Time::HiRes(3perl) Perl Programmers Reference Guide Time::HiRes(3perl)
NAME
Time::HiRes - High resolution alarm, sleep, gettimeofday, interval
timers
SYNOPSIS
use Time::HiRes qw( usleep ualarm gettimeofday tv_interval nanosleep
clock_gettime clock_getres clock_nanosleep clock
stat lstat utime);
usleep ($microseconds);
nanosleep ($nanoseconds);
ualarm ($microseconds);
ualarm ($microseconds, $interval_microseconds);
$t0 = [gettimeofday];
($seconds, $microseconds) = gettimeofday;
$elapsed = tv_interval ( $t0, [$seconds, $microseconds]);
$elapsed = tv_interval ( $t0, [gettimeofday]);
$elapsed = tv_interval ( $t0 );
use Time::HiRes qw ( time alarm sleep );
$now_fractions = time;
sleep ($floating_seconds);
alarm ($floating_seconds);
alarm ($floating_seconds, $floating_interval);
use Time::HiRes qw( setitimer getitimer );
setitimer ($which, $floating_seconds, $floating_interval );
getitimer ($which);
use Time::HiRes qw( clock_gettime clock_getres clock_nanosleep
CLOCK_REALTIME ITIMER_REAL ITIMER_VIRTUAL ITIMER_PROF
ITIMER_REALPROF );
$realtime = clock_gettime(CLOCK_REALTIME);
$resolution = clock_getres(CLOCK_REALTIME);
clock_nanosleep(CLOCK_REALTIME, 1.5e9);
clock_nanosleep(CLOCK_REALTIME, time()*1e9 + 10e9, TIMER_ABSTIME);
my $ticktock = clock();
use Time::HiRes qw( stat lstat );
my @stat = stat("file");
my @stat = stat(FH);
my @stat = lstat("file");
use Time::HiRes qw( utime );
utime $floating_seconds, $floating_seconds, file...;
DESCRIPTION
The "Time::HiRes" module implements a Perl interface to the "usleep",
"nanosleep", "ualarm", "gettimeofday", and "setitimer"/"getitimer"
system calls, in other words, high resolution time and timers. See the
"EXAMPLES" section below and the test scripts for usage; see your system
documentation for the description of the underlying "nanosleep" or
"usleep", "ualarm", "gettimeofday", and "setitimer"/"getitimer" calls.
If your system lacks gettimeofday() or an emulation of it you don't get
gettimeofday() or the one-argument form of tv_interval(). If your
system lacks all of nanosleep(), usleep(), select(), and "poll", you
don't get Time::HiRes::usleep(), Time::HiRes::nanosleep(), or
Time::HiRes::sleep(). If your system lacks both ualarm() and
setitimer() you don't get Time::HiRes::ualarm() or Time::HiRes::alarm().
If you try to import an unimplemented function in the "use" statement it
will fail at compile time.
If your subsecond sleeping is implemented with nanosleep() instead of
usleep(), you can mix subsecond sleeping with signals since nanosleep()
does not use signals. This, however, is not portable, and you should
first check for the truth value of &Time::HiRes::d_nanosleep to see
whether you have nanosleep, and then carefully read your nanosleep() C
API documentation for any peculiarities.
If you are using "nanosleep" for something else than mixing sleeping
with signals, give some thought to whether Perl is the tool you should
be using for work requiring nanosecond accuracies.
Remember that unless you are working on a hard realtime system, any
clocks and timers will be imprecise, especially so if you are working in
a pre-emptive multiuser system. Understand the difference between
wallclock time and process time (in UNIX-like systems the sum of user
and system times). Any attempt to sleep for X seconds will most
probably end up sleeping more than that, but don't be surprised if you
end up sleeping slightly less.
The following functions can be imported from this module. No functions
are exported by default.
gettimeofday ()
In array context returns a two-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 (millionths of a second)
specified. Returns the number of microseconds actually slept. Can
sleep for more than one second, unlike the "usleep" system call.
Can also sleep for zero seconds, which often works like a thread
yield. See also Time::HiRes::sleep(), and clock_nanosleep().
Do not expect usleep() to be exact down to one microsecond.
nanosleep ( $nanoseconds )
Sleeps for the number of nanoseconds (1e9ths of a second) specified.
