ADDRESS PPQ Commands › PPQ Operations Commands › LOCK Command

LOCK Command

The LOCK command prevents access to a queue by REXX programs other than the current one. It provides a means for handling problems that can arise from the multiple access situations created by the multitasking environment. Using LOCK is necessary only when you are writing multiple items that must be sequential in the queue.

This command has the following format:

ADDRESS PPQ 'LOCK QUEUE(qname) [WAIT(NO|YES|waittime)]'

QUEUE

Specifies the 1- to 16-character name of the queue (qname). The queue name can contain alphanumeric characters and any of these special characters: ! @ # $ _

The queue name cannot contain blanks.

WAIT

(Optional) Specifies what the command does if it cannot execute immediately. For example, the queue may be in use or locked by another REXX program. Valid WAIT values are:

NO

Returns a nonzero return code (RC) value immediately. For information about what happens when a command does not execute successfully, see the chapter on using program-to-program queues in the Administrator Guide.

YES

Waits indefinitely while blocking the current REXX program until the queue becomes available.

waittime

Specifies the number of seconds to wait (up to 100000) while blocking the current REXX program. Fractional values (such as 1.5) are valid.

Default: NO

Usage Notes:

• Unlock a queue with the UNLOCK command as soon as possible after you lock it to prevent unnecessary delays in other REXX programs.
• Locks are nested. For every LOCK command issued for a queue, an equal number of UNLOCK commands are required to completely remove the lock. Be sure that each LOCK command in your REXX program has a corresponding UNLOCK command.

  Note: You can retrieve the lock nesting count using the LIST command.

• When a queue is in use by another REXX program, the LOCK command does not take effect until the current operation has completed. If the delay is prolonged or if the queue is locked by another REXX program, the LOCK command waits for the amount of time specified by the optional WAIT operand.
• You can lock a remote queue.
• It is good programming practice for user-written programs to eventually unlock every queue that they have locked.