108 lines
2.5 KiB
Prolog
108 lines
2.5 KiB
Prolog
/*************************************************************************
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* *
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* YAP Prolog *
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* *
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* Yap Prolog was developed at NCCUP - Universidade do Porto *
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* *
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* Copyright L.Damas, V.S.Costa and Universidade do Porto 1985-1997 *
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* *
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**************************************************************************
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* *
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* File: timeout.yap *
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* Last rev: 5/12/99 *
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* mods: *
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* comments: Goal within timeout *
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* *
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*************************************************************************/
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/**
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* @file timeout.yap
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* @author VITOR SANTOS COSTA <vsc@VITORs-MBP.lan>
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* @date Wed Nov 18 01:26:14 2015
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*
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* @brief Calls With Timeout
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*
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*
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*/
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:- module(timeout, [
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time_out/3
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]).
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/** @defgroup timeout Calls With Timeout
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@ingroup library
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@{
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The <tt>time_out/3</tt> command relies on the <tt>alarm/3</tt> built-in to
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implement a call with a maximum time of execution. The command is
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available with the `use_module(library(timeout))` command.
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@pred time_out(+ _Goal_, + _Timeout_, - _Result_)
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Execute goal _Goal_ with time limited _Timeout_, where
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_Timeout_ is measured in milliseconds. If the goal succeeds, unify
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_Result_ with success. If the timer expires before the goal
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terminates, unify _Result_ with <tt>time_out</tt>.
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This command is implemented by activating an alarm at procedure
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entry. If the timer expires before the goal completes, the alarm will
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throw an exception _timeout_.
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One should note that time_out/3 is not reentrant, that is, a goal
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called from `time_out` should never itself call
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time_out/3. Moreover, time_out/3 will deactivate any previous
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alarms set by alarm/3 and vice-versa, hence only one of these
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calls should be used in a program.
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Last, even though the timer is set in milliseconds, the current
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implementation relies on <tt>alarm/3</tt>, and therefore can only offer
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precision on the scale of seconds.
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*/
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:- meta_predicate time_out(0,+,-).
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:- use_module(library(hacks), [
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virtual_alarm/3
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]).
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%
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% not the nicest program I've ever seen.
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%
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time_out(Goal, Time, Result) :-
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T is Time//1000,
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UT is (Time mod 1000)*1000,
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catch( ( Result0 = success,
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setup_call_cleanup(
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virtual_alarm(T.UT,throw(time_out),_),
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Goal,
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virtual_alarm(0,_,RT)),
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( var(RT)
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-> virtual_alarm(0,_,_),
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(
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true
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;
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virtual_alarm(T.UT,throw(time_out),_),
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fail
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)
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; true
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)
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),
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time_out,
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Result0 = time_out ),
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Result = Result0.
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%% @}
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