Returns the number of nanoseconds actually slept (accurate only to
microseconds, the nearest thousand of them). Can sleep for more
than one second. Can also sleep for zero seconds, which often works
like a thread yield. See also Time::HiRes::sleep(),
Time::HiRes::usleep(), and clock_nanosleep().
Do not expect nanosleep() to be exact down to one nanosecond.
Getting even accuracy of one thousand nanoseconds is good.
ualarm ( $useconds [, $interval_useconds ] )
Issues a "ualarm" call; the $interval_useconds is optional and will
be zero if unspecified, resulting in "alarm"-like behaviour.
Returns the remaining time in the alarm in microseconds, or "undef"
if an error occurred.
ualarm(0) will cancel an outstanding ualarm().
Note that the interaction between alarms and sleeps is unspecified.
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 platform
rounds the higher resolution timer values up, down, or to the
nearest second to get the core time(), but naturally the difference
should be never more than half a second. See also "clock_getres",
if available in your system.
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 in the first
place). 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.
Note that the interaction between alarms and sleeps is unspecified.
alarm ( $floating_seconds [, $interval_floating_seconds ] )
The "SIGALRM" signal is sent after the specified number of seconds.
Implemented using setitimer() if available, ualarm() if not. The
$interval_floating_seconds argument is optional and will be zero 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.
Returns the remaining time in the alarm in seconds, or "undef" if an
error occurred.
NOTE 1: With some combinations of operating systems and Perl
releases "SIGALRM" restarts select(), instead of interrupting it.
This means that an alarm() followed by a select() may together take
the sum of the times specified for the alarm() and the select(), not
just the time of the alarm().
Note that the interaction between alarms and sleeps is unspecified.
setitimer ( $which, $floating_seconds [, $interval_floating_seconds ] )
Start up an interval timer: after a certain time, a signal ($which)
arrives, and more signals may keep arriving at certain intervals.
To disable an "itimer", use $floating_seconds of zero. If the
$interval_floating_seconds 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 usually three or four interval timers (signals) available:
the $which can be "ITIMER_REAL", "ITIMER_VIRTUAL", "ITIMER_PROF", or
"ITIMER_REALPROF". Note that which ones are available depends: true
UNIX platforms usually have the first three, but only Solaris seems
to have "ITIMER_REALPROF" (which is used to profile multithreaded
programs). Win32 unfortunately does not have interval timers.
"ITIMER_REAL" results in alarm()-like behaviour. 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.) (The sum of
user time and system time is 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. For example, it is unspecified which thread gets the
signals. See your setitimer(2) 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().
clock_gettime ( $which )
Return as seconds the current value of the POSIX high resolution
timer specified by $which. All implementations that support POSIX
high resolution timers are supposed to support at least the $which
value of "CLOCK_REALTIME", which is supposed to return results close
to the results of "gettimeofday", or the number of seconds since
00:00:00:00 January 1, 1970 Greenwich Mean Time (GMT). Do not
assume that CLOCK_REALTIME is zero, it might be one, or something
else. Another potentially useful (but not available everywhere)
value is "CLOCK_MONOTONIC", which guarantees a monotonically
increasing time value (unlike time() or gettimeofday(), which can be
adjusted). See your system documentation for other possibly
supported values.
clock_getres ( $which )
Return as seconds the resolution of the POSIX high resolution timer
specified by $which. All implementations that support POSIX high
resolution timers are supposed to support at least the $which value
of "CLOCK_REALTIME", see "clock_gettime".
NOTE: the resolution returned may be highly optimistic. Even if the
resolution is high (a small number), all it means is that you'll be
able to specify the arguments to clock_gettime() and
clock_nanosleep() with that resolution. The system might not
actually be able to measure events at that resolution, and the
various overheads and the overall system load are certain to affect
any timings.
clock_nanosleep ( $which, $nanoseconds, $flags = 0)
Sleeps for the number of nanoseconds (1e9ths of a second) specified.
Returns the number of nanoseconds actually slept. The $which is the
"clock id", as with clock_gettime() and clock_getres(). The flags
default to zero but "TIMER_ABSTIME" can specified (must be exported
explicitly) which means that $nanoseconds is not a time interval (as
is the default) but instead an absolute time. Can sleep for more
than one second. Can also sleep for zero seconds, which often works
like a thread yield. See also Time::HiRes::sleep(),
Time::HiRes::usleep(), and Time::HiRes::nanosleep().
