This is a live mirror of the Perl 5 development currently hosted at https://github.com/perl/perl5
Upgrade to Time-HiRes-1.9703
[perl5.git] / ext / Time / HiRes / HiRes.pm
CommitLineData
dcf686c9
JH
1package Time::HiRes;
2
3use strict;
105cd853 4use vars qw($VERSION $XS_VERSION @ISA @EXPORT @EXPORT_OK $AUTOLOAD);
dcf686c9
JH
5
6require Exporter;
3f2ee006 7require DynaLoader;
dcf686c9 8
0cf8ddea 9@ISA = qw(Exporter DynaLoader);
dcf686c9
JH
10
11@EXPORT = qw( );
3c72ec00 12@EXPORT_OK = qw (usleep sleep ualarm alarm gettimeofday time tv_interval
ced84e60 13 getitimer setitimer nanosleep clock_gettime clock_getres
170c5524 14 clock clock_nanosleep
ced84e60 15 CLOCK_HIGHRES CLOCK_MONOTONIC CLOCK_PROCESS_CPUTIME_ID
170c5524
SP
16 CLOCK_REALTIME CLOCK_SOFTTIME CLOCK_THREAD_CPUTIME_ID
17 CLOCK_TIMEOFDAY CLOCKS_PER_SEC
3f2ee006 18 ITIMER_REAL ITIMER_VIRTUAL ITIMER_PROF ITIMER_REALPROF
170c5524 19 TIMER_ABSTIME
3f2ee006 20 d_usleep d_ualarm d_gettimeofday d_getitimer d_setitimer
170c5524 21 d_nanosleep d_clock_gettime d_clock_getres
75d5269b
SP
22 d_clock d_clock_nanosleep
23 stat
24 );
3f2ee006 25
f3370602 26$VERSION = '1.9703';
105cd853
YST
27$XS_VERSION = $VERSION;
28$VERSION = eval $VERSION;
3c72ec00
JH
29
30sub AUTOLOAD {
31 my $constname;
98b50af3 32 ($constname = $AUTOLOAD) =~ s/.*:://;
ced84e60 33 # print "AUTOLOAD: constname = $constname ($AUTOLOAD)\n";
98b50af3
JH
34 die "&Time::HiRes::constant not defined" if $constname eq 'constant';
35 my ($error, $val) = constant($constname);
ced84e60 36 # print "AUTOLOAD: error = $error, val = $val\n";
0cf8ddea
RGS
37 if ($error) {
38 my (undef,$file,$line) = caller;
39 die "$error at $file line $line.\n";
40 }
3c72ec00
JH
41 {
42 no strict 'refs';
43 *$AUTOLOAD = sub { $val };
44 }
45 goto &$AUTOLOAD;
46}
dcf686c9 47
ced84e60
SP
48sub import {
49 my $this = shift;
50 for my $i (@_) {
170c5524
SP
51 if (($i eq 'clock_getres' && !&d_clock_getres) ||
52 ($i eq 'clock_gettime' && !&d_clock_gettime) ||
53 ($i eq 'clock_nanosleep' && !&d_clock_nanosleep) ||
54 ($i eq 'clock' && !&d_clock) ||
55 ($i eq 'nanosleep' && !&d_nanosleep) ||
56 ($i eq 'usleep' && !&d_usleep) ||
57 ($i eq 'ualarm' && !&d_ualarm)) {
ced84e60
SP
58 require Carp;
59 Carp::croak("Time::HiRes::$i(): unimplemented in this platform");
60 }
61 }
62 Time::HiRes->export_to_level(1, $this, @_);
63}
64
0cf8ddea 65bootstrap Time::HiRes;
dcf686c9
JH
66
67# Preloaded methods go here.
68
69sub tv_interval {
70 # probably could have been done in C
71 my ($a, $b) = @_;
72 $b = [gettimeofday()] unless defined($b);
73 (${$b}[0] - ${$a}[0]) + ((${$b}[1] - ${$a}[1]) / 1_000_000);
74}
75
dcf686c9
JH
76# Autoload methods go after =cut, and are processed by the autosplit program.
