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NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | VERSIONS | STANDARDS | HISTORY | BUGS | EXAMPLES | SEE ALSO | COLOPHON |
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timer_getoverrun(2) System Calls Manual timer_getoverrun(2)
timer_getoverrun - get overrun count for a POSIX per-process
timer
Real-time library (librt, -lrt)
#include <time.h>
int timer_getoverrun(timer_t timerid);
Feature Test Macro Requirements for glibc (see
feature_test_macros(7)):
timer_getoverrun():
_POSIX_C_SOURCE >= 199309L
timer_getoverrun() returns the "overrun count" for the timer
referred to by timerid. An application can use the overrun count
to accurately 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. 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 sigwaitinfo(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.
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.
EINVAL timerid is not a valid timer ID.
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.
POSIX.1 discusses timer overruns only in the context of timer
notifications using signals.
POSIX.1-2008.
Linux 2.6. POSIX.1-2001.
POSIX.1 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,
before Linux 4.19, if the timer overrun value exceeds the maximum
representable integer, the counter cycles, starting once more
from low values. Since Linux 4.19, timer_getoverrun() returns
DELAYTIMER_MAX (defined as INT_MAX in <limits.h>) in this case
(and the overrun value is reset to 0).
See timer_create(2).
clock_gettime(2), sigaction(2), signalfd(2), sigwaitinfo(2),
timer_create(2), timer_delete(2), timer_settime(2), signal(7),
time(7)
This page is part of the man-pages (Linux kernel and C library
user-space interface documentation) project. Information about
the project can be found at
⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report
for this manual page, see
⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
This page was obtained from the tarball man-pages-6.9.1.tar.gz
fetched from
⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
2024-06-26. If you discover any rendering problems in this HTML
version of the page, or you believe there is a better or more up-
to-date source for the page, or you have corrections or
improvements to the information in this COLOPHON (which is not
part of the original manual page), send a mail to
man-pages@man7.org
Linux man-pages 6.9.1 2024-05-02 timer_getoverrun(2)
Pages that refer to this page: sigaction(2), syscalls(2), timer_create(2), timer_delete(2), timerfd_create(2), timer_settime(2), timer_t(3type), ualarm(3), usleep(3), signal-safety(7)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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