Do not expect clock_nanosleep() to be exact down to one nanosecond.
Getting even accuracy of one thousand nanoseconds is good.
clock()
Return as seconds the process time (user + system time) spent by the
process since the first call to clock() (the definition is not
"since the start of the process", though if you are lucky these
times may be quite close to each other, depending on the system).
What this means is that you probably need to store the result of
your first call to clock(), and subtract that value from the
following results of clock().
The time returned also includes the process times of the terminated
child processes for which wait() has been executed. This value is
somewhat like the second value returned by the times() of core Perl,
but not necessarily identical. Note that due to backward
compatibility limitations the returned value may wrap around at
about 2147 seconds or at about 36 minutes.
stat
stat FH
stat EXPR
lstat
lstat FH
lstat EXPR
As "stat" in perlfunc or "lstat" in perlfunc but with the
access/modify/change file timestamps in subsecond resolution, if the
operating system and the filesystem both support such timestamps.
To override the standard stat():
use Time::HiRes qw(stat);
Test for the value of &Time::HiRes::d_hires_stat to find out whether
the operating system supports subsecond file timestamps: a value
larger than zero means yes. There are unfortunately no easy ways to
find out whether the filesystem supports such timestamps. UNIX
filesystems often do; NTFS does; FAT doesn't (FAT timestamp
granularity is two seconds).
A zero return value of &Time::HiRes::d_hires_stat means that
Time::HiRes::stat is a no-op passthrough for CORE::stat() (and
likewise for lstat), and therefore the timestamps will stay
integers. The same thing will happen if the filesystem does not do
subsecond timestamps, even if the &Time::HiRes::d_hires_stat is non-
zero.
In any case do not expect nanosecond resolution, or even a
microsecond resolution. Also note that the modify/access timestamps
might have different resolutions, and that they need not be
synchronized, e.g. if the operations are
write
stat # t1
read
stat # t2
the access time stamp from t2 need not be greater-than the modify
time stamp from t1: it may be equal or less.
utime LIST
As "utime" in perlfunc but with the ability to set the access/modify
file timestamps in subsecond resolution, if the operating system and
the filesystem, and the mount options of the filesystem, all support
such timestamps.
To override the standard utime():
use Time::HiRes qw(utime);
Test for the value of &Time::HiRes::d_hires_utime to find out
whether the operating system supports setting subsecond file
timestamps.
As with CORE::utime(), passing undef as both the atime and mtime
will call the syscall with a NULL argument.
The actual achievable subsecond resolution depends on the
combination of the operating system and the filesystem.
Modifying the timestamps may not be possible at all: for example,
the "noatime" filesystem mount option may prohibit you from changing
the access time timestamp.
Returns the number of files successfully changed.
EXAMPLES
use Time::HiRes qw(usleep ualarm gettimeofday tv_interval);
$microseconds = 750_000;
usleep($microseconds);
# signal alarm in 2.5s & every .1s thereafter
ualarm(2_500_000, 100_000);
# cancel that ualarm
ualarm(0);
# get seconds and microseconds since the epoch
($s, $usec) = gettimeofday();
# measure elapsed time
# (could also do by subtracting 2 gettimeofday return values)
$t0 = [gettimeofday];
# do bunch of stuff here
$t1 = [gettimeofday];
# do more stuff here
$t0_t1 = tv_interval $t0, $t1;
$elapsed = tv_interval ($t0, [gettimeofday]);
$elapsed = tv_interval ($t0); # equivalent code
#
# replacements for time, alarm and sleep that know about
# floating seconds
#
use Time::HiRes;
$now_fractions = Time::HiRes::time;
Time::HiRes::sleep (2.5);
Time::HiRes::alarm (10.6666666);
use Time::HiRes qw ( time alarm sleep );
$now_fractions = time;
sleep (2.5);
alarm (10.6666666);
# Arm an interval timer to go off first at 10 seconds and
# after that every 2.5 seconds, in process virtual time
use Time::HiRes qw ( setitimer ITIMER_VIRTUAL time );
$SIG{VTALRM} = sub { print time, "\n" };
setitimer(ITIMER_VIRTUAL, 10, 2.5);
use Time::HiRes qw( clock_gettime clock_getres CLOCK_REALTIME );
# Read the POSIX high resolution timer.
my $high = clock_gettime(CLOCK_REALTIME);
# But how accurate we can be, really?
my $reso = clock_getres(CLOCK_REALTIME);
use Time::HiRes qw( clock_nanosleep TIMER_ABSTIME );
clock_nanosleep(CLOCK_REALTIME, 1e6);
clock_nanosleep(CLOCK_REALTIME, 2e9, TIMER_ABSTIME);
use Time::HiRes qw( clock );
my $clock0 = clock();
... # Do something.
