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PROLOG |NAME |SYNOPSIS |DESCRIPTION |RETURN VALUE |ERRORS |EXAMPLES |APPLICATION USAGE |RATIONALE |FUTURE DIRECTIONS |SEE ALSO |COPYRIGHT | |
TIMER_GETOVERRUN(3P) POSIX Programmer's ManualTIMER_GETOVERRUN(3P)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.
timer_getoverrun, timer_gettime, timer_settime — per-process timers
#include <time.h> int timer_getoverrun(timer_ttimerid); int timer_gettime(timer_ttimerid, struct itimerspec *value); int timer_settime(timer_ttimerid, intflags, const struct itimerspec *restrictvalue, struct itimerspec *restrictovalue);
Thetimer_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 thevalue argument. Theit_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. Theit_interval member ofvalue shall contain the reload value last set bytimer_settime(). Thetimer_settime() function shall set the time until the next expiration of the timer specified bytimerid from theit_value member of thevalue argument and arm the timer if theit_value member ofvalue is non-zero. If the specified timer was already armed whentimer_settime() is called, this call shall reset the time until next expiration to thevalue specified. If theit_value member ofvalue 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 argumentflags,timer_settime() shall behave as if the time until next expiration is set to be equal to the interval specified by theit_value member ofvalue. That is, the timer shall expire init_value nanoseconds from when the call is made. If the flag TIMER_ABSTIME is set in the argumentflags,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 theit_value member ofvalue and the current value of the clock associated withtimerid. That is, the timer shall expire when the clock reaches the value specified by theit_value member ofvalue. 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 theit_interval member ofvalue. When a timer is armed with a non-zeroit_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 argumentovalue is not NULL, thetimer_settime() function shall store, in the location referenced byovalue, 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, thetimer_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 bytimer_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 oftimer_getoverrun() is unspecified. The behavior is undefined if the value specified by thetimerid argument totimer_getoverrun(),timer_gettime(), ortimer_settime() does not correspond to a timer ID returned bytimer_create() but not yet deleted bytimer_delete().If thetimer_getoverrun() function succeeds, it shall return the timer expiration overrun count as explained above. If thetimer_gettime() ortimer_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, anderrno set to indicate the error.
Thetimer_settime() function shall fail if:EINVALAvalue structure specified a nanosecond value less than zero or greater than or equal to 1000 million, and theit_value member of that structure did not specify zero seconds and nanoseconds. Thetimer_settime() function may fail if:EINVALTheit_interval member ofvalue 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 bysigev_notify_attributes.The following sections are informative.
None.
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.
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 andnanosleep() 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 thetimerid argument totimer_getoverrun(),timer_gettime(), ortimer_settime() does not correspond to a timer ID returned bytimer_create() but not yet deleted bytimer_delete(), it is recommended that the function should fail and report an[EINVAL] error.
None.
clock_getres(3p),timer_create(3p) The Base Definitions volume of POSIX.1‐2017,time.h(0p)
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 athttp://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, seehttps://www.kernel.org/doc/man-pages/reporting_bugs.html .IEEE/The Open Group 2017TIMER_GETOVERRUN(3P)Pages that refer to this page:time.h(0p), clock_getres(3p), getitimer(3p), timer_create(3p)
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