timer_getoverrun

       (REALTIME)

SYNOPSIS
       #include <time.h>

       int timer_getoverrun(timer_t timerid);
       int timer_gettime(timer_t timerid, struct itimerspec *value);
       int timer_settime(timer_t timerid, int flags,
              const struct itimerspec *restrict value,
              struct itimerspec *restrict ovalue);


DESCRIPTION
       The timer_gettime() function shall store the amount of time  until  the
       specified  timer,  timerid,  expires  and the reload value of the timer
       into the space pointed to by the value argument. The it_value member of
       this  structure  shall  contain  the  amount  of  time before the timer
       expires, or zero if the timer is disarmed. This value  is  returned  as
       the  interval  until timer expiration, even if the timer was armed with
       absolute time. The it_interval member of value shall contain the reload
       value last set by timer_settime().

       The  timer_settime() function shall set the time until the next expira-
       tion of the timer specified by timerid from the it_value member of  the
       value  argument  and  arm  the timer if the it_value member of value is
       non-zero. If the specified timer was already armed when timer_settime()
       is  called, this call shall reset the time until next expiration to the
       value specified. If the it_value member of value  is  zero,  the  timer
       shall  be  disarmed.  The effect of disarming or resetting a timer with
       pending expiration notifications is unspecified.

       If the flag TIMER_ABSTIME is not set in the argument flags,  timer_set-
       time()  shall  behave as if the time until next expiration is set to be
       equal to the interval specified by the it_value member of  value.  That
       is,  the  timer shall expire in it_value nanoseconds from when the call
       is made. If the flag  TIMER_ABSTIME  is  set  in  the  argument  flags,
       timer_settime()  shall  behave  as if the time until next expiration is
       set to be equal to the difference between the absolute  time  specified
       by  the  it_value  member  of  value and the current value of the clock
       associated with timerid.  That is, the  timer  shall  expire  when  the
       clock  reaches  the value specified by the it_value member of value. If
       the specified time has already passed, the function shall  succeed  and
       the expiration notification shall be made.

       The  reload  value  of the timer shall be set to the value specified by
       the it_interval member of value. When a timer is armed with a  non-zero
       it_interval, a periodic (or repetitive) timer is specified.

       Time  values that are between two consecutive non-negative integer mul-
       tiples of the resolution of the specified timer shall be rounded up  to
       the  larger  multiple  of  the resolution. Quantization error shall not
       cause the timer to expire earlier than the rounded time value.

       If the argument ovalue is not NULL, the timer_settime() function  shall
       the  number  of  extra timer expirations that occurred between the time
       the signal  was  generated  (queued)  and  when  it  was  delivered  or
       accepted,  up to but not including an implementation-defined maximum of
       {DELAYTIMER_MAX}. If the number of such extra  expirations  is  greater
       than  or equal to {DELAYTIMER_MAX}, then the overrun count shall be set
       to {DELAYTIMER_MAX}. The value  returned  by  timer_getoverrun()  shall
       apply  to  the most recent expiration signal delivery or acceptance for
       the timer.  If no expiration signal has been delivered for  the  timer,
       or if the Realtime Signals Extension is not supported, the return value
       of timer_getoverrun() is unspecified.

RETURN VALUE
       If the timer_getoverrun() function succeeds, it shall return the  timer
       expiration overrun count as explained above.

       If the timer_gettime() or timer_settime() functions succeed, a value of
       0 shall be returned.

       If an error occurs for any of these functions, the value  -1  shall  be
       returned, and errno set to indicate the error.

ERRORS
       The  timer_getoverrun(), timer_gettime(), and timer_settime() functions
       shall fail if:

       EINVAL The timerid argument does not correspond to an  ID  returned  by
              timer_create() but not yet deleted by timer_delete().


       The timer_settime() function shall fail if:

       EINVAL A value structure specified a nanosecond value less than zero or
              greater than or equal to 1000 million, and the  it_value  member
              of that structure did not specify zero seconds and nanoseconds.


       The following sections are informative.

EXAMPLES
       None.

APPLICATION USAGE
       None.

RATIONALE
       Practical  clocks  tick  at  a finite rate, with rates of 100 hertz and
       1000 hertz being common. The inverse of this tick  rate  is  the  clock
       resolution,  also called the clock granularity, which in either case is
       expressed as a time duration, being 10 milliseconds and  1  millisecond
       respectively  for  these  common  rates.   The granularity of practical
       clocks implies that if one reads a given clock twice in  rapid  succes-
       sion,  one may get the same time value twice; and that timers must wait
       for the next clock tick  after  the  theoretical  expiration  time,  to
       ensure  that  a timer never returns too soon. Note also that the granu-

FUTURE DIRECTIONS
       None.

SEE ALSO
       clock_getres() ,  timer_create()  ,  the  Base  Definitions  volume  of
       IEEE Std 1003.1-2001, <time.h>

COPYRIGHT
       Portions  of  this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
       --  Portable  Operating  System  Interface (POSIX), The Open Group Base
       Specifications Issue 6, Copyright (C) 2001-2003  by  the  Institute  of
       Electrical  and  Electronics  Engineers, Inc and The Open Group. In the
       event of any discrepancy between this version and the original IEEE and
       The  Open Group Standard, the original IEEE and The Open Group Standard
       is the referee document. The original Standard can be  obtained  online
       at http://www.opengroup.org/unix/online.html .



IEEE/The Open Group                  2003                  TIMER_GETOVERRUN(P)