1HiRes(3) User Contributed Perl Documentation HiRes(3)
2
6 Time::HiRes - High resolution alarm, sleep, gettimeofday, interval
7 timers
8
10 use Time::HiRes qw( usleep ualarm gettimeofday tv_interval nanosleep
11 clock_gettime clock_getres clock_nanosleep clock
12 stat lstat utime);
13 usleep ($microseconds);
15 nanosleep ($nanoseconds);
16 ualarm ($microseconds);
18 ualarm ($microseconds, $interval_microseconds);
19 $t0 = [gettimeofday];
21 ($seconds, $microseconds) = gettimeofday;
22 $elapsed = tv_interval ( $t0, [$seconds, $microseconds]);
24 $elapsed = tv_interval ( $t0, [gettimeofday]);
25 $elapsed = tv_interval ( $t0 );
26 use Time::HiRes qw ( time alarm sleep );
28 $now_fractions = time;
30 sleep ($floating_seconds);
31 alarm ($floating_seconds);
32 alarm ($floating_seconds, $floating_interval);
33 use Time::HiRes qw( setitimer getitimer );
35 setitimer ($which, $floating_seconds, $floating_interval );
37 getitimer ($which);
38 use Time::HiRes qw( clock_gettime clock_getres clock_nanosleep
40 ITIMER_REAL ITIMER_VIRTUAL ITIMER_PROF
41 ITIMER_REALPROF );
42 $realtime = clock_gettime(CLOCK_REALTIME);
44 $resolution = clock_getres(CLOCK_REALTIME);
45 clock_nanosleep(CLOCK_REALTIME, 1.5e9);
47 clock_nanosleep(CLOCK_REALTIME, time()*1e9 + 10e9, TIMER_ABSTIME);
48 my $ticktock = clock();
50 use Time::HiRes qw( stat lstat );
52 my @stat = stat("file");
54 my @stat = stat(FH);
55 my @stat = lstat("file");
56 use Time::HiRes qw( utime );
58 utime $floating_seconds, $floating_seconds, file...;
59
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 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 If you try to import an unimplemented function in the "use" statement
78 it will fail at compile time.
79 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 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 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 The following functions can be imported from this module. No functions
101 are exported by default.
102 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 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::usleep()", "Time::HiRes::sleep()",
114 and "Time::HiRes::clock_nanosleep()".
115 Do not expect usleep() to be exact down to one microsecond.
117 nanosleep ( $nanoseconds )
119 Sleeps for the number of nanoseconds (1e9ths of a second)
120 specified. Returns the number of nanoseconds actually slept
121 (accurate only to microseconds, the nearest thousand of them). Can
122 sleep for more than one second. Can also sleep for zero seconds,
123 which often works like a thread yield. See also
124 "Time::HiRes::sleep()", "Time::HiRes::usleep()", and
125 "Time::HiRes::clock_nanosleep()".
126 Do not expect nanosleep() to be exact down to one nanosecond.
128 Getting even accuracy of one thousand nanoseconds is good.
129 ualarm ( $useconds [, $interval_useconds ] )
131 Issues a "ualarm" call; the $interval_useconds is optional and will
132 be zero if unspecified, resulting in "alarm"-like behaviour.
133 Returns the remaining time in the alarm in microseconds, or "undef"
135 if an error occurred.
136 ualarm(0) will cancel an outstanding ualarm().
138 Note that the interaction between alarms and sleeps is unspecified.
140 tv_interval
142 tv_interval ( $ref_to_gettimeofday [, $ref_to_later_gettimeofday] )
143 Returns the floating seconds between the two times, which should
145 have been returned by "gettimeofday()". If the second argument is
146 omitted, then the current time is used.
147 time ()
149 Returns a floating seconds since the epoch. This function can be
150 imported, resulting in a nice drop-in replacement for the "time"
151 provided with core Perl; see the "EXAMPLES" below.
152 NOTE 1: This higher resolution timer can return values either less
154 or more than the core "time()", depending on whether your platform
155 rounds the higher resolution timer values up, down, or to the
156 nearest second to get the core "time()", but naturally the
157 difference should be never more than half a second. See also
158 "clock_getres", if available in your system.