77
781;
79__END__
80
81=head1 NAME
82
f7916ddb 83Time::HiRes - High resolution alarm, sleep, gettimeofday, interval timers
dcf686c9
JH
84
85=head1 SYNOPSIS
86
ced84e60 87 use Time::HiRes qw( usleep ualarm gettimeofday tv_interval nanosleep
75d5269b
SP
88 clock_gettime clock_getres clock_nanosleep clock
89 stat );
dcf686c9
JH
90
91 usleep ($microseconds);
44d3ce20 92 nanosleep ($nanoseconds);
dcf686c9
JH
93
94 ualarm ($microseconds);
95 ualarm ($microseconds, $interval_microseconds);
96
97 $t0 = [gettimeofday];
98 ($seconds, $microseconds) = gettimeofday;
99
100 $elapsed = tv_interval ( $t0, [$seconds, $microseconds]);
101 $elapsed = tv_interval ( $t0, [gettimeofday]);
102 $elapsed = tv_interval ( $t0 );
103
104 use Time::HiRes qw ( time alarm sleep );
3c72ec00 105
dcf686c9
JH
106 $now_fractions = time;
107 sleep ($floating_seconds);
108 alarm ($floating_seconds);
109 alarm ($floating_seconds, $floating_interval);
110
3c72ec00 111 use Time::HiRes qw( setitimer getitimer
3f2ee006 112 ITIMER_REAL ITIMER_VIRTUAL ITIMER_PROF ITIMER_REALPROF );
3c72ec00
JH
113
114 setitimer ($which, $floating_seconds, $floating_interval );
115 getitimer ($which);
116
82cbdcc3
SP
117 $realtime = clock_gettime(CLOCK_REALTIME);
118 $resolution = clock_getres(CLOCK_REALTIME);
ced84e60 119
ff7df920
SP
120 clock_nanosleep(CLOCK_REALTIME, 1.5);
121 clock_nanosleep(CLOCK_REALTIME, time() + 10, TIMER_ABSTIME);
170c5524
SP
122
123 my $ticktock = clock();
124
c09e847b 125 my @stat = stat("file");
75d5269b
SP
126 my @stat = stat(FH);
127
dcf686c9
JH
128=head1 DESCRIPTION
129
4ed0e2d4 130The C<Time::HiRes> module implements a Perl interface to the
44d3ce20
RGS
131C<usleep>, C<nanosleep>, C<ualarm>, C<gettimeofday>, and
132C<setitimer>/C<getitimer> system calls, in other words, high
133resolution time and timers. See the L</EXAMPLES> section below and the
134test scripts for usage; see your system documentation for the
135description of the underlying C<nanosleep> or C<usleep>, C<ualarm>,
136C<gettimeofday>, and C<setitimer>/C<getitimer> calls.
dcf686c9 137
6937b144 138If your system lacks C<gettimeofday()> or an emulation of it you don't
4ed0e2d4 139get C<gettimeofday()> or the one-argument form of C<tv_interval()>.
82cbdcc3
SP
140If your system lacks all of C<nanosleep()>, C<usleep()>,
141C<select()>, and C<poll>, you don't get C<Time::HiRes::usleep()>,
142C<Time::HiRes::nanosleep()>, or C<Time::HiRes::sleep()>.
143If your system lacks both C<ualarm()> and C<setitimer()> you don't get
44d3ce20 144C<Time::HiRes::ualarm()> or C<Time::HiRes::alarm()>.
3f2ee006
HS
145
146If you try to import an unimplemented function in the C<use> statement
147it will fail at compile time.
