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HiRes(3) |
User Contributed Perl Documentation |
HiRes(3) |
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.
- 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::sleep()", and
"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
"clock_nanosleep()".
Do not expect nanosleep() to be exact down to one
nanosecond. Getting even accuracy of one thousand 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.
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.
- 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
"gettimeofday()". 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 (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.
- 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
"setitimer()" if available,
"ualarm()" if not. 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 replacement for the
"alarm" provided with perl, see the
"EXAMPLES" below.
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.
- setitimer ( $which, $floating_seconds [, $interval_floating_seconds ]
)
- Start up an interval timer: after a certain time, a signal ($which)
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 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.
- 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() or
gettimeofday(), which can be adjusted). See your system
documentation 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".
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.
- clock_nanosleep ( $which, $nanoseconds, $flags = 0)
- Sleeps for the number of nanoseconds (1e9ths of a second) specified.
Returns the number of nanoseconds 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.
- stat
- stat FH
- stat EXPR
- lstat
- lstat FH
- lstat EXPR
- As "stat" in perlfunc or "lstat" in perlfunc but with
the access/modify/change file timestamps in subsecond resolution, if the
operating system and the filesystem both support such timestamps. To
override the standard stat():
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.
- utime LIST
- As "utime" in perlfunc but with the ability to set the
access/modify file timestamps in subsecond resolution, if the operating
system and the filesystem, and the mount options of the filesystem, all
support such timestamps.
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.
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