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time.pl
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time.pl
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/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Written 2020-2023 by Markus Triska (triska@metalevel.at)
Part of Scryer Prolog.
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
/** This library provides predicates for reasoning about time.
*/
:- module(time, [max_sleep_time/1, sleep/1, time/1, current_time/1, format_time//2]).
:- use_module(library(format)).
:- use_module(library(iso_ext)).
:- use_module(library(error)).
:- use_module(library(dcgs)).
:- use_module(library(lists)).
:- use_module(library(charsio), [read_from_chars/2]).
%% current_time(-T)
%
% Yields the current system time _T_ in an opaque form, called a
% _time stamp_. Use `format_time//2` to describe strings that contain
% attributes of the time stamp.
current_time(T) :-
'$current_time'(T0),
read_from_chars(T0, T).
%% format_time(FormatString, TimeStamp)//
%
% The nonterminal format_time//2 describes a list of characters that
% are formatted according to a format string. Usage:
%
% ```
% phrase(format_time(FormatString, TimeStamp), Cs)
% ```
%
% TimeStamp represents a moment in time in an opaque form, as for
% example obtained by `current_time/1`.
%
% FormatString is a list of characters that are interpreted literally,
% except for the following specifiers (and possibly more in the future):
%
% | `%Y` | year of the time stamp. Example: 2020. |
% | `%m` | month number (01-12), zero-padded to 2 digits |
% | `%d` | day number (01-31), zero-padded to 2 digits |
% | `%H` | hour number (00-24), zero-padded to 2 digits |
% | `%M` | minute number (00-59), zero-padded to 2 digits |
% | `%S` | second number (00-60), zero-padded to 2 digits |
% | `%b` | abbreviated month name, always 3 letters |
% | `%a` | abbreviated weekday name, always 3 letters |
% | `%A` | full weekday name |
% | `%j` | day of the year (001-366), zero-padded to 3 digits |
% | `%%` | the literal `%` |
%
% Example:
%
% ```
% ?- current_time(T), phrase(format_time("%d.%m.%Y (%H:%M:%S)", T), Cs).
% T = [...], Cs = "11.06.2020 (00:24:32)".
% ```
format_time([], _) --> [].
format_time(['%','%'|Fs], T) --> !, "%", format_time(Fs, T).
format_time(['%',Spec|Fs], T) --> !,
( { member(Spec=Value, T) } ->
seq(Value)
; { domain_error(time_specifier, Spec, format_time//2) }
),
format_time(Fs, T).
format_time([F|Fs], T) --> [F], format_time(Fs, T).
%% max_sleep_time(T)
%
% The maximum admissible time span for `sleep/1`.
max_sleep_time(0xfffffffffffffbff).
%% sleep(S)
%
% Sleeps for S seconds (a floating point number or integer).
sleep(T) :-
builtins:must_be_number(T, sleep),
( T < 0 ->
domain_error(not_less_than_zero, T, sleep/1)
; max_sleep_time(N), T > N ->
throw(error(representation_error(max_sleep_time), sleep/1))
; '$sleep'(T)
).
% '$cpu_now' can be replaced by statistics/2 once that is implemented.
:- meta_predicate time(0).
:- dynamic(time_id/1).
:- dynamic(time_state/2).
time_next_id(N) :-
( retract(time_id(N0)) ->
N is N0 + 1
; N = 0
),
asserta(time_id(N)).
%% time(Goal)
%
% Reports the execution time of Goal.
time(Goal) :-
'$cpu_now'(T0),
time_next_id(ID),
setup_call_cleanup(asserta(time_state(ID, T0)),
( call_cleanup(catch(Goal, E, (report_time(ID),throw(E))),
Det = true),
time_true(ID),
( Det == true -> !
; true
)
; report_time(ID),
false
),
retract(time_state(ID, _))).
time_true(ID) :-
report_time(ID).
time_true(ID) :-
% on backtracking, update the stored CPU time for this ID
retract(time_state(ID, _)),
'$cpu_now'(T0),
asserta(time_state(ID, T0)),
false.
report_time(ID) :-
time_state(ID, T0),
'$cpu_now'(T),
Time is T - T0,
( bb_get('$answer_count', 0) ->
Pre = " ", Post = ""
; Pre = "", Post = " "
),
format("~s% CPU time: ~3fs~n~s", [Pre,Time,Post]).
/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
?- time((true;false)).
%@ % CPU time: 0.006s
%@ true
%@ ; % CPU time: 0.001s
%@ false.
:- time(use_module(library(clpz))).
%@ % CPU time: 3.711s
%@ true.
:- time(use_module(library(lists))).
%@ % CPU time: 0.006s
%@ true.
?- time(member(X, "abc")).
%@ % CPU time: 0.005s
%@ X = a
%@ ; % CPU time: 0.000s
%@ X = b
%@ ; % CPU time: 0.000s
%@ X = c
%@ ; % CPU time: 0.000s
%@ false.
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */