Perl 5 version 8.0 documentation



Time::HiRes - High resolution alarm, sleep, gettimeofday, interval timers


  1. use Time::HiRes qw( usleep ualarm gettimeofday tv_interval );
  2. usleep ($microseconds);
  3. ualarm ($microseconds);
  4. ualarm ($microseconds, $interval_microseconds);
  5. $t0 = [gettimeofday];
  6. ($seconds, $microseconds) = gettimeofday;
  7. $elapsed = tv_interval ( $t0, [$seconds, $microseconds]);
  8. $elapsed = tv_interval ( $t0, [gettimeofday]);
  9. $elapsed = tv_interval ( $t0 );
  10. use Time::HiRes qw ( time alarm sleep );
  11. $now_fractions = time;
  12. sleep ($floating_seconds);
  13. alarm ($floating_seconds);
  14. alarm ($floating_seconds, $floating_interval);
  15. use Time::HiRes qw( setitimer getitimer
  17. setitimer ($which, $floating_seconds, $floating_interval );
  18. getitimer ($which);


The Time::HiRes module implements a Perl interface to the usleep, ualarm, gettimeofday, and setitimer/getitimer system calls. See the EXAMPLES section below and the test scripts for usage; see your system documentation for the description of the underlying usleep, ualarm, gettimeofday, and setitimer/getitimer calls.

If your system lacks gettimeofday(2) or an emulation of it you don't get gettimeofday() or the one-arg form of tv_interval(). If you don't have usleep(3) or select(2) you don't get usleep() or sleep(). If your system don't have ualarm(3) or setitimer(2) you don't get ualarm() or alarm(). If you try to import an unimplemented function in the use statement it will fail at compile time.

The following functions can be imported from this module. No functions are exported by default.

  • gettimeofday ()

    In array context returns a 2 element array with the seconds and microseconds since the epoch. In scalar context returns floating seconds like Time::HiRes::time() (see below).

  • usleep ( $useconds )

    Sleeps for the number of microseconds specified. Returns the number of microseconds actually slept. Can sleep for more than one second unlike the usleep system call. See also Time::HiRes::sleep() below.

  • ualarm ( $useconds [, $interval_useconds ] )

    Issues a ualarm call; interval_useconds is optional and will be 0 if unspecified, resulting in alarm-like behaviour.

  • tv_interval

    tv_interval ( $ref_to_gettimeofday [, $ref_to_later_gettimeofday] )

    Returns the floating seconds between the two times, which should have been returned by gettimeofday(). If the second argument is omitted, then the current time is used.

  • time ()

    Returns a floating seconds since the epoch. This function can be imported, resulting in a nice drop-in replacement for the time provided with core Perl, see the EXAMPLES below.

    NOTE 1: this higher resolution timer can return values either less or more than the core time(), depending on whether your platforms rounds the higher resolution timer values up, down, or to the nearest to get the core time(), but naturally the difference should be never more than half a second.

    NOTE 2: Since Sunday, September 9th, 2001 at 01:46:40 AM GMT (when the time() seconds since epoch rolled over to 1_000_000_000), the default floating point format of Perl and the seconds since epoch have conspired to produce an apparent bug: if you print the value of Time::HiRes::time() you seem to be getting only five decimals, not six as promised (microseconds). Not to worry, the microseconds are there (assuming your platform supports such granularity). What is going on is that the default floating point format of Perl only outputs 15 digits. In this case that means ten digits before the decimal separator and five after. To see the microseconds you can use either printf/sprintf with %.6f , or the gettimeofday() function in list context, which will give you the seconds and microseconds as two separate values.

  • sleep ( $floating_seconds )

    Sleeps for the specified amount of seconds. Returns the number of seconds actually slept (a floating point value). This function can be imported, resulting in a nice drop-in replacement for the sleep provided with perl, see the EXAMPLES below.

  • alarm ( $floating_seconds [, $interval_floating_seconds ] )

    The SIGALRM signal is sent after the specfified number of seconds. Implemented using ualarm(). The $interval_floating_seconds argument is optional and will be 0 if unspecified, resulting in alarm()-like behaviour. This function can be imported, resulting in a nice drop-in replacement for the alarm provided with perl, see the EXAMPLES below.

  • setitimer

    setitimer ( $which, $floating_seconds [, $interval_floating_seconds ] )

    Start up an interval timer: after a certain time, a signal arrives, and more signals may keep arriving at certain intervals. To disable a timer, use time of zero. If interval is set to zero (or unspecified), the timer is disabled after the next delivered signal.

    Use of interval timers may interfere with alarm(), sleep(), and usleep(). In standard-speak the "interaction is unspecified", which means that anything may happen: it may work, it may not.

    In scalar context, the remaining time in the timer is returned.

    In list context, both the remaining time and the interval are returned.

    There are three interval timers: the $which can be ITIMER_REAL, ITIMER_VIRTUAL, or ITIMER_PROF.

    ITIMER_REAL results in alarm()-like behavior. Time is counted in real time, that is, wallclock time. SIGALRM is delivered when the timer expires.

    ITIMER_VIRTUAL counts time in (process) virtual time, that is, only when the process is running. In multiprocessor/user/CPU systems this may be more or less than real or wallclock time. (This time is also known as the user time.) SIGVTALRM is delivered when the timer expires.

    ITIMER_PROF counts time when either the process virtual time or when the operating system is running on behalf of the process (such as I/O). (This time is also known as the system time.) (Collectively these times are also known as the CPU time.) SIGPROF is delivered when the timer expires. SIGPROF can interrupt system calls.

    The semantics of interval timers for multithreaded programs are system-specific, and some systems may support additional interval timers. See your setitimer() documentation.

  • getitimer ( $which )

    Return the remaining time in the interval timer specified by $which.

    In scalar context, the remaining time is returned.

    In list context, both the remaining time and the interval are returned. The interval is always what you put in using setitimer().


  1. use Time::HiRes qw(usleep ualarm gettimeofday tv_interval);
  2. $microseconds = 750_000;
  3. usleep $microseconds;
  4. # signal alarm in 2.5s & every .1s thereafter
  5. ualarm 2_500_000, 100_000;
  6. # get seconds and microseconds since the epoch
  7. ($s, $usec) = gettimeofday;
  8. # measure elapsed time
  9. # (could also do by subtracting 2 gettimeofday return values)
  10. $t0 = [gettimeofday];
  11. # do bunch of stuff here
  12. $t1 = [gettimeofday];
  13. # do more stuff here
  14. $t0_t1 = tv_interval $t0, $t1;
  15. $elapsed = tv_interval ($t0, [gettimeofday]);
  16. $elapsed = tv_interval ($t0); # equivalent code
  17. #
  18. # replacements for time, alarm and sleep that know about
  19. # floating seconds
  20. #
  21. use Time::HiRes;
  22. $now_fractions = Time::HiRes::time;
  23. Time::HiRes::sleep (2.5);
  24. Time::HiRes::alarm (10.6666666);
  25. use Time::HiRes qw ( time alarm sleep );
  26. $now_fractions = time;
  27. sleep (2.5);
  28. alarm (10.6666666);
  29. # Arm an interval timer to go off first at 10 seconds and
  30. # after that every 2.5 seconds, in process virtual time
  31. use Time::HiRes qw ( setitimer ITIMER_VIRTUAL time );
  32. $SIG{VTLARM} = sub { print time, "\n" };
  33. setitimer(ITIMER_VIRTUAL, 10, 2.5);


In addition to the perl API described above, a C API is available for extension writers. The following C functions are available in the modglobal hash:

  1. name C prototype
  2. --------------- ----------------------
  3. Time::NVtime double (*)()
  4. Time::U2time void (*)(UV ret[2])

Both functions return equivalent information (like gettimeofday ) but with different representations. The names NVtime and U2time were selected mainly because they are operating system independent. (gettimeofday is Un*x-centric.)

Here is an example of using NVtime from C:

  1. double (*myNVtime)();
  2. SV **svp = hv_fetch(PL_modglobal, "Time::NVtime", 12, 0);
  3. if (!svp) croak("Time::HiRes is required");
  4. if (!SvIOK(*svp)) croak("Time::NVtime isn't a function pointer");
  5. myNVtime = INT2PTR(double(*)(), SvIV(*svp));
  6. printf("The current time is: %f\n", (*myNVtime)());


Notice that the core time() maybe rounding rather than truncating. What this means that the core time() may be giving time one second later than gettimeofday(), also known as Time::HiRes::time().


D. Wegscheid <> R. Schertler <> J. Hietaniemi <> G. Aas <>


$Id:,v 1.20 1999/03/16 02:26:13 wegscd Exp $

$Log:,v $ Revision 1.20 1999/03/16 02:26:13 wegscd Add documentation for NVTime and U2Time.

Revision 1.19 1998/09/30 02:34:42 wegscd No changes, bump version.

Revision 1.18 1998/07/07 02:41:35 wegscd No changes, bump version.

Revision 1.17 1998/07/02 01:45:13 wegscd Bump version to 1.17

Revision 1.16 1997/11/13 02:06:36 wegscd version bump to accomodate HiRes.xs fix.

Revision 1.15 1997/11/11 02:17:59 wegscd POD editing, courtesy of Gisle Aas.

Revision 1.14 1997/11/06 03:14:35 wegscd Update version # for Makefile.PL and HiRes.xs changes.

Revision 1.13 1997/11/05 05:36:25 wegscd change version # for and HiRes.xs changes.

Revision 1.12 1997/10/13 20:55:33 wegscd Force a new version for Makefile.PL changes.

Revision 1.11 1997/09/05 19:59:33 wegscd New version to bump version for README and Makefile.PL fixes. Fix bad RCS log.

Revision 1.10 1997/05/23 01:11:38 wegscd Conditional compilation; EXPORT_FAIL fixes.

Revision 1.2 1996/12/30 13:28:40 wegscd Update documentation for what to do when missing ualarm() and friends.

Revision 1.1 1996/10/17 20:53:31 wegscd Fix =head1 being next to __END__ so pod2man works

Revision 1.0 1996/09/03 18:25:15 wegscd Initial revision


Copyright (c) 1996-1997 Douglas E. Wegscheid. All rights reserved. This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.