1HiRes(3)              User Contributed Perl Documentation             HiRes(3)
2
3
4

NAME

6       Time::HiRes - High resolution alarm, sleep, gettimeofday, interval
7       timers
8

SYNOPSIS

10         use Time::HiRes qw( usleep ualarm gettimeofday tv_interval nanosleep
11                             clock_gettime clock_getres clock_nanosleep clock
12                             stat lstat utime);
13
14         usleep ($microseconds);
15         nanosleep ($nanoseconds);
16
17         ualarm ($microseconds);
18         ualarm ($microseconds, $interval_microseconds);
19
20         $t0 = [gettimeofday];
21         ($seconds, $microseconds) = gettimeofday;
22
23         $elapsed = tv_interval ( $t0, [$seconds, $microseconds]);
24         $elapsed = tv_interval ( $t0, [gettimeofday]);
25         $elapsed = tv_interval ( $t0 );
26
27         use Time::HiRes qw ( time alarm sleep );
28
29         $now_fractions = time;
30         sleep ($floating_seconds);
31         alarm ($floating_seconds);
32         alarm ($floating_seconds, $floating_interval);
33
34         use Time::HiRes qw( setitimer getitimer );
35
36         setitimer ($which, $floating_seconds, $floating_interval );
37         getitimer ($which);
38
39         use Time::HiRes qw( clock_gettime clock_getres clock_nanosleep
40                             ITIMER_REAL ITIMER_VIRTUAL ITIMER_PROF
41                             ITIMER_REALPROF );
42
43         $realtime   = clock_gettime(CLOCK_REALTIME);
44         $resolution = clock_getres(CLOCK_REALTIME);
45
46         clock_nanosleep(CLOCK_REALTIME, 1.5e9);
47         clock_nanosleep(CLOCK_REALTIME, time()*1e9 + 10e9, TIMER_ABSTIME);
48
49         my $ticktock = clock();
50
51         use Time::HiRes qw( stat lstat );
52
53         my @stat = stat("file");
54         my @stat = stat(FH);
55         my @stat = lstat("file");
56
57         use Time::HiRes qw( utime );
58         utime $floating_seconds, $floating_seconds, file...;
59