148
4ed0e2d4
RGS
149If your subsecond sleeping is implemented with C<nanosleep()> instead
150of C<usleep()>, you can mix subsecond sleeping with signals since
64a7a97c
RGS
151C<nanosleep()> does not use signals. This, however, is not portable,
152and you should first check for the truth value of
4ed0e2d4
RGS
153C<&Time::HiRes::d_nanosleep> to see whether you have nanosleep, and
154then carefully read your C<nanosleep()> C API documentation for any
44d3ce20 155peculiarities.
0be47ac6 156
0cf8ddea
RGS
157If you are using C<nanosleep> for something else than mixing sleeping
158with signals, give some thought to whether Perl is the tool you should
159be using for work requiring nanosecond accuracies.
dcf686c9 160
3c72ec00
JH
161The following functions can be imported from this module.
162No functions are exported by default.
dcf686c9
JH
163
164=over 4
165
166=item gettimeofday ()
167
0be47ac6 168In array context returns a two-element array with the seconds and
f7916ddb 169microseconds since the epoch. In scalar context returns floating
6937b144 170seconds like C<Time::HiRes::time()> (see below).
dcf686c9
JH
171
172=item usleep ( $useconds )
173
44d3ce20
RGS
174Sleeps for the number of microseconds (millionths of a second)
175specified. Returns the number of microseconds actually slept. Can
170c5524
SP
176sleep for more than one second, unlike the C<usleep> system call. Can
177also sleep for zero seconds, which often works like a I<thread yield>.
178See also C<Time::HiRes::usleep()>, C<Time::HiRes::sleep()>, and
179C<Time::HiRes::clock_nanosleep()>.
44d3ce20
RGS
180
181Do not expect usleep() to be exact down to one microsecond.
182
183=item nanosleep ( $nanoseconds )
184
185Sleeps for the number of nanoseconds (1e9ths of a second) specified.
186Returns the number of nanoseconds actually slept (accurate only to
187microseconds, the nearest thousand of them). Can sleep for more than
170c5524
SP
188one second. Can also sleep for zero seconds, which often works like a
189I<thread yield>. See also C<Time::HiRes::sleep()>,
190C<Time::HiRes::usleep()>, and C<Time::HiRes::clock_nanosleep()>.
44d3ce20
RGS
191
192Do not expect nanosleep() to be exact down to one nanosecond.
193Getting even accuracy of one thousand nanoseconds is good.
dcf686c9
JH
194
195=item ualarm ( $useconds [, $interval_useconds ] )
196
6937b144
MJD
197Issues a C<ualarm> call; the C<$interval_useconds> is optional and
198will be zero if unspecified, resulting in C<alarm>-like behaviour.
dcf686c9 199
993164ab 200Note that the interaction between alarms and sleeps is unspecified.
64a7a97c 201
443572f5
RB
202=item tv_interval
203
0be47ac6 204tv_interval ( $ref_to_gettimeofday [, $ref_to_later_gettimeofday] )
dcf686c9 205
f7916ddb 206Returns the floating seconds between the two times, which should have
6937b144 207been returned by C<gettimeofday()>. If the second argument is omitted,
f7916ddb 208then the current time is used.
dcf686c9
JH
209
210=item time ()
211
f7916ddb 212Returns a floating seconds since the epoch. This function can be
6937b144
MJD
213imported, resulting in a nice drop-in replacement for the C<time>
214provided with core Perl; see the L</EXAMPLES> below.
dcf686c9 215
6937b144
MJD
216B<NOTE 1>: This higher resolution timer can return values either less
217or more than the core C<time()>, depending on whether your platform
218rounds the higher resolution timer values up, down, or to the nearest second
219to get the core C<time()>, but naturally the difference should be never
ced84e60
SP
220more than half a second. See also L</clock_getres>, if available
221in your system.
