Serializing with non-ISPF TSO and BATCH

ISPF relies on MVS™ allocation to serialize access to resources with concurrent batch or non-ISPF TSO users. ISPF uses dynamic allocation and allocates partitioned data sets with DISP=SHR before any ISPF generated ENQUEUE. To ensure integrity when batch or TSO users are not using ISPF services, if you are updating a data set, you must allocate the data set with DISP=OLD.

Note: ISPF's allocation with DISP=SHR causes MVS allocation to issue a shared ENQUEUE on Qname SYSDSN as follows:

     ENQ SYSDSN,dsname,S,44,SYSTEM

Non-ISPF TSO and Batch allocation with DISP=OLD causes MVS allocation to issue an exclusive ENQUEUE on Qname SYSDSN as follows:

     ENQ SYSDSN,dsname,E,44,SYSTEM

ISPF also issues ENQ, DEQ, and RESERVE macro instructions to serialize access to resources among multiple ISPF users. It is possible for the LMMOVE service or option 3.3 Move function to be used such that each of 2 users is holding a RESERVE (therefore an exclusive ENQ is held) that is being waited on by the other user. This occurs when the user 1 is moving from data set A to data set B, while at the same time, user 2 is moving from data set B to data set A. Each user holds a reserve on the output data set for the move and is requesting a reserve on the input for purposes of deleting the moved member. If this situation occurs, cancel one user off TSO, log back on, and reissue the move request.