| Time::HiRes(3perl) | Perl Programmers Reference Guide | Time::HiRes(3perl) |
Time::HiRes - High resolution alarm, sleep, gettimeofday, interval timers
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
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...;
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.
Do not expect usleep() to be exact down to one microsecond.
Do not expect nanosleep() to be exact down to one nanosecond. Getting even accuracy of one thousand nanoseconds is good.
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.
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.
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.
Note that the interaction between alarms and sleeps is unspecified.
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.
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.
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()".
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.
Do not expect clock_nanosleep() to be exact down to one nanosecond. Getting even accuracy of one thousand nanoseconds is good.
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.
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.
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.
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];
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)());
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.
You tried to use a negative time argument.
Something went horribly wrong-- the number of microseconds that cannot become negative just became negative. Maybe your compiler is broken?
In some platforms it is not possible to get an alarm with subsecond resolution and later than one second.
Some calls simply aren't available, real or emulated, on every platform.
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.
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).
D. Wegscheid <wegscd@whirlpool.com> R. Schertler <roderick@argon.org> J. Hietaniemi <jhi@iki.fi> G. Aas <gisle@aas.no>
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.
| 2023-11-25 | perl v5.32.1 |