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

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 );

	 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
			     ITIMER_REAL ITIMER_VIRTUAL ITIMER_PROF ITIMER_REALPROF );

	 setitimer ($which, $floating_seconds, $floating_interval );
	 getitimer ($which);

	 $realtime   = clock_gettime(CLOCK_REALTIME);
	 $resolution = clock_getres(CLOCK_REALTIME);

	 clock_nanosleep(CLOCK_REALTIME, 1.5);
	 clock_nanosleep(CLOCK_REALTIME, time() + 10, TIMER_ABSTIME);

	 my $ticktock = clock();

DESCRIPTION
       The "Time::HiRes" module implements a Perl interface to the "usleep",
       "nanosleep", "ualarm", "gettimeofday", and "setitimer"/"getitimer" sys-
       tem calls, in other words, high resolution time and timers. See the
       "EXAMPLES" section below and the test scripts for usage; see your sys-
       tem 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 peculiar-
       ities.

       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.

       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) speci-
	   fied.  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.  Get-
	   ting 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.

	   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 near-
	   est 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 "ualarm()".  The $interval_floating_seconds argu-
	   ment 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.

	   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 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 arrives,
	   and more signals may keep arriving at certain intervals.  To dis-
	   able an "itimer", use $floating_seconds of zero.  If the $inter-
	   val_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 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 (for example)
	   Win32 and Cygwin have only "ITIMER_REAL", and only Solaris seems to
	   have "ITIMER_REALPROF" (which is used to profile multithreaded pro-
	   grams).

	   "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 sys-
	   tems 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 sys-
	   tem calls.

	   The semantics of interval timers for multithreaded programs are
	   system-specific, and some systems may support additional interval
	   timers.  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 some-
	   thing else.	Another potentially useful (but not available every-
	   where) value is "CLOCK_MONOTONIC", which guarantees a monotonically
	   increasing time value (unlike time(), 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, $seconds, $flags = 0)
	   Sleeps for the number of seconds (1e9ths of a second) specified.
	   Returns the number of seconds 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 fol-
	   lowing 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.

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);

	 # 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_getres(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;

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 mod-
       global 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.  ("get-
       timeofday" 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
       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?

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_get-
       time(CLOCK_MONOTONIC) might help in this (in case your system supports
       CLOCK_MONOTONIC).

SEE ALSO
       Perl modules BSD::Resource, Time::TAI64.

       Your system documentation for "clock_gettime", "clock_settime", "get-
       timeofday", "getitimer", "setitimer", "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 Jarkko Hietaniemi.	All rights
       reserved.

       This program is free software; you can redistribute it and/or modify it
       under the same terms as Perl itself.

perl v5.8.8			  2006-06-14			Time::HiRes(3)
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