f7916ddb 222
6937b144
MJD
223B<NOTE 2>: Since Sunday, September 9th, 2001 at 01:46:40 AM GMT, when
224the C<time()> seconds since epoch rolled over to 1_000_000_000, the
0be47ac6
JH
225default floating point format of Perl and the seconds since epoch have
226conspired to produce an apparent bug: if you print the value of
4ed0e2d4
RGS
227C<Time::HiRes::time()> you seem to be getting only five decimals, not
228six as promised (microseconds). Not to worry, the microseconds are
64a7a97c 229there (assuming your platform supports such granularity in the first
4ed0e2d4
RGS
230place). What is going on is that the default floating point format of
231Perl only outputs 15 digits. In this case that means ten digits
232before the decimal separator and five after. To see the microseconds
233you can use either C<printf>/C<sprintf> with C<"%.6f">, or the
234C<gettimeofday()> function in list context, which will give you the
235seconds and microseconds as two separate values.
389199d8 236
dcf686c9
JH
237=item sleep ( $floating_seconds )
238
f7916ddb 239Sleeps for the specified amount of seconds. Returns the number of
64a7a97c
RGS
240seconds actually slept (a floating point value). This function can
241be imported, resulting in a nice drop-in replacement for the C<sleep>
6937b144 242provided with perl, see the L</EXAMPLES> below.
dcf686c9 243
993164ab 244Note that the interaction between alarms and sleeps is unspecified.
64a7a97c 245
dcf686c9
JH
246=item alarm ( $floating_seconds [, $interval_floating_seconds ] )
247
6937b144
MJD
248The C<SIGALRM> signal is sent after the specified number of seconds.
249Implemented using C<ualarm()>. The C<$interval_floating_seconds> argument
250is optional and will be zero if unspecified, resulting in C<alarm()>-like
dcf686c9 251behaviour. This function can be imported, resulting in a nice drop-in
6937b144 252replacement for the C<alarm> provided with perl, see the L</EXAMPLES> below.
dcf686c9 253
64a7a97c
RGS
254B<NOTE 1>: With some combinations of operating systems and Perl
255releases C<SIGALRM> restarts C<select()>, instead of interrupting it.
256This means that an C<alarm()> followed by a C<select()> may together
257take the sum of the times specified for the the C<alarm()> and the
258C<select()>, not just the time of the C<alarm()>.
259
993164ab 260Note that the interaction between alarms and sleeps is unspecified.
3f2ee006 261
6937b144 262=item setitimer ( $which, $floating_seconds [, $interval_floating_seconds ] )
3c72ec00 263
09fa32a4 264Start up an interval timer: after a certain time, a signal arrives,
64a7a97c
RGS
265and more signals may keep arriving at certain intervals. To disable
266an "itimer", use C<$floating_seconds> of zero. If the
267C<$interval_floating_seconds> is set to zero (or unspecified), the
268timer is disabled B<after> the next delivered signal.
3c72ec00 269
6937b144
MJD
270Use of interval timers may interfere with C<alarm()>, C<sleep()>,
271and C<usleep()>. In standard-speak the "interaction is unspecified",
0be47ac6 272which means that I<anything> may happen: it may work, it may not.
3c72ec00
JH
273
274In scalar context, the remaining time in the timer is returned.
275
276In list context, both the remaining time and the interval are returned.
277
4ed0e2d4
RGS
278There are usually three or four interval timers available: the
279C<$which> can be C<ITIMER_REAL>, C<ITIMER_VIRTUAL>, C<ITIMER_PROF>, or
280C<ITIMER_REALPROF>. Note that which ones are available depends: true
281UNIX platforms usually have the first three, but (for example) Win32
282and Cygwin have only C<ITIMER_REAL>, and only Solaris seems to have
283C<ITIMER_REALPROF> (which is used to profile multithreaded programs).
3c72ec00 284
993164ab 285C<ITIMER_REAL> results in C<alarm()>-like behaviour. Time is counted in
6937b144 286I<real time>; that is, wallclock time. C<SIGALRM> is delivered when
3c72ec00
JH
287the timer expires.
288
4ed0e2d4
RGS
289C<ITIMER_VIRTUAL> counts time in (process) I<virtual time>; that is,
290only when the process is running. In multiprocessor/user/CPU systems
291this may be more or less than real or wallclock time. (This time is
292also known as the I<user time>.) C<SIGVTALRM> is delivered when the
293timer expires.
