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Time::HiRes(3pm)       Perl Programmers Reference Guide       Time::HiRes(3pm)




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".

           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.


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_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(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 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.


SEE ALSO

       Perl modules BSD::Resource(3), Time::TAI64(3).

       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.



perl v5.24.0                      2016-04-26                  Time::HiRes(3pm)

perl 5.24 - Generated Sat Nov 26 08:08:41 CST 2016
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