DESCRIPTION

61       The "Time::HiRes" module implements a Perl interface to the "usleep",
62       "nanosleep", "ualarm", "gettimeofday", and "setitimer"/"getitimer"
63       system calls, in other words, high resolution time and timers. See the
64       "EXAMPLES" section below and the test scripts for usage; see your
65       system documentation for the description of the underlying "nanosleep"
66       or "usleep", "ualarm", "gettimeofday", and "setitimer"/"getitimer"
67       calls.
68
69       If your system lacks "gettimeofday()" or an emulation of it you don't
70       get "gettimeofday()" or the one-argument form of "tv_interval()".  If
71       your system lacks all of "nanosleep()", "usleep()", "select()", and
72       "poll", you don't get "Time::HiRes::usleep()",
73       "Time::HiRes::nanosleep()", or "Time::HiRes::sleep()".  If your system
74       lacks both "ualarm()" and "setitimer()" you don't get
75       "Time::HiRes::ualarm()" or "Time::HiRes::alarm()".
76
77       If you try to import an unimplemented function in the "use" statement
78       it will fail at compile time.
79
80       If your subsecond sleeping is implemented with "nanosleep()" instead of
81       "usleep()", you can mix subsecond sleeping with signals since
82       "nanosleep()" does not use signals.  This, however, is not portable,
83       and you should first check for the truth value of
84       &Time::HiRes::d_nanosleep to see whether you have nanosleep, and then
85       carefully read your "nanosleep()" C API documentation for any
86       peculiarities.
87
88       If you are using "nanosleep" for something else than mixing sleeping
89       with signals, give some thought to whether Perl is the tool you should
90       be using for work requiring nanosecond accuracies.
91
92       Remember that unless you are working on a hard realtime system, any
93       clocks and timers will be imprecise, especially so if you are working
94       in a pre-emptive multiuser system.  Understand the difference between
95       wallclock time and process time (in UNIX-like systems the sum of user
96       and system times).  Any attempt to sleep for X seconds will most
97       probably end up sleeping more than that, but don't be surprised if you
98       end up sleeping slightly less.
99
100       The following functions can be imported from this module.  No functions
101       are exported by default.
102
103       gettimeofday ()
104           In array context returns a two-element array with the seconds and
105           microseconds since the epoch.  In scalar context returns floating
106           seconds like "Time::HiRes::time()" (see below).
107
108       usleep ( $useconds )
109           Sleeps for the number of microseconds (millionths of a second)
110           specified.  Returns the number of microseconds actually slept.  Can
111           sleep for more than one second, unlike the "usleep" system call.
112           Can also sleep for zero seconds, which often works like a thread
113           yield.  See also "Time::HiRes::sleep()", and "clock_nanosleep()".
114
115           Do not expect usleep() to be exact down to one microsecond.
116
117       nanosleep ( $nanoseconds )
118           Sleeps for the number of nanoseconds (1e9ths of a second)
119           specified.  Returns the number of nanoseconds actually slept
120           (accurate only to microseconds, the nearest thousand of them).  Can
121           sleep for more than one second.  Can also sleep for zero seconds,
122           which often works like a thread yield.  See also
123           "Time::HiRes::sleep()", "Time::HiRes::usleep()", and
124           "clock_nanosleep()".
125
126           Do not expect nanosleep() to be exact down to one nanosecond.
127           Getting even accuracy of one thousand nanoseconds is good.
128
129       ualarm ( $useconds [, $interval_useconds ] )
130           Issues a "ualarm" call; the $interval_useconds is optional and will
131           be zero if unspecified, resulting in "alarm"-like behaviour.
132
133           Returns the remaining time in the alarm in microseconds, or "undef"
134           if an error occurred.
135
136           ualarm(0) will cancel an outstanding ualarm().
137
138           Note that the interaction between alarms and sleeps is unspecified.
139
140       tv_interval
141           tv_interval ( $ref_to_gettimeofday [, $ref_to_later_gettimeofday] )
142
143           Returns the floating seconds between the two times, which should
144           have been returned by "gettimeofday()". If the second argument is
145           omitted, then the current time is used.
146
147       time ()
148           Returns a floating seconds since the epoch. This function can be
149           imported, resulting in a nice drop-in replacement for the "time"
150           provided with core Perl; see the "EXAMPLES" below.
151
152           NOTE 1: This higher resolution timer can return values either less
153           or more than the core "time()", depending on whether your platform
154           rounds the higher resolution timer values up, down, or to the
155           nearest second to get the core "time()", but naturally the
156           difference should be never more than half a second.  See also
157           "clock_getres", if available in your system.
158
159           NOTE 2: Since Sunday, September 9th, 2001 at 01:46:40 AM GMT, when
160           the "time()" seconds since epoch rolled over to 1_000_000_000, the
161           default floating point format of Perl and the seconds since epoch
162           have conspired to produce an apparent bug: if you print the value
163           of "Time::HiRes::time()" you seem to be getting only five decimals,
164           not six as promised (microseconds).  Not to worry, the microseconds
165           are there (assuming your platform supports such granularity in the