159 NOTE 2: Since Sunday, September 9th, 2001 at 01:46:40 AM GMT, when
161 the "time()" seconds since epoch rolled over to 1_000_000_000, the
162 default floating point format of Perl and the seconds since epoch
163 have conspired to produce an apparent bug: if you print the value
164 of "Time::HiRes::time()" you seem to be getting only five decimals,
165 not six as promised (microseconds). Not to worry, the microseconds
166 are there (assuming your platform supports such granularity in the
167 first place). What is going on is that the default floating point
168 format of Perl only outputs 15 digits. In this case that means ten
169 digits before the decimal separator and five after. To see the
170 microseconds you can use either "printf"/"sprintf" with "%.6f", or
171 the "gettimeofday()" function in list context, which will give you
172 the seconds and microseconds as two separate values.
173 sleep ( $floating_seconds )
175 Sleeps for the specified amount of seconds. Returns the number of
176 seconds actually slept (a floating point value). This function can
177 be imported, resulting in a nice drop-in replacement for the
178 "sleep" provided with perl, see the "EXAMPLES" below.
179 Note that the interaction between alarms and sleeps is unspecified.
181 alarm ( $floating_seconds [, $interval_floating_seconds ] )
183 The "SIGALRM" signal is sent after the specified number of seconds.
184 Implemented using "setitimer()" if available, "ualarm()" if not.
185 The $interval_floating_seconds argument is optional and will be
186 zero if unspecified, resulting in "alarm()"-like behaviour. This
187 function can be imported, resulting in a nice drop-in replacement
188 for the "alarm" provided with perl, see the "EXAMPLES" below.
189 Returns the remaining time in the alarm in seconds, or "undef" if
191 an error occurred.
192 NOTE 1: With some combinations of operating systems and Perl
194 releases "SIGALRM" restarts "select()", instead of interrupting it.
195 This means that an "alarm()" followed by a "select()" may together
196 take the sum of the times specified for the "alarm()" and the
197 "select()", not just the time of the "alarm()".
198 Note that the interaction between alarms and sleeps is unspecified.
200 setitimer ( $which, $floating_seconds [, $interval_floating_seconds ] )
202 Start up an interval timer: after a certain time, a signal ($which)
203 arrives, and more signals may keep arriving at certain intervals.
204 To disable an "itimer", use $floating_seconds of zero. If the
205 $interval_floating_seconds is set to zero (or unspecified), the
206 timer is disabled after the next delivered signal.
207 Use of interval timers may interfere with "alarm()", "sleep()", and
209 "usleep()". In standard-speak the "interaction is unspecified",
210 which means that anything may happen: it may work, it may not.
211 In scalar context, the remaining time in the timer is returned.
213 In list context, both the remaining time and the interval are
215 returned.
216 There are usually three or four interval timers (signals)
218 available: the $which can be "ITIMER_REAL", "ITIMER_VIRTUAL",
219 "ITIMER_PROF", or "ITIMER_REALPROF". Note that which ones are
220 available depends: true UNIX platforms usually have the first
221 three, but only Solaris seems to have "ITIMER_REALPROF" (which is
222 used to profile multithreaded programs). Win32 unfortunately does
223 not have interval timers.
224 "ITIMER_REAL" results in "alarm()"-like behaviour. Time is counted
226 in real time; that is, wallclock time. "SIGALRM" is delivered when
227 the timer expires.
228 "ITIMER_VIRTUAL" counts time in (process) virtual time; that is,
230 only when the process is running. In multiprocessor/user/CPU
231 systems this may be more or less than real or wallclock time.
232 (This time is also known as the user time.) "SIGVTALRM" is
233 delivered when the timer expires.
234 "ITIMER_PROF" counts time when either the process virtual time or
236 when the operating system is running on behalf of the process (such
237 as I/O). (This time is also known as the system time.) (The sum
238 of user time and system time is known as the CPU time.) "SIGPROF"
239 is delivered when the timer expires. "SIGPROF" can interrupt
240 system calls.
