1/*  Part of SWI-Prolog
    2
    3    Author:        Jan Wielemaker
    4    E-mail:        J.Wielemaker@vu.nl
    5    WWW:           http://www.swi-prolog.org
    6    Copyright (c)  2010-2019, University of Amsterdam
    7			      CWI, Amsterdam
    8    All rights reserved.
    9
   10    Redistribution and use in source and binary forms, with or without
   11    modification, are permitted provided that the following conditions
   12    are met:
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   14    1. Redistributions of source code must retain the above copyright
   15       notice, this list of conditions and the following disclaimer.
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   17    2. Redistributions in binary form must reproduce the above copyright
   18       notice, this list of conditions and the following disclaimer in
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   23    "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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   34*/
   35
   36:- module(timeout,
   37	  [ time_out/3			% :Goal, +Time, -Result
   38	  ]).   39:- use_module(library(time)).

   49:- meta_predicate
   50    time_out(0, +, -).

 time_out(:Goal, +Time_ms, -Result) is nondet

This library provides a SICStus compatible implementation of time-outs. This predicate runs Goal as call/1 and binds Result to either success (the answer was produced within Time_ms) or time_out (Goal did not terminate within Time_ms). If Goal succeeds with a choice point, backtracking into it re-applies the time limit, i.e., each solution gets a Time_ms time limit.

Calls to time_out/3 can be nested. If an outer time out is triggered first, the inner time out is cancelled using a time_out(Id) exception and the outer one binds Result to time_out.

See also

- alarm/3, call_with_time_limit/2, call_with_inference_limit/3 and thread-based primitives such as thread_signal/2 and first_solution/3.

bug

- Unfortunately, our emulation is not fully compatible with the SICStus original. Notably, Time is measured in wall-time instead of virtual CPU time. Virtual CPU time is hard in threaded-environments. On most systems, you probably need a thread that measures the CPU usage of the monitored thread.

   76time_out(Goal, Time_ms, Result) :-
   77    Time_s is (Time_ms//1)/1000,
   78    prolog_current_frame(Fid),                  % Unique id for this call.
   79    catch( ( Result0 = success,
   80             setup_call_cleanup(
   81                 alarm(Time_s, throw(time_out(Fid)), Id),
   82                 Goal,
   83                 ( Removed = true, remove_alarm(Id) )),
   84             (   var(Removed)
   85             ->  uninstall_alarm(Id),
   86                 ( true ; install_alarm(Id,Time_s), fail )
   87             ;   true
   88             )
   89           ),
   90           time_out(Fid),
   91           Result0 = time_out ),
   92    Result = Result0