Lock requests can be conditional or unconditional. When you issue a conditional lock request (LOCKMODE=COND), your program regains control either with or without the lock request being satisfied. If the lock request could not be processed, your request simply fails.

When you issue an unconditional lock request (LOCKMODE=UNCOND), your program regains control only when the lock request has been processed successfully. If the request cannot be satisfied immediately, it is queued until it can be satisfied. Note that only the SET and NOTHELD requests give you an explicit choice of conditional or unconditional processing (using the LOCKMODE parameter.) Other requests might always be conditional, always unconditional, or either depending on the other parameters specified (for example, the RESET request is always conditional when LOCKCOMP is specified and always unconditional when LOCKCOMP is omitted.)