time::hires.3

视频监控网络部分的协议ddns,的模块的实现代码,请大家大胆指正.

.ie n .IP "alarm ( $floating_seconds\fR [, \f(CW$interval_floating_seconds ] )" 4
.el .IP "alarm ( \f(CW$floating_seconds\fR [, \f(CW$interval_floating_seconds\fR ] )" 4
.IX Item "alarm ( $floating_seconds [, $interval_floating_seconds ] )"
The \f(CW\*(C`SIGALRM\*(C'\fR signal is sent after the specified number of seconds.
Implemented using \f(CW\*(C`ualarm()\*(C'\fR.  The \f(CW$interval_floating_seconds\fR argument
is optional and will be zero if unspecified, resulting in \f(CW\*(C`alarm()\*(C'\fR\-like
behaviour.  This function can be imported, resulting in a nice drop-in
replacement for the \f(CW\*(C`alarm\*(C'\fR provided with perl, see the \*(L"\s-1EXAMPLES\s0\*(R" below.
.Sp
\&\fB\s-1NOTE\s0 1\fR: With some combinations of operating systems and Perl
releases \f(CW\*(C`SIGALRM\*(C'\fR restarts \f(CW\*(C`select()\*(C'\fR, instead of interrupting it.
This means that an \f(CW\*(C`alarm()\*(C'\fR followed by a \f(CW\*(C`select()\*(C'\fR may together
take the sum of the times specified for the the \f(CW\*(C`alarm()\*(C'\fR and the
\&\f(CW\*(C`select()\*(C'\fR, not just the time of the \f(CW\*(C`alarm()\*(C'\fR.
.Sp
Note that the interaction between alarms and sleeps is unspecified.
.ie n .IP "setitimer ( $which\fR, \f(CW$floating_seconds\fR [, \f(CW$interval_floating_seconds ] )" 4
.el .IP "setitimer ( \f(CW$which\fR, \f(CW$floating_seconds\fR [, \f(CW$interval_floating_seconds\fR ] )" 4
.IX Item "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 \*(L"itimer\*(R", use \f(CW$floating_seconds\fR of zero.  If the
\&\f(CW$interval_floating_seconds\fR is set to zero (or unspecified), the
timer is disabled \fBafter\fR the next delivered signal.
.Sp
Use of interval timers may interfere with \f(CW\*(C`alarm()\*(C'\fR, \f(CW\*(C`sleep()\*(C'\fR,
and \f(CW\*(C`usleep()\*(C'\fR.  In standard-speak the \*(L"interaction is unspecified\*(R",
which means that \fIanything\fR may happen: it may work, it may not.
.Sp
In scalar context, the remaining time in the timer is returned.
.Sp
In list context, both the remaining time and the interval are returned.
.Sp
There are usually three or four interval timers (signals) available: the
\&\f(CW$which\fR can be \f(CW\*(C`ITIMER_REAL\*(C'\fR, \f(CW\*(C`ITIMER_VIRTUAL\*(C'\fR, \f(CW\*(C`ITIMER_PROF\*(C'\fR, or
\&\f(CW\*(C`ITIMER_REALPROF\*(C'\fR.  Note that which ones are available depends: true
\&\s-1UNIX\s0 platforms usually have the first three, but (for example) Win32
and Cygwin have only \f(CW\*(C`ITIMER_REAL\*(C'\fR, and only Solaris seems to have
\&\f(CW\*(C`ITIMER_REALPROF\*(C'\fR (which is used to profile multithreaded programs).
.Sp
\&\f(CW\*(C`ITIMER_REAL\*(C'\fR results in \f(CW\*(C`alarm()\*(C'\fR\-like behaviour.  Time is counted in
\&\fIreal time\fR; that is, wallclock time.  \f(CW\*(C`SIGALRM\*(C'\fR is delivered when
the timer expires.
.Sp
\&\f(CW\*(C`ITIMER_VIRTUAL\*(C'\fR counts time in (process) \fIvirtual time\fR; 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 \fIuser time\fR.)  \f(CW\*(C`SIGVTALRM\*(C'\fR is delivered when the
timer expires.
.Sp
\&\f(CW\*(C`ITIMER_PROF\*(C'\fR 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 \fIsystem time\fR.)  (The sum of user
time and system time is known as the \fI\s-1CPU\s0 time\fR.)  \f(CW\*(C`SIGPROF\*(C'\fR is
delivered when the timer expires.  \f(CW\*(C`SIGPROF\*(C'\fR can interrupt system calls.
.Sp
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 \f(CW\*(C`setitimer()\*(C'\fR documentation.
