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| .TH TIMER_SETTIME 2 2021-03-22 Linux "Linux Programmer's Manual" |
| .SH NAME |
| timer_settime, timer_gettime \- arm/disarm and fetch |
| state of POSIX per-process timer |
| .SH SYNOPSIS |
| .nf |
| .B #include <time.h> |
| .PP |
| .BI "int timer_settime(timer_t " timerid ", int " flags , |
| .BI " const struct itimerspec *restrict " new_value , |
| .BI " struct itimerspec *restrict " old_value ); |
| .BI "int timer_gettime(timer_t " timerid ", struct itimerspec *" curr_value ); |
| .fi |
| .PP |
| Link with \fI\-lrt\fP. |
| .PP |
| .RS -4 |
| Feature Test Macro Requirements for glibc (see |
| .BR feature_test_macros (7)): |
| .RE |
| .PP |
| .BR timer_settime (), |
| .BR timer_gettime (): |
| .nf |
| _POSIX_C_SOURCE >= 199309L |
| .fi |
| .SH DESCRIPTION |
| .BR timer_settime () |
| arms or disarms the timer identified by |
| .IR timerid . |
| The |
| .I new_value |
| argument is pointer to an |
| .I itimerspec |
| structure that specifies the new initial value and |
| the new interval for the timer. |
| The |
| .I itimerspec |
| structure is defined as follows: |
| .PP |
| .in +4n |
| .EX |
| struct timespec { |
| time_t tv_sec; /* Seconds */ |
| long tv_nsec; /* Nanoseconds */ |
| }; |
| |
| struct itimerspec { |
| struct timespec it_interval; /* Timer interval */ |
| struct timespec it_value; /* Initial expiration */ |
| }; |
| .EE |
| .in |
| .PP |
| Each of the substructures of the |
| .I itimerspec |
| structure is a |
| .I timespec |
| structure that allows a time value to be specified |
| in seconds and nanoseconds. |
| These time values are measured according to the clock |
| that was specified when the timer was created by |
| .BR timer_create (2). |
| .PP |
| If |
| .I new_value\->it_value |
| specifies a nonzero value (i.e., either subfield is nonzero), then |
| .BR timer_settime () |
| arms (starts) the timer, |
| setting it to initially expire at the given time. |
| (If the timer was already armed, |
| then the previous settings are overwritten.) |
| If |
| .I new_value\->it_value |
| specifies a zero value |
| (i.e., both subfields are zero), |
| then the timer is disarmed. |
| .PP |
| The |
| .I new_value\->it_interval |
| field specifies the period of the timer, in seconds and nanoseconds. |
| If this field is nonzero, then each time that an armed timer expires, |
| the timer is reloaded from the value specified in |
| .IR new_value\->it_interval . |
| If |
| .I new_value\->it_interval |
| specifies a zero value, |
| then the timer expires just once, at the time specified by |
| .IR it_value . |
| .PP |
| By default, the initial expiration time specified in |
| .I new_value\->it_value |
| is interpreted relative to the current time on the timer's |
| clock at the time of the call. |
| This can be modified by specifying |
| .B TIMER_ABSTIME |
| in |
| .IR flags , |
| in which case |
| .I new_value\->it_value |
| is interpreted as an absolute value as measured on the timer's clock; |
| that is, the timer will expire when the clock value reaches the |
| value specified by |
| .IR new_value\->it_value . |
| If the specified absolute time has already passed, |
| then the timer expires immediately, |
| and the overrun count (see |
| .BR timer_getoverrun (2)) |
| will be set correctly. |
| .\" By experiment: the overrun count is set correctly, for CLOCK_REALTIME. |
| .PP |
| If the value of the |
| .B CLOCK_REALTIME |
| clock is adjusted while an absolute timer based on that clock is armed, |
| then the expiration of the timer will be appropriately adjusted. |
| Adjustments to the |
| .B CLOCK_REALTIME |
| clock have no effect on relative timers based on that clock. |
| .\" Similar remarks might apply with respect to process and thread CPU time |
| .\" clocks, but these clocks are not currently (2.6.28) settable on Linux. |
| .PP |
| If |
| .I old_value |
| is not NULL, then it points to a buffer |
| that is used to return the previous interval of the timer (in |
| .IR old_value\->it_interval ) |
| and the amount of time until the timer |
| would previously have next expired (in |
| .IR old_value\->it_value ). |
| .PP |
| .BR timer_gettime () |
| returns the time until next expiration, and the interval, |
| for the timer specified by |
| .IR timerid , |
| in the buffer pointed to by |
| .IR curr_value . |
| The time remaining until the next timer expiration is returned in |
| .IR curr_value\->it_value ; |
| this is always a relative value, regardless of whether the |
| .BR TIMER_ABSTIME |
| flag was used when arming the timer. |
| If the value returned in |
| .IR curr_value\->it_value |
| is zero, then the timer is currently disarmed. |
| The timer interval is returned in |
| .IR curr_value\->it_interval . |
| If the value returned in |
| .IR curr_value\->it_interval |
| is zero, then this is a "one-shot" timer. |
| .SH RETURN VALUE |
| On success, |
| .BR timer_settime () |
| and |
| .BR timer_gettime () |
| return 0. |
| On error, \-1 is returned, and |
| .I errno |
| is set to indicate the error. |
| .SH ERRORS |
| These functions may fail with the following errors: |
| .TP |
| .B EFAULT |
| .IR new_value , |
| .IR old_value , |
| or |
| .I curr_value |
| is not a valid pointer. |
| .TP |
| .B EINVAL |
| .I timerid |
| is invalid. |
| .\" FIXME . eventually: invalid value in flags |
| .PP |
| .BR timer_settime () |
| may fail with the following errors: |
| .TP |
| .B EINVAL |
| .I new_value.it_value |
| is negative; or |
| .I new_value.it_value.tv_nsec |
| is negative or greater than 999,999,999. |
| .SH VERSIONS |
| These system calls are available since Linux 2.6. |
| .SH CONFORMING TO |
| POSIX.1-2001, POSIX.1-2008. |
| .SH EXAMPLES |
| See |
| .BR timer_create (2). |
| .SH SEE ALSO |
| .BR timer_create (2), |
| .BR timer_getoverrun (2), |
| .BR time (7) |