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", "get-timeofday", "gettimeofday",
timeofday", 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 documenta-tion documentation
tion 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 sub-second subsecond
second sleeping with signals since "nanosleep()" does not use signals. This, however, is not porta-ble, portable,
ble, 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.
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 thou-sand thousand
sand 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 "gettime-ofday()". "gettimeofday()".
ofday()". 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 (microsec-onds). (microseconds).
onds). Not to worry, the microseconds are there (assuming your platform supports such granular-ity granularity
ity 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 "get-timeofday()" "gettimeofday()"
timeofday()" 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
"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 dropin
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 standardspeak
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 pro-file profile
file multithreaded programs).
"ITIMER_REAL" results in "alarm()"-like behaviour. Time is counted in real time; that is, wall-clock wallclock
clock time. "SIGALRM" is delivered when the timer expires.
"ITIMER_VIRTUAL" counts time in (process) virtual time; that is, only when the process is run-ning. running.
ning. 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. 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 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(), which can be adjusted). See your system doc-umentation documentation
umentation 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".
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
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.
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 follow-ing following
ing C functions are available in the modglobal hash:
name C prototype
--------------- ----------------------Time::NVtime ---------------------Time::NVtime
Time::NVtime double (*)()
Time::U2time void (*)(pTHX_ UV ret[2])
Both functions return equivalent information (like "gettimeofday") but with different representa-tions. representations.
tions. The names "NVtime" and "U2time" were selected mainly because they are operating system inde-pendent. independent.
pendent. ("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 negative 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 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).
SEE ALSO
Perl modules BSD::Resource, Time::TAI64.
Your system documentation for "clock_gettime", "clock_settime", "gettimeofday", "getitimer",
"setitimer", "ualarm".
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 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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