ISPF GUI TSO line mode message queue enqueue

Running ISPF GUI with TSO line mode support (that is, displaying TSO line mode and tputs/tgets in the ISPF/TSO window) requires a messaging queue for each user (TSO address space). This is used to coordinate the incoming TSO line mode and TPUT/TGET messages so that they will be synchronized correctly. Thus, ISPF issues this enqueue before placing messages on or retrieving messages from this message queue:

      ENQ SYSZDTSK,rname,E,38,SYSTEMS

where

rname: 'ISPF/TSO_WINDOW_SERIALIZATION' followed by a 64 bit unique ID for the TSO address space

Note: In addition to issuing this enqueue while running in GUI mode, this enqueue on SYSZDTSK is issued from the ISPF SVC 93 exit ISPSC93X when processing a cross-memory message even if the user is not running in GUI mode. This is because at the point the enqueue must be issued, the exit is not running in the user's address space and therefore does not know if the user is running in ISPF GUI mode.