man2/timer_settime.2

   1 .\" Copyright (c) 2009 Linux Foundation, written by Michael Kerrisk
   2 .\"     <mtk.manpages@gmail.com>
   3 .\"
   4 .\" %%%LICENSE_START(VERBATIM)
   5 .\" Permission is granted to make and distribute verbatim copies of this
   6 .\" manual provided the copyright notice and this permission notice are
   7 .\" preserved on all copies.
   8 .\"
   9 .\" Permission is granted to copy and distribute modified versions of this
  10 .\" manual under the conditions for verbatim copying, provided that the
  11 .\" entire resulting derived work is distributed under the terms of a
  12 .\" permission notice identical to this one.
  13 .\"
  14 .\" Since the Linux kernel and libraries are constantly changing, this
  15 .\" manual page may be incorrect or out-of-date.  The author(s) assume no
  16 .\" responsibility for errors or omissions, or for damages resulting from
  17 .\" the use of the information contained herein.  The author(s) may not
  18 .\" have taken the same level of care in the production of this manual,
  19 .\" which is licensed free of charge, as they might when working
  20 .\" professionally.
  21 .\"
  22 .\" Formatted or processed versions of this manual, if unaccompanied by
  23 .\" the source, must acknowledge the copyright and authors of this work.
  24 .\" %%%LICENSE_END
  25 .TH TIMER_SETTIME 2 2012-10-15 Linux "Linux Programmer's Manual"
  26 .SH NAME
  27 timer_settime, timer_gettime \- arm/disarm and fetch
  28 state of POSIX per-process timer
  29 .SH SYNOPSIS
  30 .nf
  31 .B  #include <time.h>
  32
  33 .BI "int timer_settime(timer_t " timerid ", int " flags ,
  34 .BI "                  const struct itimerspec *" new_value ,
  35 .BI "                  struct itimerspec * " old_value );
  36 .BI "int timer_gettime(timer_t " timerid ", struct itimerspec *" curr_value );
  37 .fi
  38
  39 Link with \fI\-lrt\fP.
  40 .sp
  41 .in -4n
  42 Feature Test Macro Requirements for glibc (see
  43 .BR feature_test_macros (7)):
  44 .in
  45 .sp
  46 .BR timer_settime (),
  47 .BR timer_gettime ():
  48 _POSIX_C_SOURCE\ >=\ 199309L
  49 .SH DESCRIPTION
  50 .BR timer_settime ()
  51 arms or disarms the timer identified by
  52 .IR timerid .
  53 The
  54 .I new_value
  55 argument is pointer to an
  56 .I itimerspec
  57 structure that specifies the new initial value and
  58 the new interval for the timer.
  59 The
  60 .I itimerspec
  61 structure is defined as follows:
  62
  63 .in +4n
  64 .nf
  65 struct timespec {
  66     time_t tv_sec;                /* Seconds */
  67     long   tv_nsec;               /* Nanoseconds */
  68 };
  69
  70 struct itimerspec {
  71     struct timespec it_interval;  /* Timer interval */
  72     struct timespec it_value;     /* Initial expiration */
  73 };
  74 .fi
  75 .in
  76
  77 Each of the substructures of the
  78 .I itimerspec
  79 structure is a
  80 .I timespec
  81 structure that allows a time value to be specified
  82 in seconds and nanoseconds.
  83 These time values are measured according to the clock
  84 that was specified when the timer was created by
  85 .BR timer_create (2)
  86
  87 If
  88 .I new_value->it_value
  89 specifies a nonzero value (i.e., either subfield is nonzero), then
  90 .BR timer_settime ()
  91 arms (starts) the timer,
  92 setting it to initially expire at the given time.
  93 (If the timer was already armed,
  94 then the previous settings are overwritten.)
  95 If
  96 .I new_value->it_value
  97 specifies a zero value
  98 (i.e., both subfields are zero),
  99 then the timer is disarmed.
 100
 101 The
 102 .I new_value->it_interval
 103 field specifies the period of the timer, in seconds and nanoseconds.