166           first place).  What is going on is that the default floating point
167           format of Perl only outputs 15 digits.  In this case that means ten
168           digits before the decimal separator and five after.  To see the
169           microseconds you can use either "printf"/"sprintf" with "%.6f", or
170           the "gettimeofday()" function in list context, which will give you
171           the seconds and microseconds as two separate values.
172
173       sleep ( $floating_seconds )
174           Sleeps for the specified amount of seconds.  Returns the number of
175           seconds actually slept (a floating point value).  This function can
176           be imported, resulting in a nice drop-in replacement for the
177           "sleep" provided with perl, see the "EXAMPLES" below.
178
179           Note that the interaction between alarms and sleeps is unspecified.
180
181       alarm ( $floating_seconds [, $interval_floating_seconds ] )
182           The "SIGALRM" signal is sent after the specified number of seconds.
183           Implemented using "setitimer()" if available, "ualarm()" if not.
184           The $interval_floating_seconds argument is optional and will be
185           zero if unspecified, resulting in "alarm()"-like behaviour.  This
186           function can be imported, resulting in a nice drop-in replacement
187           for the "alarm" provided with perl, see the "EXAMPLES" below.
188
189           Returns the remaining time in the alarm in seconds, or "undef" if
190           an error occurred.
191
192           NOTE 1: With some combinations of operating systems and Perl
193           releases "SIGALRM" restarts "select()", instead of interrupting it.
194           This means that an "alarm()" followed by a "select()" may together
195           take the sum of the times specified for the "alarm()" and the
196           "select()", not just the time of the "alarm()".
197
198           Note that the interaction between alarms and sleeps is unspecified.
199
200       setitimer ( $which, $floating_seconds [, $interval_floating_seconds ] )
201           Start up an interval timer: after a certain time, a signal ($which)
202           arrives, and more signals may keep arriving at certain intervals.
203           To disable an "itimer", use $floating_seconds of zero.  If the
204           $interval_floating_seconds is set to zero (or unspecified), the
205           timer is disabled after the next delivered signal.
206
207           Use of interval timers may interfere with "alarm()", "sleep()", and
208           "usleep()".  In standard-speak the "interaction is unspecified",
209           which means that anything may happen: it may work, it may not.
210
211           In scalar context, the remaining time in the timer is returned.
212
213           In list context, both the remaining time and the interval are
214           returned.
215
216           There are usually three or four interval timers (signals)
217           available: the $which can be "ITIMER_REAL", "ITIMER_VIRTUAL",
218           "ITIMER_PROF", or "ITIMER_REALPROF".  Note that which ones are
219           available depends: true UNIX platforms usually have the first
220           three, but only Solaris seems to have "ITIMER_REALPROF" (which is
221           used to profile multithreaded programs).  Win32 unfortunately does
222           not have interval timers.
223
224           "ITIMER_REAL" results in "alarm()"-like behaviour.  Time is counted
225           in real time; that is, wallclock time.  "SIGALRM" is delivered when
226           the timer expires.
227
228           "ITIMER_VIRTUAL" counts time in (process) virtual time; that is,
229           only when the process is running.  In multiprocessor/user/CPU
230           systems this may be more or less than real or wallclock time.
231           (This time is also known as the user time.)  "SIGVTALRM" is
232           delivered when the timer expires.
233
234           "ITIMER_PROF" counts time when either the process virtual time or
235           when the operating system is running on behalf of the process (such
236           as I/O).  (This time is also known as the system time.)  (The sum
237           of user time and system time is known as the CPU time.)  "SIGPROF"
238           is delivered when the timer expires.  "SIGPROF" can interrupt
239           system calls.
240
241           The semantics of interval timers for multithreaded programs are
242           system-specific, and some systems may support additional interval
243           timers.  For example, it is unspecified which thread gets the
244           signals.  See your setitimer(2) documentation.
245
246       getitimer ( $which )
247           Return the remaining time in the interval timer specified by
248           $which.
249
250           In scalar context, the remaining time is returned.
251
252           In list context, both the remaining time and the interval are
253           returned.  The interval is always what you put in using
254           "setitimer()".
255
256       clock_gettime ( $which )
257           Return as seconds the current value of the POSIX high resolution
258           timer specified by $which.  All implementations that support POSIX
259           high resolution timers are supposed to support at least the $which
260           value of "CLOCK_REALTIME", which is supposed to return results
261           close to the results of "gettimeofday", or the number of seconds
262           since 00:00:00:00 January 1, 1970 Greenwich Mean Time (GMT).  Do
263           not assume that CLOCK_REALTIME is zero, it might be one, or
264           something else.  Another potentially useful (but not available
265           everywhere) value is "CLOCK_MONOTONIC", which guarantees a
266           monotonically increasing time value (unlike time() or
