Shared-update processing

ISAM files can be opened and updated concurrently by several jobs. Each such job must activate shared-update processing in the corresponding FILE/FCB macro or ADD-FILE LINK command (SHARUPD=YES or SHARED-UPDATE=*YES, as appropriate). Data consistency is assured by the use of internal locks.
The user can also explicitly lock records by means of the ISAM key. In the macros GET, GETRL, GETKY and GETR the lock is requested by means of the LOCK operand. If the desired lock cannot be imposed because the record or range is already locked by another job, the job requesting the lock is entered in a queue (unless the program contains a routine (EXLST exit PGLOCK) which is activated when a page-lock event occurs).