timer_getoverrun(3p) — Linux manual page

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.

       The behavior is undefined if the value specified by the timerid
       argument to timer_getoverrun(), timer_gettime(), or
       timer_settime() does not correspond to a timer ID returned by
       timer_create() but not yet deleted by timer_delete().

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.

       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.1‐2017 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.

       If an implementation detects that the value specified by the
       timerid argument to timer_getoverrun(), timer_gettime(), or
       timer_settime() does not correspond to a timer ID returned by
       timer_create() but not yet deleted by timer_delete(), it is
       recommended that the function should fail and report an [EINVAL]
       error.

FUTURE DIRECTIONS         top

       None.

SEE ALSO         top

       clock_getres(3p), timer_create(3p)

       The Base Definitions volume of POSIX.1‐2017, time.h(0p)

COPYRIGHT         top

       Portions of this text are reprinted and reproduced in electronic
       form from IEEE Std 1003.1-2017, Standard for Information
       Technology -- Portable Operating System Interface (POSIX), The
       Open Group Base Specifications Issue 7, 2018 Edition, Copyright
       (C) 2018 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 .

       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               2017              TIMER_GETOVERRUN(3P)

Pages that refer to this page: time.h(0p)clock_getres(3p)getitimer(3p)timer_create(3p)