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home | helpx minix x x minixx 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 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.) Be- cause of system scheduling delays, or because the signal may be tempo- rarily blocked, there can be a delay between the time when the notifi- cation 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 over- run count is the number of additional timer expirations that occurred between the time when the signal was generated and when it was deliv- ered or accepted. Timer overruns can also occur when expiration notifications are deliv- ered via invocation of a thread, since there may be an arbitrary delay between an expiration of the timer and the invocation of the notifica- tion thread, and in that delay interval, additional timer expirations may occur. RETURN VALUE On success, timer_getoverrun() returns the overrun count of the speci- fied timer; this count may be 0 if no overruns have occurred. On fail- ure, -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, POSIX.1-2008. NOTES When timer notifications are delivered via signals (SIGEV_SIGNAL), on Linux it is also possible to obtain the overrun count via the si_over- run 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 notifica- tions using signals. BUGS 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, 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_cre- ate(2), timer_delete(2), timer_settime(2), signal(7), time(7) COLOPHON This page is part of release 5.05 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man-pages/. Linux 2017-09-15 TIMER_GETOVERRUN(2)
NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | VERSIONS | CONFORMING TO | NOTES | BUGS | EXAMPLE | SEE ALSO | COLOPHON