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Class type Uq_engines.engine

class type ['t] engine = object .. end

This class type defines the interface an engine must support. The class parameter 't is the type of the result values (when the engine goes to state `Done).

Requirements for engines

method state : 't engine_state

Returns the state of the engine

method abort : unit -> unit

Forces that the engine aborts operation. If the state is already `Done , `Aborted, or `Error, this method must do nothing (you cannot abort an already finished engine).

method request_notification : (unit -> bool) -> unit

Requests notification about state changes.

After the notification has been requested, the passed function must be called whenever state changes its value (or might change its value; it is allowed to call the notification function more frequently than necessary). The function returns true if there is still interest in notification, and false if notification must be disabled; the function must not be called any longer in this case.

There can be any number of parallel active notifications. It is allowed that a notification callback function requests further notifications.

If the callback raises an exception, this exception is propagated to the caller of

method request_proxy_notification : ('t engine -> bool) -> unit

Requests to call back the function when there is another engine that can be used as proxy for this object. Note that this is a pure optimization for qseq_engine, and is normally not implemented for any other engine construction. It is ok to define this method as a no-op.

method event_system : Unixqueue.event_system

Returns the event system the engine is attached to

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