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 );
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");
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::usleep()", "Time::HiRes::sleep()", and
"Time::HiRes::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
"Time::HiRes::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()" 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".
- 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.
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 double (*)()
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:
double (*myNVtime)(); /* Returns -1 on failure. */
SV **svp = hv_fetch(PL_modglobal, "Time::NVtime", 12, 0);
if (!svp) croak("Time::HiRes is required");
if (!SvIOK(*svp)) croak("Time::NVtime isn't a function pointer");
myNVtime = INT2PTR(double(*)(), SvIV(*svp));
printf("The current time is: %f\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.
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.
SEE ALSO¶
Perl modules BSD::Resource, Time::TAI64.
Your system documentation for "clock", "clock_gettime",
"clock_getres", "clock_nanosleep",
"clock_settime", "getitimer", "gettimeofday",
"setitimer", "sleep", "stat",
"ualarm".
AUTHORS¶
D. Wegscheid <wegscd@whirlpool.com> R. Schertler
<roderick@argon.org> J. Hietaniemi <jhi@iki.fi> G. Aas
<gisle@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@fysh.org>
This program is free software; you can redistribute it and/or modify it under
the same terms as Perl itself.