my $clock1 = clock();
my $clockd = $clock1 - $clock0;
use Time::HiRes qw( stat );
my ($atime, $mtime, $ctime) = (stat("istics"))[8, 9, 10];
C API
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:
name C prototype
--------------- ----------------------
Time::NVtime NV (*)()
Time::U2time void (*)(pTHX_ 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 Unix-centric, though some platforms like Win32 and
VMS have emulations for it.)
Here is an example of using "NVtime" from C:
NV (*myNVtime)(); /* Returns -1 on failure. */
SV **svp = hv_fetchs(PL_modglobal, "Time::NVtime", 0);
if (!svp) croak("Time::HiRes is required");
if (!SvIOK(*svp)) croak("Time::NVtime isn't a function pointer");
myNVtime = INT2PTR(NV(*)(), SvIV(*svp));
printf("The current time is: %" NVff "\n", (*myNVtime)());
DIAGNOSTICS
useconds or interval more than ...
In ualarm() you tried to use number of microseconds or interval (also in
microseconds) more than 1_000_000 and setitimer() is not available in
your system to emulate that case.
negative time not invented yet
You tried to use a negative time argument.
internal error: useconds < 0 (unsigned ... signed ...)
Something went horribly wrong-- the number of microseconds that cannot
become negative just became negative. Maybe your compiler is broken?
useconds or uinterval equal to or more than 1000000
In some platforms it is not possible to get an alarm with subsecond
resolution and later than one second.
unimplemented in this platform
Some calls simply aren't available, real or emulated, on every platform.
CAVEATS
Notice that the core time() maybe rounding rather than truncating. What
this means is that the core time() may be reporting the time as one
second later than gettimeofday() and Time::HiRes::time().
Adjusting the system clock (either manually or by services like ntp) may
cause problems, especially for long running programs that assume a
monotonously increasing time (note that all platforms do not adjust time
as gracefully as UNIX ntp does). For example in Win32 (and derived
platforms like Cygwin and MinGW) the Time::HiRes::time() may temporarily
drift off from the system clock (and the original time()) by up to 0.5
seconds. Time::HiRes will notice this eventually and recalibrate. Note
that since Time::HiRes 1.77 the clock_gettime(CLOCK_MONOTONIC) might
help in this (in case your system supports CLOCK_MONOTONIC).
Some systems have APIs but not implementations: for example QNX and
Haiku have the interval timer APIs but not the functionality.
In pre-Sierra macOS (pre-10.12, OS X) clock_getres(), clock_gettime()
and clock_nanosleep() are emulated using the Mach timers; as a side
effect of being emulated the CLOCK_REALTIME and CLOCK_MONOTONIC are the
same timer.
gnukfreebsd seems to have non-functional futimens() and utimensat() (at
least as of 10.1): therefore the hires utime() does not work.
SEE ALSO
Perl modules BSD::Resource, Time::TAI64.
Your system documentation for clock(3), clock_gettime(2),
clock_getres(3), clock_nanosleep(3), clock_settime(2), getitimer(2),
gettimeofday(2), setitimer(2), sleep(3), stat(2), ualarm(3).
AUTHORS
D. Wegscheid <wegscd@whirlpool.com> R. Schertler <roderick@argon.org> J.
Hietaniemi <jhi@iki.fi> G. Aas <gisle@aas.no>
COPYRIGHT AND LICENSE
Copyright (c) 1996-2002 Douglas E. Wegscheid. All rights reserved.
Copyright (c) 2002, 2003, 2004, 2005, 2006, 2007, 2008 Jarkko
Hietaniemi. All rights reserved.
Copyright (C) 2011, 2012, 2013 Andrew Main (Zefram) <zefram@fysh.org>
This program is free software; you can redistribute it and/or modify it
under the same terms as Perl itself.
perl v5.40.1 2026-08-30 Time::HiRes(3perl)
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