PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT

TIMER_GETOVERRUN(3P)      POSIX Programmer's Manual     TIMER_GETOVERRUN(3P)

PROLOG         top

       This manual page is part of the POSIX Programmer's Manual.  The Linux
       implementation of this interface may differ (consult the
       corresponding Linux manual page for details of Linux behavior), or
       the interface may not be implemented on Linux.

NAME         top

       timer_getoverrun, timer_gettime, timer_settime — per-process timers

SYNOPSIS         top

       #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         top

       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
       expiration 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_settime() 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
       multiples 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 process, the timer_getoverrun() function shall return the timer
       expiration overrun 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, the return value of
       timer_getoverrun() is unspecified.

RETURN VALUE         top

       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         top

       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.

       These functions may 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 may fail if:

       EINVAL The it_interval member of value is not zero and the timer was
              created with notification by creation of a new thread
              (sigev_sigev_notify was SIGEV_THREAD) and a fixed stack
              address has been set in the thread attribute pointed to by
              sigev_notify_attributes.

       The following sections are informative.

EXAMPLES         top

       None.

APPLICATION USAGE         top

       Using fixed stack addresses is problematic when timer expiration is
       signaled by the creation of a new thread. Since it cannot be assumed
       that the thread created for one expiration is finished before the
       next expiration of the timer, it could happen that two threads use
       the same memory as a stack at the same time. This is invalid and
       produces undefined results.

RATIONALE         top

       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 succession, 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 granularity 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 POSIX.1‐2008 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         top

       None.

SEE ALSO         top

       clock_getres(3p), timer_create(3p)

       The Base Definitions volume of POSIX.1‐2008, time.h(0p)

COPYRIGHT         top

       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information
       Technology -- Portable Operating System Interface (POSIX), The Open
       Group Base Specifications Issue 7, Copyright (C) 2013 by the
       Institute of Electrical and Electronics Engineers, Inc and The Open
       Group.  (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1
       applied.) 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.unix.org/online.html .

       Any typographical or formatting errors that appear in this page are
       most likely to have been introduced during the conversion of the
       source files to man page format. To report such errors, see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group                 2013                TIMER_GETOVERRUN(3P)