241 The semantics of interval timers for multithreaded programs are
243 system-specific, and some systems may support additional interval
244 timers. For example, it is unspecified which thread gets the
245 signals. See your "setitimer()" documentation.
246 getitimer ( $which )
248 Return the remaining time in the interval timer specified by
249 $which.
250 In scalar context, the remaining time is returned.
252 In list context, both the remaining time and the interval are
254 returned. The interval is always what you put in using
255 "setitimer()".
256 clock_gettime ( $which )
258 Return as seconds the current value of the POSIX high resolution
259 timer specified by $which. All implementations that support POSIX
260 high resolution timers are supposed to support at least the $which
261 value of "CLOCK_REALTIME", which is supposed to return results
262 close to the results of "gettimeofday", or the number of seconds
263 since 00:00:00:00 January 1, 1970 Greenwich Mean Time (GMT). Do
264 not assume that CLOCK_REALTIME is zero, it might be one, or
265 something else. Another potentially useful (but not available
266 everywhere) value is "CLOCK_MONOTONIC", which guarantees a
267 monotonically increasing time value (unlike time() or
268 gettimeofday(), which can be adjusted). See your system
269 documentation for other possibly supported values.
270 clock_getres ( $which )
272 Return as seconds the resolution of the POSIX high resolution timer
273 specified by $which. All implementations that support POSIX high
274 resolution timers are supposed to support at least the $which value
275 of "CLOCK_REALTIME", see "clock_gettime".
276 NOTE: the resolution returned may be highly optimistic. Even if
278 the resolution is high (a small number), all it means is that
279 you'll be able to specify the arguments to clock_gettime() and
280 clock_nanosleep() with that resolution. The system might not
281 actually be able to measure events at that resolution, and the
282 various overheads and the overall system load are certain to affect
283 any timings.
284 clock_nanosleep ( $which, $nanoseconds, $flags = 0)
286 Sleeps for the number of nanoseconds (1e9ths of a second)
287 specified. Returns the number of nanoseconds actually slept. The
288 $which is the "clock id", as with clock_gettime() and
289 clock_getres(). The flags default to zero but "TIMER_ABSTIME" can
290 specified (must be exported explicitly) which means that
291 $nanoseconds is not a time interval (as is the default) but instead
292 an absolute time. Can sleep for more than one second. Can also
293 sleep for zero seconds, which often works like a thread yield. See
294 also "Time::HiRes::sleep()", "Time::HiRes::usleep()", and
295 "Time::HiRes::nanosleep()".
296 Do not expect clock_nanosleep() to be exact down to one nanosecond.
298 Getting even accuracy of one thousand nanoseconds is good.
299 clock()
301 Return as seconds the process time (user + system time) spent by
302 the process since the first call to clock() (the definition is not
303 "since the start of the process", though if you are lucky these
304 times may be quite close to each other, depending on the system).
305 What this means is that you probably need to store the result of
306 your first call to clock(), and subtract that value from the
307 following results of clock().
308 The time returned also includes the process times of the terminated
310 child processes for which wait() has been executed. This value is
311 somewhat like the second value returned by the times() of core
312 Perl, but not necessarily identical. Note that due to backward
313 compatibility limitations the returned value may wrap around at
314 about 2147 seconds or at about 36 minutes.
315 stat
317 stat FH
318 stat EXPR
319 lstat
320 lstat FH
321 lstat EXPR
322 As "stat" in perlfunc or "lstat" in perlfunc but with the
323 access/modify/change file timestamps in subsecond resolution, if
324 the operating system and the filesystem both support such
325 timestamps. To override the standard stat():
326 use Time::HiRes qw(stat);
328 Test for the value of &Time::HiRes::d_hires_stat to find out
330 whether the operating system supports subsecond file timestamps: a
331 value larger than zero means yes. There are unfortunately no easy
332 ways to find out whether the filesystem supports such timestamps.
333 UNIX filesystems often do; NTFS does; FAT doesn't (FAT timestamp
334 granularity is two seconds).