3c72ec00 294
6937b144 295C<ITIMER_PROF> counts time when either the process virtual time or when
0be47ac6
JH
296the operating system is running on behalf of the process (such as I/O).
297(This time is also known as the I<system time>.) (The sum of user
6937b144
MJD
298time and system time is known as the I<CPU time>.) C<SIGPROF> is
299delivered when the timer expires. C<SIGPROF> can interrupt system calls.
3c72ec00
JH
300
301The semantics of interval timers for multithreaded programs are
302system-specific, and some systems may support additional interval
6937b144 303timers. See your C<setitimer()> documentation.
3c72ec00
JH
304
305=item getitimer ( $which )
306
6937b144 307Return the remaining time in the interval timer specified by C<$which>.
3c72ec00
JH
308
309In scalar context, the remaining time is returned.
310
311In list context, both the remaining time and the interval are returned.
6937b144 312The interval is always what you put in using C<setitimer()>.
3c72ec00 313
ced84e60
SP
314=item clock_gettime ( $which )
315
316Return as seconds the current value of the POSIX high resolution timer
317specified by C<$which>. All implementations that support POSIX high
318resolution timers are supposed to support at least the C<$which> value
319of C<CLOCK_REALTIME>, which is supposed to return results close to the
320results of C<gettimeofday>, or the number of seconds since 00:00:00:00
321January 1, 1970 Greenwich Mean Time (GMT). Do not assume that
322CLOCK_REALTIME is zero, it might be one, or something else.
323Another potentially useful (but not available everywhere) value is
324C<CLOCK_MONOTONIC>, which guarantees a monotonically increasing time
325value (unlike time(), which can be adjusted). See your system
326documentation for other possibly supported values.
327
328=item clock_getres ( $which )
329
330Return as seconds the resolution of the POSIX high resolution timer
331specified by C<$which>. All implementations that support POSIX high
332resolution timers are supposed to support at least the C<$which> value
170c5524
SP
333of C<CLOCK_REALTIME>, see L</clock_gettime>.
334
335=item clock_nanosleep ( $which, $seconds, $flags = 0)
336
337Sleeps for the number of seconds (1e9ths of a second) specified.
338Returns the number of seconds actually slept. The $which is the
339"clock id", as with clock_gettime() and clock_getres(). The flags
340default to zero but C<TIMER_ABSTIME> can specified (must be exported
341explicitly) which means that C<$nanoseconds> is not a time interval
342(as is the default) but instead an absolute time. Can sleep for more
343than one second. Can also sleep for zero seconds, which often works
344like a I<thread yield>. See also C<Time::HiRes::sleep()>,
345C<Time::HiRes::usleep()>, and C<Time::HiRes::nanosleep()>.
346
347Do not expect clock_nanosleep() to be exact down to one nanosecond.
348Getting even accuracy of one thousand nanoseconds is good.
349
350=item clock()
351
352Return as seconds the I<process time> (user + system time) spent by
353the process since the first call to clock() (the definition is B<not>
354"since the start of the process", though if you are lucky these times
355may be quite close to each other, depending on the system). What this
356means is that you probably need to store the result of your first call
357to clock(), and subtract that value from the following results of clock().
358
359The time returned also includes the process times of the terminated
360child processes for which wait() has been executed. This value is
361somewhat like the second value returned by the times() of core Perl,
362but not necessarily identical. Note that due to backward
ff7df920
SP
363compatibility limitations the returned value may wrap around at about
3642147 seconds or at about 36 minutes.
ced84e60 365
75d5269b
SP
366=item stat
367
368=item stat FH
369
370=item stat EXPR
371
372As L<perlfunc/stat> but with the access/modify/change file timestamps
373in subsecond resolution, if the operating system and the filesystem
374both support such timestamps. To override the standard stat():
375
376 use Time::HiRes qw(stat);
377
378Test for the value of &Time::HiRes::d_hires_stat to find out whether
379the operating system supports subsecond file timestamps: a value
380larger than zero means yes. There are unfortunately no easy
381ways to find out whether the filesystem supports such timestamps.
c09e847b
SP
382UNIX filesystems often do; NTFS does; FAT doesn't (FAT timestamp
383granularity is B<two> seconds).