267           gettimeofday(), which can be adjusted).  See your system
268           documentation for other possibly supported values.
269
270       clock_getres ( $which )
271           Return as seconds the resolution of the POSIX high resolution timer
272           specified by $which.  All implementations that support POSIX high
273           resolution timers are supposed to support at least the $which value
274           of "CLOCK_REALTIME", see "clock_gettime".
275
276           NOTE: the resolution returned may be highly optimistic.  Even if
277           the resolution is high (a small number), all it means is that
278           you'll be able to specify the arguments to clock_gettime() and
279           clock_nanosleep() with that resolution.  The system might not
280           actually be able to measure events at that resolution, and the
281           various overheads and the overall system load are certain to affect
282           any timings.
283
284       clock_nanosleep ( $which, $nanoseconds, $flags = 0)
285           Sleeps for the number of nanoseconds (1e9ths of a second)
286           specified.  Returns the number of nanoseconds actually slept.  The
287           $which is the "clock id", as with clock_gettime() and
288           clock_getres().  The flags default to zero but "TIMER_ABSTIME" can
289           specified (must be exported explicitly) which means that
290           $nanoseconds is not a time interval (as is the default) but instead
291           an absolute time.  Can sleep for more than one second.  Can also
292           sleep for zero seconds, which often works like a thread yield.  See
293           also "Time::HiRes::sleep()", "Time::HiRes::usleep()", and
294           "Time::HiRes::nanosleep()".
295
296           Do not expect clock_nanosleep() to be exact down to one nanosecond.
297           Getting even accuracy of one thousand nanoseconds is good.
298
299       clock()
300           Return as seconds the process time (user + system time) spent by
301           the process since the first call to clock() (the definition is not
302           "since the start of the process", though if you are lucky these
303           times may be quite close to each other, depending on the system).
304           What this means is that you probably need to store the result of
305           your first call to clock(), and subtract that value from the
306           following results of clock().
307
308           The time returned also includes the process times of the terminated
309           child processes for which wait() has been executed.  This value is
310           somewhat like the second value returned by the times() of core
311           Perl, but not necessarily identical.  Note that due to backward
312           compatibility limitations the returned value may wrap around at
313           about 2147 seconds or at about 36 minutes.
314
315       stat
316       stat FH
317       stat EXPR
318       lstat
319       lstat FH
320       lstat EXPR
321           As "stat" in perlfunc or "lstat" in perlfunc but with the
322           access/modify/change file timestamps in subsecond resolution, if
323           the operating system and the filesystem both support such
324           timestamps.  To override the standard stat():
325
326               use Time::HiRes qw(stat);
327
328           Test for the value of &Time::HiRes::d_hires_stat to find out
329           whether the operating system supports subsecond file timestamps: a
330           value larger than zero means yes. There are unfortunately no easy
331           ways to find out whether the filesystem supports such timestamps.
332           UNIX filesystems often do; NTFS does; FAT doesn't (FAT timestamp
333           granularity is two seconds).
334
335           A zero return value of &Time::HiRes::d_hires_stat means that
336           Time::HiRes::stat is a no-op passthrough for CORE::stat() (and
337           likewise for lstat), and therefore the timestamps will stay
338           integers.  The same thing will happen if the filesystem does not do
339           subsecond timestamps, even if the &Time::HiRes::d_hires_stat is
340           non-zero.
341
342           In any case do not expect nanosecond resolution, or even a
343           microsecond resolution.  Also note that the modify/access
344           timestamps might have different resolutions, and that they need not
345           be synchronized, e.g.  if the operations are
346
347               write
348               stat # t1
349               read
350               stat # t2
351
352           the access time stamp from t2 need not be greater-than the modify
353           time stamp from t1: it may be equal or less.
354
355       utime LIST
356           As "utime" in perlfunc but with the ability to set the
357           access/modify file timestamps in subsecond resolution, if the
358           operating system and the filesystem, and the mount options of the
359           filesystem, all support such timestamps.
360
361           To override the standard utime():
362
363               use Time::HiRes qw(utime);
364
365           Test for the value of &Time::HiRes::d_hires_utime to find out
366           whether the operating system supports setting subsecond file
367           timestamps.
368
369           As with CORE::utime(), passing undef as both the atime and mtime
370           will call the syscall with a NULL argument.
371
372           The actual achievable subsecond resolution depends on the
373           combination of the operating system and the filesystem.
374
375           Modifying the timestamps may not be possible at all: for example,
376           the "noatime" filesystem mount option may prohibit you from
377           changing the access time timestamp.
378
379           Returns the number of files successfully changed.
380

