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Time::HiRes(3pm) Perl Programmers Reference Guide Time::HiRes(3pm)
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 );
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, $floating_interval);
use Time::HiRes qw( setitimer getitimer
ITIMER_REAL ITIMER_VIRTUAL ITIMER_PROF ITIMER_REALPROF );
setitimer ($which, $floating_seconds, $floating_interval );
getitimer ($which);
$realtime = clock_gettime(CLOCK_REALTIME);
$resolution = clock_getres(CLOCK_REALTIME);
clock_nanosleep(CLOCK_REALTIME, 1.5);
clock_nanosleep(CLOCK_REALTIME, time() + 10, TIMER_ABSTIME);
my $ticktock = clock();
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 under-
lying "nanosleep" or "usleep", "ualarm", "gettimeofday", and
"setitimer"/"getitimer" calls.
If your system lacks "gettimeofday()" or an emulation of it you don't get "gettime-
ofday()" 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 sig-
nals. 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 requir-
ing nanosecond accuracies.
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::usleep()",
"Time::HiRes::sleep()", and "Time::HiRes::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
"Time::HiRes::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.
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 cur-
rent 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 resolu-
tion 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 appar-
ent 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 con-
text, 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. Imple-
mented using "ualarm()". 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.
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 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 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 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 (for example) Win32 and Cygwin have only "ITIMER_REAL", and
only Solaris seems to have "ITIMER_REALPROF" (which is used to profile multi-
threaded programs).
"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. "SIG-
PROF" can interrupt system calls.
The semantics of interval timers for multithreaded programs are system-spe-
cific, 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()".
clock_gettime ( $which )
Return as seconds the current value of the POSIX high resolution timer speci-
fied 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 num-
ber 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_MONO-
TONIC", which guarantees a monotonically increasing time value (unlike time(),
which can be adjusted). See your system documentation for other possibly sup-
ported 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".
clock_nanosleep ( $which, $seconds, $flags = 0)
Sleeps for the number of seconds (1e9ths of a second) specified. Returns the
number of seconds 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 fol-
lowing results of clock().
The time returned also includes the process times of the terminated child pro-
cesses for which wait() has been executed. This value is somewhat like the
second value returned by the times() of core Perl, but not necessarily identi-
cal. Note that due to backward compatibility limitations the returned value
may wrap around at about 2147 seconds or at about 36 minutes.
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);
# 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_getres(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;
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 double (*)()
Time::U2time void (*)(pTHX_ UV ret[2])
Both functions return equivalent information (like "gettimeofday") but with differ-
ent 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:
double (*myNVtime)(); /* Returns -1 on failure. */
SV **svp = hv_fetch(PL_modglobal, "Time::NVtime", 12, 0);
if (!svp) croak("Time::HiRes is required");
if (!SvIOK(*svp)) croak("Time::NVtime isn't a function pointer");
myNVtime = INT2PTR(double(*)(), SvIV(*svp));
printf("The current time is: %f\n", (*myNVtime)());
DIAGNOSTICS
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 nega-
tive just became negative. Maybe your compiler is broken?
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 increas-
ing 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 origi-
nal 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).
SEE ALSO
Perl modules BSD::Resource, Time::TAI64.
Your system documentation for "clock_gettime", "clock_settime", "gettimeofday",
"getitimer", "setitimer", "ualarm".
AUTHORS
D. Wegscheid <wegscd AT whirlpool.com> R. Schertler <roderick AT argon.org> J. Hietaniemi
<jhi AT iki.fi> G. Aas <gisle AT aas.no>
COPYRIGHT AND LICENSE
Copyright (c) 1996-2002 Douglas E. Wegscheid. All rights reserved.
Copyright (c) 2002, 2003, 2004, 2005 Jarkko Hietaniemi. All rights reserved.
This program is free software; you can redistribute it and/or modify it under the
same terms as Perl itself.
perl v5.8.8 2001-09-21 Time::HiRes(3pm)
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