TIMER_GETOVERRUN(2)					     Linux Programmer's Manual					       TIMER_GETOVERRUN(2)

NAME

       timer_getoverrun - get overrun count for a POSIX per-process timer

SYNOPSIS

       #include <time.h>

       int timer_getoverrun(timer_t timerid);

       Link with -lrt.

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       timer_getoverrun(): _POSIX_C_SOURCE >= 199309L

DESCRIPTION

       timer_getoverrun()  returns  the  "overrun  count" for the timer referred to by timerid.  An application can use the overrun count to accu-
       rately calculate the number of timer expirations that would have occurred over a given time interval.  Timer overruns can occur	both  when
       receiving expiration notifications via signals (SIGEV_SIGNAL), and via threads (SIGEV_THREAD).

       When  expiration  notifications are delivered via a signal, overruns can occur as follows.  Regardless of whether or not a real-time signal
       is used for timer notifications, the system queues at most one signal per timer.  (This is the behavior	specified  by  POSIX.1-2001.   The
       alternative,  queuing one signal for each timer expiration, could easily result in overflowing the allowed limits for queued signals on the
       system.)  Because of system scheduling delays, or because the signal may be temporarily blocked, there can be a delay between the time when
       the notification signal is generated and the time when it is delivered (e.g., caught by a signal handler) or accepted (e.g., using sigwait-
       info(2)).  In this interval, further timer expirations may occur.  The timer overrun count is the number of  additional	timer  expirations
       that occurred between the time when the signal was generated and when it was delivered or accepted.

       Timer overruns can also occur when expiration notifications are delivered via invocation of a thread, since there may be an arbitrary delay
       between an expiration of the timer and the invocation of the notification thread, and in that delay interval, additional timer  expirations
       may occur

RETURN VALUE

       On  success,  timer_getoverrun()  returns  the  overrun count of the specified timer; this count may be 0 if no overruns have occurred.	On
       failure, -1 is returned, and errno is set to indicate the error.

ERRORS

       EINVAL timerid is not a valid timer ID.

VERSIONS

       This system call is available since Linux 2.6.

CONFORMING TO

       POSIX.1-2001

NOTES

       When timer notifications are delivered via signals (SIGEV_SIGNAL), on Linux it is also  possible  to  obtain  the  overrun  count  via  the
       si_overrun  field  of the siginfo_t structure (see sigaction(2)).  This allows an application to avoid the overhead of making a system call
       to obtain the overrun count, but is a nonportable extension to POSIX.1-2001.

       POSIX.1-2001 only discusses timer overruns in the context of timer notifications using signals.

BUGS

       POSIX.1-2001 specifies that if the timer overrun count is equal to or greater than an implementation-defined maximum, DELAYTIMER_MAX,  then
       timer_getoverrun()  should  return  DELAYTIMER_MAX.   However,  Linux  does not implement this feature: instead, if the timer overrun value
       exceeds the maximum representable integer, the counter cycles, starting once more from low values.

EXAMPLE

       See timer_create(2).

SEE ALSO

       clock_gettime(2), sigaction(2), signalfd(2), sigwaitinfo(2), timer_create(2), timer_delete(2), timer_settime(2), signal(7), time(7)

COLOPHON

       This page is part of release 3.27 of the Linux man-pages project.  A description of the project, and information about reporting bugs,  can
       be found at http://www.kernel.org/doc/man-pages/.

Linux								    2009-02-20						       TIMER_GETOVERRUN(2)