time.pl

/*  Part of SWI-Prolog

    Author:        Jan Wielemaker
    E-mail:        J.Wielemaker@vu.nl
    WWW:           http://www.swi-prolog.org
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                              VU University Amsterdam
                              CWI, Amsterdam
                              SWI-Prolog Solutions b.v.
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*/

:- module(time,
          [ alarm/3,                    % +Time, :Callable, -Id
            alarm/4,                    % +Time, :Callable, -Id, +Options
            alarm_at/3,                 % +Time, :Callable, -Id
            alarm_at/4,                 % +Time, :Callable, -Id, +Options
            remove_alarm/1,             % +Id
            install_alarm/1,            % +Id
            install_alarm/2,            % +Id, +Time
            uninstall_alarm/1,          % +Id
            current_alarm/4,            % ?At, ?:Goal, ?Id, ?Status
            call_with_time_limit/2,     % +Time, :Callable
            call_with_time_limit/3      % +Time, :Callable, +Context
          ]).
:- autoload(library(lists),[member/2]).

:- set_prolog_flag(generate_debug_info, false).

:- meta_predicate
    call_with_time_limit(+, 0),
    call_with_time_limit(+, 0, +),
    alarm(+, 0, -),
    alarm(+, 0, -, +),
    alarm_at(+, 0, -, +),
    current_alarm(?, :, ?, ?).

:- predicate_options(alarm/4, 4,
                     [ remove(boolean),
                       install(boolean)
                     ]).


/** <module> Time and alarm library

The library(time) provides timing and alarm functions. Alarms are
thread-specific, i.e., creating an alarm causes the alarm goal to be
called in the thread that created it. The predicate current_alarm/4 only
reports alarms that are related to the calling thread. If a thread
terminates, all remaining alarms are silently removed. Most applications
use call_with_time_limit/2.
*/

%!  alarm(+Time, :Callable, -Id) is det.
%!  alarm(+Time, :Callable, -Id, +Options) is det.
%
%   Set up an alarm to be  signaled   Time  seconds from now. If the
%   alarm expires, Callable is called   asynchronously. Callable can
%   be used to raise  an  exception   using  throw/1  to  abort some
%   execution.
%
%   Options is a list of Name(Value) options.  Currently defined
%   options are:
%
%           * remove(Bool)
%           If =true= (default =false=), remove the alarm-event (as
%           remove_alarm/1) after it has been fired.
%           * install(Bool)
%           If =false= (default =true=) do not install the alarm.
%           It must be installed separately using install_alarm/1.

%!  alarm_at(+Time, :Callable, -Id) is det.
%!  alarm_at(+Time, :Callable, -Id, +Options) is det.
%
%   As alarm/3 and alarm/4, but schedule   the  alarm at an absolute
%   point in time.
%
%   @see date_time_stamp/2.

%!  install_alarm(+Id) is det.
%!  install_alarm(+Id, +RelTime) is det.
%
%   Install an alarm allocated using alarm/4 with the install(false)
%   option or de-activated using  uninstall_alarm/1.   With  a given
%   RelTime, the alarm  is  scheduled  at   the  RelTime  from  now.
%   Otherwise it is scheduled on the   same (absolute) time on which
%   is was created.

%!  uninstall_alarm(+Id) is det.
%
%   De-activate an alarm. This does _not_ invalidate Id, but ensures
%   that the alarm will not fire. The alarm can be rescheduled to
%   the original time using install_alarm/1 or to a new time using
%   install_alarm/2.

%!  remove_alarm(+Id) is det.
%
%   Remove an alarm.  If it has not yet been fired, it never will.

%!  current_alarm(?Time, :Goal, ?Id, ?Status) is nondet.
%
%   Enumerate the alarms in the schedule.  Time is the absolute time
%   the event is scheduled for (see   also  get_time/1). Goal is the
%   goal to execute,  Id  is  the   identifier  and  Status  is  the
%   scheduling status. It takes the value   =done=  if the alarm has
%   been fired, =next= if the event is   the next to be executed and
%   =scheduled= otherwise.

:- use_foreign_library(foreign(time)).
:- public time_debug/1.                 % set debugging

%!  call_with_time_limit(+Time, :Goal) is det.
%!  call_with_time_limit(+Time, :Goal, +Context) is det.
%
%   Call Goal, while watching out for a (wall-time) limit. If this limit
%   is  exceeded,  the  exception    `time_limit_exceeded`   is  raised.
%   call_with_time_limit/3 throws time_limit_exceeded(Context).  Goal is
%   called as in once/1.
%
%   @throws `time_limit_exceeded` (call_with_time_limit/2) or
%   time_limit_exceeded(Context) (call_with_time_limit/3).

call_with_time_limit(Time, Goal) :-
    call_with_time_limit(Time, Goal, '$no_ctx').

call_with_time_limit(Time, Goal, Ctx) :-
    Time > 0,
    !,
    setup_call_cleanup(alarm(Time, time_limit_exceeded(Time, Ctx),
                             Id, [install(false)]),
                       run_alarm_goal(Id, Goal),
                       remove_alarm_notrace(Id)).
call_with_time_limit(_Time, _Goal, _Ctx) :-
    throw(time_limit_exceeded).

run_alarm_goal(AlarmID, Goal) :-
    install_alarm(AlarmID),
    Goal,
    !.

time_limit_exceeded(_Time, Ctx) :-
    (   Ctx == '$no_ctx'
    ->  throw(time_limit_exceeded)
    ;   throw(time_limit_exceeded(Ctx))
    ).

current_alarm(Time, Goal, Id, Status) :-
    current_alarms(Time, Goal, Id, Status, List),
    member(alarm(Time, Goal, Id, Status), List).

                 /*******************************
                 *        HANDLE MESSAGES       *
                 *******************************/

:- multifile
    prolog:message/3.

prolog:message(time_limit_exceeded) -->
    [ 'Time limit exceeded' ].
prolog:message(time_limit_exceeded(Context)) -->
    [ 'Time limit exceeded: ~p'-[Context] ].

                 /*******************************
                 *             ALARM            *
                 *******************************/

:- multifile sandbox:safe_meta_predicate/1.

sandbox:safe_meta_predicate(time:call_with_time_limit/2).