75d5269b
SP
384
385A zero return value of &Time::HiRes::d_hires_stat means that
386Time::HiRes::stat is a no-op passthrough for CORE::stat(),
387and therefore the timestamps will stay integers. The same
c09e847b
SP
388will happen if the filesystem does not do subsecond timestamps,
389even if the &Time::HiRes::d_hires_stat is non-zero.
75d5269b
SP
390
391In any case do not expect nanosecond resolution, or even a microsecond
392resolution.
393
dcf686c9
JH
394=back
395
396=head1 EXAMPLES
397
398 use Time::HiRes qw(usleep ualarm gettimeofday tv_interval);
399
400 $microseconds = 750_000;
70cf0185 401 usleep($microseconds);
dcf686c9
JH
402
403 # signal alarm in 2.5s & every .1s thereafter
70cf0185 404 ualarm(2_500_000, 100_000);
dcf686c9
JH
405
406 # get seconds and microseconds since the epoch
70cf0185 407 ($s, $usec) = gettimeofday();
dcf686c9
JH
408
409 # measure elapsed time
410 # (could also do by subtracting 2 gettimeofday return values)
411 $t0 = [gettimeofday];
412 # do bunch of stuff here
413 $t1 = [gettimeofday];
414 # do more stuff here
415 $t0_t1 = tv_interval $t0, $t1;
0be47ac6 416
dcf686c9
JH
417 $elapsed = tv_interval ($t0, [gettimeofday]);
418 $elapsed = tv_interval ($t0); # equivalent code
419
420 #
421 # replacements for time, alarm and sleep that know about
422 # floating seconds
423 #
424 use Time::HiRes;
425 $now_fractions = Time::HiRes::time;
426 Time::HiRes::sleep (2.5);
427 Time::HiRes::alarm (10.6666666);
0be47ac6 428
dcf686c9
JH
429 use Time::HiRes qw ( time alarm sleep );
430 $now_fractions = time;
431 sleep (2.5);
432 alarm (10.6666666);
433
3c72ec00
JH
434 # Arm an interval timer to go off first at 10 seconds and
435 # after that every 2.5 seconds, in process virtual time
436
437 use Time::HiRes qw ( setitimer ITIMER_VIRTUAL time );
438
36d6c396 439 $SIG{VTALRM} = sub { print time, "\n" };
3c72ec00
JH
440 setitimer(ITIMER_VIRTUAL, 10, 2.5);
441
1a7d3a53
SP
442 use Time::HiRes qw( clock_gettime clock_getres CLOCK_REALTIME );
443 # Read the POSIX high resolution timer.
444 my $high = clock_getres(CLOCK_REALTIME);
445 # But how accurate we can be, really?
446 my $reso = clock_getres(CLOCK_REALTIME);
ced84e60 447
170c5524
SP
448 use Time::HiRes qw( clock_nanosleep TIMER_ABSTIME );
449 clock_nanosleep(CLOCK_REALTIME, 1e6);
450 clock_nanosleep(CLOCK_REALTIME, 2e9, TIMER_ABSTIME);
451
452 use Time::HiRes qw( clock );
453 my $clock0 = clock();
454 ... # Do something.