335 A zero return value of &Time::HiRes::d_hires_stat means that
337 Time::HiRes::stat is a no-op passthrough for CORE::stat() (and
338 likewise for lstat), and therefore the timestamps will stay
339 integers. The same thing will happen if the filesystem does not do
340 subsecond timestamps, even if the &Time::HiRes::d_hires_stat is
341 non-zero.
342 In any case do not expect nanosecond resolution, or even a
344 microsecond resolution. Also note that the modify/access
345 timestamps might have different resolutions, and that they need not
346 be synchronized, e.g. if the operations are
347 write
349 stat # t1
350 read
351 stat # t2
352 the access time stamp from t2 need not be greater-than the modify
354 time stamp from t1: it may be equal or less.
355 utime LIST
357 As "utime" in perlfunc but with the ability to set the
358 access/modify file timestamps in subsecond resolution, if the
359 operating system and the filesystem, and the mount options of the
360 filesystem, all support such timestamps.
361 To override the standard utime():
363 use Time::HiRes qw(utime);
365 Test for the value of &Time::HiRes::d_hires_utime to find out
367 whether the operating system supports setting subsecond file
368 timestamps.
369 As with CORE::utime(), passing undef as both the atime and mtime
371 will call the syscall with a NULL argument.
372 The actual achievable subsecond resolution depends on the
374 combination of the operating system and the filesystem.
375 Modifying the timestamps may not be possible at all: for example,
377 the "noatime" filesystem mount option may prohibit you from
378 changing the access time timestamp.
379 Returns the number of files successfully changed.
381
383 use Time::HiRes qw(usleep ualarm gettimeofday tv_interval);
384 $microseconds = 750_000;
386 usleep($microseconds);
387 # signal alarm in 2.5s & every .1s thereafter
389 ualarm(2_500_000, 100_000);
390 # cancel that ualarm
391 ualarm(0);
392 # get seconds and microseconds since the epoch
394 ($s, $usec) = gettimeofday();
395 # measure elapsed time
397 # (could also do by subtracting 2 gettimeofday return values)
398 $t0 = [gettimeofday];
399 # do bunch of stuff here
400 $t1 = [gettimeofday];
401 # do more stuff here
402 $t0_t1 = tv_interval $t0, $t1;
403 $elapsed = tv_interval ($t0, [gettimeofday]);
405 $elapsed = tv_interval ($t0); # equivalent code
406 #
408 # replacements for time, alarm and sleep that know about
409 # floating seconds
410 #
411 use Time::HiRes;
412 $now_fractions = Time::HiRes::time;
413 Time::HiRes::sleep (2.5);
414 Time::HiRes::alarm (10.6666666);
415 use Time::HiRes qw ( time alarm sleep );
417 $now_fractions = time;
418 sleep (2.5);
419 alarm (10.6666666);
420 # Arm an interval timer to go off first at 10 seconds and
422 # after that every 2.5 seconds, in process virtual time
423 use Time::HiRes qw ( setitimer ITIMER_VIRTUAL time );
425 $SIG{VTALRM} = sub { print time, "\n" };
427 setitimer(ITIMER_VIRTUAL, 10, 2.5);
428 use Time::HiRes qw( clock_gettime clock_getres CLOCK_REALTIME );
430 # Read the POSIX high resolution timer.
431 my $high = clock_gettime(CLOCK_REALTIME);
432 # But how accurate we can be, really?
433 my $reso = clock_getres(CLOCK_REALTIME);
434 use Time::HiRes qw( clock_nanosleep TIMER_ABSTIME );
436 clock_nanosleep(CLOCK_REALTIME, 1e6);
437 clock_nanosleep(CLOCK_REALTIME, 2e9, TIMER_ABSTIME);
438 use Time::HiRes qw( clock );
440 my $clock0 = clock();
441 ... # Do something.
