization in z/OS Internet Library at http://www.ibm.com/systems/z/os/zos/bkserv/ for the installation flow through ENQ/DEQ exits. By altering
the exit parameter list, the exit can:
Note: The exit routine cannot change the scope
nor UCB
address of a request when the program issues the ENQ or ISGENQ macro
with RNL=NO. The Nqxp_SF1_RnlEqNo bit passed in the parameter list
indicates if RNL=NO was specified.
This exit is invoked under the caller's unit of work on the system where the caller is running. For global resource requests, the exit is invoked only on the system where the request is made. Note:
Replacing the Exit RoutineUnlike RNL changes, GRS does not know how an exit alters the resource identity of a request. Therefore, to maintain data integrity, do not make an exit change that alters the resource identity of any outstanding or in-flight ENQ or DEQ requests. The resource identity consists of the QNAME, RNAME, SCOPE, and hardware reserve status. When you make exit changes, first stop the programs that are currently using the resource, and do not resume the programs until all the exit changes in the GRS complex have completed. Any changes the exit makes must be taken into consideration. For information regarding dynamic exit routine replacement, see Replacing a Dynamic Exit Routine. Exit Routine EnvironmentISGNQXIT
receives control in the following environment:
Exit Recovery is as follows.
Exit Routine ProcessingThe ISGNQXIT exit routine is invoked for every ENQ/DEQ/RESERVE/ISGENQ SCOPE=SYSTEM or SCOPE=SYSTEMS request issued for a resource. If any exit routines are defined to the dynamic exits facility, those routines are invoked before Resource Names List (RNL) processing. By
updating and using information in the parameter list, the exit routine
alters the following characteristics of the request:
The exit routine can also indicate that RNL processing can be bypassed. Programming ConsiderationsObserve the following conventions
when coding an ISGENQ,
ENQ, DEQ and RESERVE exit routine:
Entry SpecificationsThe ISGENQ/ENQ/DEQ/RESERVE mainline routine passes the address of the ENQ exit parameter list (ISGYNQXP). Registers at Entry: The contents of the registers on entry to the exit are as follows.
Parameter List Contents: Register 1 contains the address of the exit parameter (NQXP) that is mapped by macro ISGYNQXP. Refer to z/OS MVS Data Areas in z/OS Internet Library at http://www.ibm.com/systems/z/os/zos/bkserv/ for the mapping of the ISGYNQXP data area. Return SpecificationsThe ISGENQ/ENQ/DEQ installation exit sets the appropriate request flag and alters the value in the parameter list. For example, to change the major name, the exit sets Nqxp_RFI_ChangeQName to '1'b and Nqxp_CP_QNAME to the new major name. Registers at Exit: Upon return from the exit processing, the register contents must be as follows.
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