Explicit enqueuing (by the application programmer)

CICS provides enqueuing commands that can be useful in applications when you want to protect data and prevent transaction deadlocks.

CICS® provides the following explicit enqueuing commands:

EXEC CICS ENQ RESOURCE
EXEC CICS DEQ RESOURCE

You can use these commands to perform the following functions:

Protect data written into the common work area (CWA), which is not automatically protected by CICS
Prevent transaction deadlock by enqueuing on records that might be updated by more than one task concurrently
Protect a temporary storage queue from being read and updated concurrently.

To be effective, however, all transactions must adhere to the same convention. A transaction that accesses the CWA without using the agreed ENQ and DEQ commands is not suspended, and protection is violated.

After a task has issued an ENQ RESOURCE(data-area) command, any other task that issues an ENQ RESOURCE command with the same data-area parameter is suspended until the task issues a matching DEQ RESOURCE(data-area) command, or until the unit of work ends.

Note: Enqueueing on more than one resource concurrently might create a deadlock between transactions.