EXAMPLES

382         use Time::HiRes qw(usleep ualarm gettimeofday tv_interval);
383
384         $microseconds = 750_000;
385         usleep($microseconds);
386
387         # signal alarm in 2.5s & every .1s thereafter
388         ualarm(2_500_000, 100_000);
389         # cancel that ualarm
390         ualarm(0);
391
392         # get seconds and microseconds since the epoch
393         ($s, $usec) = gettimeofday();
394
395         # measure elapsed time
396         # (could also do by subtracting 2 gettimeofday return values)
397         $t0 = [gettimeofday];
398         # do bunch of stuff here
399         $t1 = [gettimeofday];
400         # do more stuff here
401         $t0_t1 = tv_interval $t0, $t1;
402
403         $elapsed = tv_interval ($t0, [gettimeofday]);
404         $elapsed = tv_interval ($t0); # equivalent code
405
406         #
407         # replacements for time, alarm and sleep that know about
408         # floating seconds
409         #
410         use Time::HiRes;
411         $now_fractions = Time::HiRes::time;
412         Time::HiRes::sleep (2.5);
413         Time::HiRes::alarm (10.6666666);
414
415         use Time::HiRes qw ( time alarm sleep );
416         $now_fractions = time;
417         sleep (2.5);
418         alarm (10.6666666);
419
420         # Arm an interval timer to go off first at 10 seconds and
421         # after that every 2.5 seconds, in process virtual time
422
423         use Time::HiRes qw ( setitimer ITIMER_VIRTUAL time );
424
425         $SIG{VTALRM} = sub { print time, "\n" };
426         setitimer(ITIMER_VIRTUAL, 10, 2.5);
427
428         use Time::HiRes qw( clock_gettime clock_getres CLOCK_REALTIME );
429         # Read the POSIX high resolution timer.
430         my $high = clock_gettime(CLOCK_REALTIME);
431         # But how accurate we can be, really?
432         my $reso = clock_getres(CLOCK_REALTIME);
433
434         use Time::HiRes qw( clock_nanosleep TIMER_ABSTIME );
435         clock_nanosleep(CLOCK_REALTIME, 1e6);
436         clock_nanosleep(CLOCK_REALTIME, 2e9, TIMER_ABSTIME);
437
438         use Time::HiRes qw( clock );
439         my $clock0 = clock();
440         ... # Do something.
441         my $clock1 = clock();
442         my $clockd = $clock1 - $clock0;
443
444         use Time::HiRes qw( stat );
445         my ($atime, $mtime, $ctime) = (stat("istics"))[8, 9, 10];
446

