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How do I sleep for shorter than a second in Perl?

zengr
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ˈoʊ sɪks
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    It is because I believe this title is actually more helpful. Let me try to argument this. What B.D.F. did was duplicate the question in the title which adds no expressivity. When I was searching the web for the answer I actually looked for a millisecond sleep and not for a "shorter than a second" sleep. I say this version has a better chance of being hit through different google searches than B.D.F's one. Please correct me if I'm wrong. – ˈoʊ sɪks Jul 20 '09 at 13:52

6 Answers6

120

From the Perldoc page on sleep:

For delays of finer granularity than one second, the Time::HiRes module (from CPAN, and starting from Perl 5.8 part of the standard distribution) provides usleep().

Actually, it provides usleep() (which sleeps in microseconds) and nanosleep() (which sleeps in nanoseconds). You may want usleep(), which should let you deal with easier numbers. 1 millisecond sleep (using each):

use strict;
use warnings;

use Time::HiRes qw(usleep nanosleep);

# 1 millisecond == 1000 microseconds
usleep(1000);
# 1 microsecond == 1000 nanoseconds
nanosleep(1000000);

If you don't want to (or can't) load a module to do this, you may also be able to use the built-in select() function:

# Sleep for 250 milliseconds
select(undef, undef, undef, 0.25);
John Siracusa
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Chris Lutz
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    Caveat: although you could nanosleep(1), many OSes have some minimum granularity; e.g. I believe it's 1 ms in Windows XP, so you'd still sleep for a whole 1000000 ns there. – Piskvor left the building May 22 '09 at 08:56
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    The page on Time::HiRes says something like "if you need nanosleep(), you should reconsider whether or not Perl is the best tool for your job." – Chris Lutz May 22 '09 at 09:00
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    There is also Time::HiRes::sleep( 0.3 ) which will sleep for .3 of a second. – Peter N Lewis May 04 '11 at 03:32
39

Time::HiRes:

  use Time::HiRes;
  Time::HiRes::sleep(0.1); #.1 seconds
  Time::HiRes::usleep(1); # 1 microsecond.

http://perldoc.perl.org/Time/HiRes.html

Greg
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13

From perlfaq8:

How can I sleep() or alarm() for under a second?

If you want finer granularity than the 1 second that the sleep() function provides, the easiest way is to use the select() function as documented in select in perlfunc. Try the Time::HiRes and the BSD::Itimer modules (available from CPAN, and starting from Perl 5.8 Time::HiRes is part of the standard distribution).

brian d foy
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7

Use Time::HiRes.

TML
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5

A quick googling on "perl high resolution timers" gave a reference to Time::HiRes. Maybe that it what you want.

JesperE
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4
system "sleep 0.1";

does the trick.

Baum mit Augen
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Tim Tian
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  • It actually worked for me (not elegant, but for debug purposes it seems to work). – PiotrK Sep 20 '18 at 07:43
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    not really perl, but helpfull if you don't want to install Time::HiRes but need some sleeps smaller than 1 second but **don't forget**, that spawning a shell for this takes time itself, so you can't count on accuracy! – Jimmy Koerting Nov 22 '20 at 11:49