.ie n .IP "getitimer ( $which )" 4
.el .IP "getitimer ( \f(CW$which\fR )" 4
.IX Item "getitimer ( $which )"
Return the remaining time in the interval timer specified by \f(CW$which\fR.
.Sp
In scalar context, the remaining time is returned.
.Sp
In list context, both the remaining time and the interval are returned.
The interval is always what you put in using \f(CW\*(C`setitimer()\*(C'\fR.
.ie n .IP "clock_gettime ( $which )" 4
.el .IP "clock_gettime ( \f(CW$which\fR )" 4
.IX Item "clock_gettime ( $which )"
Return as seconds the current value of the \s-1POSIX\s0 high resolution timer
specified by \f(CW$which\fR.  All implementations that support \s-1POSIX\s0 high
resolution timers are supposed to support at least the \f(CW$which\fR value
of \f(CW\*(C`CLOCK_REALTIME\*(C'\fR, which is supposed to return results close to the
results of \f(CW\*(C`gettimeofday\*(C'\fR, or the number of seconds since 00:00:00:00
January 1, 1970 Greenwich Mean Time (\s-1GMT\s0).  Do not assume that
\&\s-1CLOCK_REALTIME\s0 is zero, it might be one, or something else.
Another potentially useful (but not available everywhere) value is
\&\f(CW\*(C`CLOCK_MONOTONIC\*(C'\fR, which guarantees a monotonically increasing time
value (unlike \fItime()\fR, which can be adjusted).  See your system
documentation for other possibly supported values.
.ie n .IP "clock_getres ( $which )" 4
.el .IP "clock_getres ( \f(CW$which\fR )" 4
.IX Item "clock_getres ( $which )"
Return as seconds the resolution of the \s-1POSIX\s0 high resolution timer
specified by \f(CW$which\fR.  All implementations that support \s-1POSIX\s0 high
resolution timers are supposed to support at least the \f(CW$which\fR value
of \f(CW\*(C`CLOCK_REALTIME\*(C'\fR, see \*(L"clock_gettime\*(R".
.ie n .IP "clock_nanosleep ( $which\fR, \f(CW$nanoseconds\fR, \f(CW$flags = 0)" 4
.el .IP "clock_nanosleep ( \f(CW$which\fR, \f(CW$nanoseconds\fR, \f(CW$flags\fR = 0)" 4
.IX Item "clock_nanosleep ( $which, $nanoseconds, $flags = 0)"
Sleeps for the number of nanoseconds (1e9ths of a second) specified.
Returns the number of nanoseconds actually slept.  The \f(CW$which\fR is the
\&\*(L"clock id\*(R", as with \fIclock_gettime()\fR and \fIclock_getres()\fR.  The flags
default to zero but \f(CW\*(C`TIMER_ABSTIME\*(C'\fR can specified (must be exported
explicitly) which means that \f(CW$nanoseconds\fR 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 \fIthread yield\fR.  See also \f(CW\*(C`Time::HiRes::sleep()\*(C'\fR,
\&\f(CW\*(C`Time::HiRes::usleep()\*(C'\fR, and \f(CW\*(C`Time::HiRes::nanosleep()\*(C'\fR.
.Sp
Do not expect \fIclock_nanosleep()\fR to be exact down to one nanosecond.
Getting even accuracy of one thousand nanoseconds is good.
.IP "\fIclock()\fR" 4
.IX Item "clock()"
Return as seconds the \fIprocess time\fR (user + system time) spent by
the process since the first call to \fIclock()\fR (the definition is \fBnot\fR
\&\*(L"since the start of the process\*(R", 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 \fIclock()\fR, and subtract that value from the following results of \fIclock()\fR.
.Sp
The time returned also includes the process times of the terminated
child processes for which \fIwait()\fR has been executed.  This value is
somewhat like the second value returned by the \fItimes()\fR 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.
.IP "stat" 4
.IX Item "stat"
.PD 0
.IP "stat \s-1FH\s0" 4
.IX Item "stat FH"
.IP "stat \s-1EXPR\s0" 4
.IX Item "stat EXPR"
.PD
As \*(L"stat\*(R" 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 \fIstat()\fR:
.Sp
.Vb 1
\&    use Time::HiRes qw(stat);
.Ve
.Sp
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.
\&\s-1UNIX\s0 filesystems often do; \s-1NTFS\s0 does; \s-1FAT\s0 doesn't (\s-1FAT\s0 timestamp
granularity is \fBtwo\fR seconds).
.Sp
A zero return value of &Time::HiRes::d_hires_stat means that
Time::HiRes::stat is a no-op passthrough for \fICORE::stat()\fR,
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.
