.\" Copyright (c) 2009 Linux Foundation, written by Michael Kerrisk .\" .\" .\" %%%LICENSE_START(VERBATIM) .\" Permission is granted to make and distribute verbatim copies of this .\" manual provided the copyright notice and this permission notice are .\" preserved on all copies. .\" .\" Permission is granted to copy and distribute modified versions of this .\" manual under the conditions for verbatim copying, provided that the .\" entire resulting derived work is distributed under the terms of a .\" permission notice identical to this one. .\" .\" Since the Linux kernel and libraries are constantly changing, this .\" manual page may be incorrect or out-of-date. The author(s) assume no .\" responsibility for errors or omissions, or for damages resulting from .\" the use of the information contained herein. The author(s) may not .\" have taken the same level of care in the production of this manual, .\" which is licensed free of charge, as they might when working .\" professionally. .\" .\" Formatted or processed versions of this manual, if unaccompanied by .\" the source, must acknowledge the copyright and authors of this work. .\" %%%LICENSE_END .\" .TH TIMER_SETTIME 2 2017-09-15 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 .PP .BI "int timer_settime(timer_t " timerid ", int " flags , .BI " const struct itimerspec *" new_value , .BI " struct itimerspec *" old_value ); .BI "int timer_gettime(timer_t " timerid ", struct itimerspec *" curr_value ); .fi .PP Link with \fI\-lrt\fP. .PP .in -4n Feature Test Macro Requirements for glibc (see .BR feature_test_macros (7)): .in .PP .BR timer_settime (), .BR timer_gettime (): _POSIX_C_SOURCE\ >=\ 199309L .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 EXAMPLE See .BR timer_create (2). .SH SEE ALSO .BR timer_create (2), .BR timer_getoverrun (2), .BR time (7) .SH COLOPHON This page is part of release 4.16 of the Linux .I 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/.