442 my $clock1 = clock();
443 my $clockd = $clock1 - $clock0;
444 use Time::HiRes qw( stat );
446 my ($atime, $mtime, $ctime) = (stat("istics"))[8, 9, 10];
447
449 In addition to the perl API described above, a C API is available for
450 extension writers. The following C functions are available in the
451 modglobal hash:
452 name C prototype
454 --------------- ----------------------
455 Time::NVtime NV (*)()
456 Time::U2time void (*)(pTHX_ UV ret[2])
457 Both functions return equivalent information (like "gettimeofday") but
459 with different representations. The names "NVtime" and "U2time" were
460 selected mainly because they are operating system independent.
461 ("gettimeofday" is Unix-centric, though some platforms like Win32 and
462 VMS have emulations for it.)
463 Here is an example of using "NVtime" from C:
465 NV (*myNVtime)(); /* Returns -1 on failure. */
467 SV **svp = hv_fetchs(PL_modglobal, "Time::NVtime", 0);
468 if (!svp) croak("Time::HiRes is required");
469 if (!SvIOK(*svp)) croak("Time::NVtime isn't a function pointer");
470 myNVtime = INT2PTR(NV(*)(), SvIV(*svp));
471 printf("The current time is: %" NVff "\n", (*myNVtime)());
472
474 useconds or interval more than ...
475 In ualarm() you tried to use number of microseconds or interval (also
476 in microseconds) more than 1_000_000 and setitimer() is not available
477 in your system to emulate that case.
478 negative time not invented yet
480 You tried to use a negative time argument.
481 internal error: useconds < 0 (unsigned ... signed ...)
483 Something went horribly wrong-- the number of microseconds that cannot
484 become negative just became negative. Maybe your compiler is broken?
485 useconds or uinterval equal to or more than 1000000
487 In some platforms it is not possible to get an alarm with subsecond
488 resolution and later than one second.
489 unimplemented in this platform
491 Some calls simply aren't available, real or emulated, on every
492 platform.
493
495 Notice that the core "time()" maybe rounding rather than truncating.
496 What this means is that the core "time()" may be reporting the time as
497 one second later than "gettimeofday()" and "Time::HiRes::time()".
498 Adjusting the system clock (either manually or by services like ntp)
500 may cause problems, especially for long running programs that assume a
501 monotonously increasing time (note that all platforms do not adjust
502 time as gracefully as UNIX ntp does). For example in Win32 (and
503 derived platforms like Cygwin and MinGW) the Time::HiRes::time() may
504 temporarily drift off from the system clock (and the original time())
505 by up to 0.5 seconds. Time::HiRes will notice this eventually and
506 recalibrate. Note that since Time::HiRes 1.77 the
507 clock_gettime(CLOCK_MONOTONIC) might help in this (in case your system
508 supports CLOCK_MONOTONIC).
509 Some systems have APIs but not implementations: for example QNX and
511 Haiku have the interval timer APIs but not the functionality.
512 In pre-Sierra macOS (pre-10.12, OS X) clock_getres(), clock_gettime()
514 and clock_nanosleep() are emulated using the Mach timers; as a side
515 effect of being emulated the CLOCK_REALTIME and CLOCK_MONOTONIC are the
516 same timer.
517 gnukfreebsd seems to have non-functional futimens() and utimensat() (at
519 least as of 10.1): therefore the hires utime() does not work.
520
522 Perl modules BSD::Resource, Time::TAI64.
523 Your system documentation for "clock", "clock_gettime", "clock_getres",
525 "clock_nanosleep", "clock_settime", "getitimer", "gettimeofday",
526 "setitimer", "sleep", "stat", "ualarm".
527
529 D. Wegscheid <wegscd@whirlpool.com> R. Schertler <roderick@argon.org>
530 J. Hietaniemi <jhi@iki.fi> G. Aas <gisle@aas.no>
531
533 Copyright (c) 1996-2002 Douglas E. Wegscheid. All rights reserved.
534 Copyright (c) 2002, 2003, 2004, 2005, 2006, 2007, 2008 Jarkko
536 Hietaniemi. All rights reserved.
537 Copyright (C) 2011, 2012, 2013 Andrew Main (Zefram) <zefram@fysh.org>
539 This program is free software; you can redistribute it and/or modify it
541 under the same terms as Perl itself.
542perl v5.30.1 2020-01-30 HiRes(3)