event_enable(+EventHandle)

EventHandle

An event handle

Description

The given event is (re-)enabled. Since events are enabled by default, this only makes sense if the event had been previously disabled.

A disabled events behaves as if its handler was the goal 'true':

• Retrieving the goal using event_retrieve/3 returns 'true'
• When the event is raised (e.g. posted via event/1), nothing happens
• If the event gets disabled after it was raised, but before its handler execution has started, handler execution will be suppressed.

Note that disabling and enabling events are nonlogical operations which are not undone on backtracking.

Modes and Determinism

• event_enable(+) is det

Exceptions

(4) instantiation fault

EventHandle is un-instantiated

(5) type error

EventHandle is not a handle

Examples

    ?- event_create(writeln(hello), [], E),
       event_disable(E), writeln(disabled),
       event(E),	% does nothing
       event_enable(E), writeln(enabled),
       event(E).
    disabled
    enabled
    hello
    

See Also