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TIMER_GETOVERRUN(P)        POSIX Programmer's Manual       TIMER_GETOVERRUN(P)

NAME
       timer_getoverrun,  timer_gettime,  timer_settime  -  per-process timers
       (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
       store,  in  the location referenced by ovalue, a value representing the
       previous amount of time before the timer would have expired, or zero if
       the  timer was disarmed, together with the previous timer reload value.
       Timers shall not expire before their scheduled time.

       Only a single signal shall be queued to the process for a  given  timer
       at  any point in time. When a timer for which a signal is still pending
       expires, no signal shall be queued, and a timer  overrun  shall  occur.
        When  a  timer expiration signal is delivered to or accepted by a pro-
       cess, if the implementation supports the  Realtime  Signals  Extension,
       the timer_getoverrun() function shall return the timer expiration over-
       run count for the specified timer. The overrun count returned  contains
       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-
       larity of the clock may be significantly coarser than the resolution of
       the data format used to set and get time and interval values. Also note
       that  some  implementations  may  choose to adjust time and/or interval
       values to exactly match the ticks of the underlying clock.

       This volume of IEEE Std 1003.1-2001 defines  functions  that  allow  an
       application  to  determine  the implementation-supported resolution for
       the clocks and requires an implementation to  document  the  resolution
       supported  for timers and nanosleep() if they differ from the supported
       clock resolution.  This is more of a procurement issue than  a  runtime
       application issue.

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)

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