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Time::HiRes(3perl) Perl Programmers Reference Guide Time::HiRes(3perl)
NAME
Time::HiRes - High resolution alarm, sleep, gettimeofday, interval timers
SYNOPSIS
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...;
DESCRIPTION
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.
EXAMPLES
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];
C API
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)());
DIAGNOSTICS
useconds or interval more than ...
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.
negative time not invented yet
You tried to use a negative time argument.
internal error: useconds < 0 (unsigned ... signed ...)
Something went horribly wrong-- the number of microseconds that cannot become negative
just became negative. Maybe your compiler is broken?
useconds or uinterval equal to or more than 1000000
In some platforms it is not possible to get an alarm with subsecond resolution and later
than one second.
unimplemented in this platform
Some calls simply aren't available, real or emulated, on every platform.
CAVEATS
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.
SEE ALSO
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).
AUTHORS
D. Wegscheid <wegscd AT whirlpool.com> R. Schertler <roderick AT argon.org> J. Hietaniemi
<jhi AT iki.fi> G. Aas <gisle AT aas.no>
COPYRIGHT AND LICENSE
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 AT fysh.org>
This program is free software; you can redistribute it and/or modify it under the same
terms as Perl itself.
perl v5.34.0 2023-11-23 Time::HiRes(3perl)
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On Apache
Under GNU General Public License
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