C API

448       In addition to the perl API described above, a C API is available for
449       extension writers.  The following C functions are available in the
450       modglobal hash:
451
452         name             C prototype
453         ---------------  ----------------------
454         Time::NVtime     NV (*)()
455         Time::U2time     void (*)(pTHX_ UV ret[2])
456
457       Both functions return equivalent information (like "gettimeofday") but
458       with different representations.  The names "NVtime" and "U2time" were
459       selected mainly because they are operating system independent.
460       ("gettimeofday" is Unix-centric, though some platforms like Win32 and
461       VMS have emulations for it.)
462
463       Here is an example of using "NVtime" from C:
464
465         NV (*myNVtime)(); /* Returns -1 on failure. */
466         SV **svp = hv_fetchs(PL_modglobal, "Time::NVtime", 0);
467         if (!svp)         croak("Time::HiRes is required");
468         if (!SvIOK(*svp)) croak("Time::NVtime isn't a function pointer");
469         myNVtime = INT2PTR(NV(*)(), SvIV(*svp));
470         printf("The current time is: %" NVff "\n", (*myNVtime)());
471

DIAGNOSTICS

473   useconds or interval more than ...
474       In ualarm() you tried to use number of microseconds or interval (also
475       in microseconds) more than 1_000_000 and setitimer() is not available
476       in your system to emulate that case.
477
478   negative time not invented yet
479       You tried to use a negative time argument.
480
481   internal error: useconds < 0 (unsigned ... signed ...)
482       Something went horribly wrong-- the number of microseconds that cannot
483       become negative just became negative.  Maybe your compiler is broken?
484
485   useconds or uinterval equal to or more than 1000000
486       In some platforms it is not possible to get an alarm with subsecond
487       resolution and later than one second.
488
489   unimplemented in this platform
490       Some calls simply aren't available, real or emulated, on every
491       platform.
492

CAVEATS

494       Notice that the core "time()" maybe rounding rather than truncating.
495       What this means is that the core "time()" may be reporting the time as
496       one second later than "gettimeofday()" and "Time::HiRes::time()".
497
498       Adjusting the system clock (either manually or by services like ntp)
499       may cause problems, especially for long running programs that assume a
500       monotonously increasing time (note that all platforms do not adjust
501       time as gracefully as UNIX ntp does).  For example in Win32 (and
502       derived platforms like Cygwin and MinGW) the Time::HiRes::time() may
503       temporarily drift off from the system clock (and the original time())
504       by up to 0.5 seconds. Time::HiRes will notice this eventually and
505       recalibrate.  Note that since Time::HiRes 1.77 the
506       clock_gettime(CLOCK_MONOTONIC) might help in this (in case your system
507       supports CLOCK_MONOTONIC).
508
509       Some systems have APIs but not implementations: for example QNX and
510       Haiku have the interval timer APIs but not the functionality.
511
512       In pre-Sierra macOS (pre-10.12, OS X) clock_getres(), clock_gettime()
513       and clock_nanosleep() are emulated using the Mach timers; as a side
514       effect of being emulated the CLOCK_REALTIME and CLOCK_MONOTONIC are the
515       same timer.
516
517       gnukfreebsd seems to have non-functional futimens() and utimensat() (at
518       least as of 10.1): therefore the hires utime() does not work.
519

SEE ALSO

521       Perl modules BSD::Resource, Time::TAI64.
522
523       Your system documentation for clock(3), clock_gettime(2),
524       clock_getres(3), clock_nanosleep(3), clock_settime(2), getitimer(2),
525       gettimeofday(2), setitimer(2), sleep(3), stat(2), ualarm(3).
526

AUTHORS

528       D. Wegscheid <wegscd@whirlpool.com> R. Schertler <roderick@argon.org>
529       J. Hietaniemi <jhi@iki.fi> G. Aas <gisle@aas.no>
530
532       Copyright (c) 1996-2002 Douglas E. Wegscheid.  All rights reserved.
533
534       Copyright (c) 2002, 2003, 2004, 2005, 2006, 2007, 2008 Jarkko
535       Hietaniemi.  All rights reserved.
536
537       Copyright (C) 2011, 2012, 2013 Andrew Main (Zefram) <zefram@fysh.org>
538
539       This program is free software; you can redistribute it and/or modify it
540       under the same terms as Perl itself.
541
542
543
544perl v5.36.0                      2022-07-22                          HiRes(3)
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