455 my $clock1 = clock();
456 my $clockd = $clock1 - $clock0;
457
c09e847b
SP
458 use Time::HiRes qw( stat );
459 my ($atime, $mtime, $ctime) = (stat("istics"))[8, 9, 10];
460
dcf686c9
JH
461=head1 C API
462
463In addition to the perl API described above, a C API is available for
464extension writers. The following C functions are available in the
465modglobal hash:
466
467 name C prototype
468 --------------- ----------------------
469 Time::NVtime double (*)()
06252d99 470 Time::U2time void (*)(pTHX_ UV ret[2])
dcf686c9 471
6937b144
MJD
472Both functions return equivalent information (like C<gettimeofday>)
473but with different representations. The names C<NVtime> and C<U2time>
dcf686c9 474were selected mainly because they are operating system independent.
56c1b3bd
RGS
475(C<gettimeofday> is Unix-centric, though some platforms like Win32 and
476VMS have emulations for it.)
dcf686c9 477
6937b144 478Here is an example of using C<NVtime> from C:
dcf686c9 479
993164ab 480 double (*myNVtime)(); /* Returns -1 on failure. */
dcf686c9
JH
481 SV **svp = hv_fetch(PL_modglobal, "Time::NVtime", 12, 0);
482 if (!svp) croak("Time::HiRes is required");
483 if (!SvIOK(*svp)) croak("Time::NVtime isn't a function pointer");
356234a5 484 myNVtime = INT2PTR(double(*)(), SvIV(*svp));
dcf686c9
JH
485 printf("The current time is: %f\n", (*myNVtime)());
486
db0b859f
JH
487=head1 DIAGNOSTICS
488
34f69483
SP
489=head2 useconds or interval more than ...
490
491In ualarm() you tried to use number of microseconds or interval (also
492in microseconds) more than 1_000_000 and setitimer() is not available
493in your system to emulate that case.
494
db0b859f
JH
495=head2 negative time not invented yet
496
497You tried to use a negative time argument.
498
499=head2 internal error: useconds < 0 (unsigned ... signed ...)
500
501Something went horribly wrong-- the number of microseconds that cannot
502become negative just became negative. Maybe your compiler is broken?
503
f03b998d
JH
504=head1 CAVEATS
505
6937b144 506Notice that the core C<time()> maybe rounding rather than truncating.
d8cb5b61
RGS
507What this means is that the core C<time()> may be reporting the time
508as one second later than C<gettimeofday()> and C<Time::HiRes::time()>.
509
510Adjusting the system clock (either manually or by services like ntp)
511may cause problems, especially for long running programs that assume
512a monotonously increasing time (note that all platforms do not adjust
513time as gracefully as UNIX ntp does). For example in Win32 (and derived
514platforms like Cygwin and MinGW) the Time::HiRes::time() may temporarily
515drift off from the system clock (and the original time()) by up to 0.5
516seconds. Time::HiRes will notice this eventually and recalibrate.
ced84e60 517Note that since Time::HiRes 1.77 the clock_gettime(CLOCK_MONOTONIC)
1a7d3a53 518might help in this (in case your system supports CLOCK_MONOTONIC).
f03b998d 519
26e22fd9
RGS
520=head1 SEE ALSO
521
ced84e60
SP
522Perl modules L<BSD::Resource>, L<Time::TAI64>.
523
524Your system documentation for C<clock_gettime>, C<clock_settime>,
525C<gettimeofday>, C<getitimer>, C<setitimer>, C<ualarm>.
26e22fd9 526
dcf686c9
JH
527=head1 AUTHORS
528
529D. Wegscheid <wegscd@whirlpool.com>
530R. Schertler <roderick@argon.org>
531J. Hietaniemi <jhi@iki.fi>
532G. Aas <gisle@aas.no>
533
3f2ee006 534=head1 COPYRIGHT AND LICENSE
dcf686c9 535
3f2ee006 536Copyright (c) 1996-2002 Douglas E. Wegscheid. All rights reserved.
dcf686c9 537
f445b110 538Copyright (c) 2002, 2003, 2004, 2005, 2006 Jarkko Hietaniemi. All rights reserved.
dcf686c9 539
3f2ee006
HS
540This program is free software; you can redistribute it and/or modify
541it under the same terms as Perl itself.
dcf686c9
JH
542
543=cut