.Sp
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
.Sp
.Vb 4
\&    write
\&    stat # t1
\&    read
\&    stat # t2
.Ve
.Sp
the access time stamp from t2 need not be greater-than the modify
time stamp from t1: it may be equal or \fIless\fR.
.SH "EXAMPLES"
.IX Header "EXAMPLES"
.Vb 1
\&  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, "\en" };
\&  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 \- $clock0;
\&
\&  use Time::HiRes qw( stat );
\&  my ($atime, $mtime, $ctime) = (stat("istics"))[8, 9, 10];
.Ve
.SH "C API"
.IX Header "C API"
In addition to the perl \s-1API\s0 described above, a C \s-1API\s0 is available for
extension writers.  The following C functions are available in the
modglobal hash:
.PP
.Vb 4
\&  name             C prototype
\&  \-\-\-\-\-\-\-\-\-\-\-\-\-\-\-  \-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-
\&  Time::NVtime     double (*)()
\&  Time::U2time     void (*)(pTHX_ UV ret[2])
.Ve
.PP
Both functions return equivalent information (like \f(CW\*(C`gettimeofday\*(C'\fR)
but with different representations.  The names \f(CW\*(C`NVtime\*(C'\fR and \f(CW\*(C`U2time\*(C'\fR
were selected mainly because they are operating system independent.
(\f(CW\*(C`gettimeofday\*(C'\fR is Unix-centric, though some platforms like Win32 and
\&\s-1VMS\s0 have emulations for it.)
.PP
Here is an example of using \f(CW\*(C`NVtime\*(C'\fR from C:
.PP
.Vb 6
\&  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\*(Aqt a function pointer");
\&  myNVtime = INT2PTR(double(*)(), SvIV(*svp));
\&  printf("The current time is: %f\en", (*myNVtime)());
.Ve
.SH "DIAGNOSTICS"
.IX Header "DIAGNOSTICS"
.Sh "useconds or interval more than ..."
.IX Subsection "useconds or interval more than ..."
In \fIualarm()\fR you tried to use number of microseconds or interval (also
in microseconds) more than 1_000_000 and \fIsetitimer()\fR is not available
in your system to emulate that case.
.Sh "negative time not invented yet"
.IX Subsection "negative time not invented yet"
You tried to use a negative time argument.
.Sh "internal error: useconds < 0 (unsigned ... signed ...)"
.IX Subsection "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?
.SH "CAVEATS"
.IX Header "CAVEATS"
Notice that the core \f(CW\*(C`time()\*(C'\fR maybe rounding rather than truncating.
What this means is that the core \f(CW\*(C`time()\*(C'\fR may be reporting the time
as one second later than \f(CW\*(C`gettimeofday()\*(C'\fR and \f(CW\*(C`Time::HiRes::time()\*(C'\fR.
.PP
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 \s-1UNIX\s0 ntp does).  For example in Win32 (and derived
platforms like Cygwin and MinGW) the \fITime::HiRes::time()\fR may temporarily
drift off from the system clock (and the original \fItime()\fR)  by up to 0.5
seconds. Time::HiRes will notice this eventually and recalibrate.
Note that since Time::HiRes 1.77 the clock_gettime(\s-1CLOCK_MONOTONIC\s0)
might help in this (in case your system supports \s-1CLOCK_MONOTONIC\s0).
.SH "SEE ALSO"
.IX Header "SEE ALSO"
Perl modules BSD::Resource, Time::TAI64.
.PP
Your system documentation for \f(CW\*(C`clock\*(C'\fR, \f(CW\*(C`clock_gettime\*(C'\fR,
\&\f(CW\*(C`clock_getres\*(C'\fR, \f(CW\*(C`clock_nanosleep\*(C'\fR, \f(CW\*(C`clock_settime\*(C'\fR, \f(CW\*(C`getitimer\*(C'\fR,
\&\f(CW\*(C`gettimeofday\*(C'\fR, \f(CW\*(C`setitimer\*(C'\fR, \f(CW\*(C`sleep\*(C'\fR, \f(CW\*(C`stat\*(C'\fR, \f(CW\*(C`ualarm\*(C'\fR.
.SH "AUTHORS"
.IX Header "AUTHORS"
D. Wegscheid <[e-mail]>
R. Schertler <[e-mail]>
J. Hietaniemi <[e-mail]>
G. Aas <[e-mail]>
.SH "COPYRIGHT AND LICENSE"
.IX Header "COPYRIGHT AND LICENSE"
Copyright (c) 1996\-2002 Douglas E. Wegscheid.  All rights reserved.
.PP
Copyright (c) 2002, 2003, 2004, 2005, 2006, 2007 Jarkko Hietaniemi.  All rights reserved.
.PP
This program is free software; you can redistribute it and/or modify
it under the same terms as Perl itself.