 104 If this field is nonzero, then each time that an armed timer expires,
 105 the timer is reloaded from the value specified in
 106 .IR new_value->it_interval .
 107 If
 108 .I new_value->it_interval
 109 specifies a zero value
 110 then the timer expires just once, at the time specified by
 111 .IR it_value .
 112
 113 By default, the initial expiration time specified in
 114 .I new_value->it_value
 115 is interpreted relative to the current time on the timer's
 116 clock at the time of the call.
 117 This can be modified by specifying
 118 .B TIMER_ABSTIME
 119 in
 120 .IR flags ,
 121 in which case
 122 .I new_value->it_value
 123 is interpreted as an absolute value as measured on the timer's clock;
 124 that is, the timer will expire when the clock value reaches the
 125 value specified by
 126 .IR new_value->it_value .
 127 If the specified absolute time has already passed,
 128 then the timer expires immediately,
 129 and the overrun count (see
 130 .BR timer_getoverrun (2))
 131 will be set correctly.
 132 .\" By experiment: the overrun count is set correctly, for CLOCK_REALTIME.
 133
 134 If the value of the
 135 .B CLOCK_REALTIME
 136 clock is adjusted while an absolute timer based on that clock is armed,
 137 then the expiration of the timer will be appropriately adjusted.
 138 Adjustments to the
 139 .B CLOCK_REALTIME
 140 clock have no effect on relative timers based on that clock.
 141 .\" Similar remarks might apply with respect to process and thread CPU time
 142 .\" clocks, but these clocks are not currently (2.6.28) settable on Linux.
 143
 144 If
 145 .I old_value
 146 is not NULL, then it points to a buffer
 147 that is used to return the previous interval of the timer (in
 148 .IR old_value->it_interval )
 149 and the amount of time until the timer
 150 would previously have next expired (in
 151 .IR old_value->it_value ).
 152
 153 .BR timer_gettime ()
 154 returns the time until next expiration, and the interval,
 155 for the timer specified by
 156 .IR timerid ,
 157 in the buffer pointed to by
 158 .IR curr_value .
 159 The time remaining until the next timer expiration is returned in
 160 .IR curr_value->it_value ;
 161 this is always a relative value, regardless of whether the
 162 .BR TIMER_ABSTIME
 163 flag was used when arming the timer.
 164 If the value returned in
 165 .IR curr_value->it_value
 166 is zero, then the timer is currently disarmed.
 167 The timer interval is returned in
 168 .IR curr_value->it_interval .
 169 If the value returned in
 170 .IR curr_value->it_interval
 171 is zero, then this is a "one-shot" timer.
 172 .SH RETURN VALUE
 173 On success,
 174 .BR timer_settime ()
 175 and
 176 .BR timer_gettime ()
 177 return 0.
 178 On error, \-1 is returned, and
 179 .I errno
 180 is set to indicate the error.
 181 .SH ERRORS
 182 These functions may fail with the following errors:
 183 .TP
 184 .B EFAULT
 185 .IR new_value ,
 186 .IR old_value ,
 187 or
 188 .I curr_value
 189 is not a valid pointer.
 190 .TP
 191 .B EINVAL
 192 .I timerid
 193 is invalid.
 194 .\" FIXME . eventually: invalid value in flags
 195 .PP
 196 .BR timer_settime ()
 197 may fail with the following errors:
 198 .TP
 199 .B EINVAL
 200 .I new_value.it_value
 201 is negative; or
 202 .I new_value.it_value.tv_nsec
 203 is negative or greater than 999,999,999.
 204 .SH VERSIONS
 205 These system calls are available since Linux 2.6.
 206 .SH CONFORMING TO
 207 POSIX.1-2001.
 208 .SH EXAMPLE
 209 See
 210 .BR timer_create (2).
 211 .SH SEE ALSO
 212 .BR timer_create (2),
 213 .BR timer_getoverrun (2),
 214 .BR time (7)