Provided by: perl-doc_5.28.1-6_all bug

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::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.

       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", "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.