Procedure Definition Language Statements › Exclusive Control › Primary Exclusive Control

Primary Exclusive Control

The dataview in the following example is an updateable dataview. (In all the examples that follow, 'FOR EACH DVW' can be a full FOR statement including WHERE and ORDERED BY clauses).

Example

FOR EACH DVW
        SET...
        SET...
ENDFOR

Each record is read and returned to the program one by one. Each record is read with primary exclusive control. At this point, the record is updated. While it is held under primary exclusive control, another task cannot simultaneously read the record with update intent.

Primary exclusive control is established when the record is selected as part of the set of requested records. Primary exclusive control is maintained until after the last statement in the construct before the ENDFOR. The important points to note in the above example are:

• The FOR statement is processing only one record of the set at any point in time.
• Only one record of the set that meets the FOR/WHERE/ORDERED BY criteria is under primary exclusive control at any point in time.
• Primary exclusive control begins when the record is read at the FOR statement and ends when the update is done just before the ENDFOR statement.
• Primary exclusive control also ends if a TRANSMIT or a CICS SYNCPOINT command is encountered.
• A record held under primary exclusive control by one task cannot by simultaneously read with update intent by another task.

Note: This description does not apply to sequential batch processing.