UNSUBSCRIBE statement

Cancels a subscription to an ABL named event. Specifically, the UNSUBSCRIBE statement cancels one or more subscriptions to one or more named events.

Syntax

UNSUBSCRIBE [ PROCEDURE subscriber-handle ]
  [ TO ] { event-name | ALL } [ IN publisher-handle ]

PROCEDURE subscriber-handle

A procedure handle representing the subscriber to a named event.

The PROCEDURE option lets one procedure cancel a subscription on behalf of another. For example, if you want procedure A to cancel a subscription on behalf of procedure B, set subscriber-handle to the procedure handle of B.

If the PROCEDURE option does not appear, the AVM assumes that the subscriber is THIS-PROCEDURE, the procedure that contains the UNSUBSCRIBE statement.

event-name

A quoted string or character expression representing the name of a named event.

ALL

Cancels all subscriptions.

IN publisher-handle

A procedure handle representing the publisher of a named event.

If the IN option appears, the AVM cancels subscriptions to named events published by publisher-handle-specifically, either all subscriptions (if the ALL option appears), or only subscriptions to event-name (if event-name appears).

If the IN option does not appear, the AVM cancels subscriptions regardless of the publisher-specifically, either all subscriptions (if the ALL option appears), or only subscriptions to event-name (if event-name appears).

Example

For an example, see the reference entry for the PUBLISH statement.

Notes

• When the AVM executes an UNSUBSCRIBE statement, it cancels a subscription when it finds a match. A match means that the SUBSCRIBE and UNSUBSCRIBE event names match, and that one of the following is true:
  • The subscription was created using SUBSCRIBE IN, cancelled using UNSUBSCRIBE IN, and the publisher and subscriber handles in the SUBSCRIBE and UNSUBSCRIBE statements match.
  • The subscription was created using SUBSCRIBE ANYWHERE, and cancelled using UNSUBSCRIBE without the IN option.
• The AVM executes the UNSUBSCRIBE statement with an implicit NO-ERROR option. That is, if the AVM cannot find a match, it does not report an error. To find out what errors, if any, occurred, use the ERROR-STATUS system handle.
• If you create a subscription using SUBSCRIBE ANYWHERE, you cannot cancel the subscription using UNSUBSCRIBE IN.

See also

PUBLISH statement, PUBLISHED-EVENTS attribute, SUBSCRIBE statement, Unsubscribe( ) event method