man2/timer_settime.2

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  23 .TH TIMER_SETTIME 2 2009-02-16 Linux "Linux Programmer's Manual"
  24 .SH NAME
  25 timer_settime, timer_gettime \- arm/disarm and fetch
  26 state of POSIX per-process timer
  27 .SH SYNOPSIS
  28 .nf
  29 .B  #include <time.h>
  30
  31 .BI "int timer_settime(timer_t " timerid ", int " flags ,
  32 .BI "                  const struct itimerspec *" new_value ,
  33 .BI "                  struct itimerspec * " old_value );
  34 .BI "int timer_gettime(timer_t " timerid ", struct itimerspec *" curr_value );
  35 .fi
  36
  37 Link with
  38 .IR \-lrt .
  39 .sp
  40 .in -4n
  41 Feature Test Macro Requirements for glibc (see
  42 .BR feature_test_macros (7)):
  43 .in
  44 .sp
  45 .BR timer_settime (),
  46 .BR timer_gettime ():
  47 _POSIX_C_SOURCE >= 199309
  48 .SH DESCRIPTION
  49 .BR timer_settime ()
  50 arms or disarms the timer identified by
  51 .IR timerid .
  52 The
  53 .I new_value
  54 argument is an
  55 .I itimerspec
  56 structure that specifies the new initial value and
  57 the new interval for the timer.
  58 The
  59 .I itimerspec
  60 structure is defined as follows:
  61
  62 .in +4n
  63 .nf
  64 struct timespec {
  65     time_t tv_sec;                /* Seconds */
  66     long   tv_nsec;               /* Nanoseconds */
  67 };
  68
  69 struct itimerspec {
  70     struct timespec it_interval;  /* Timer interval */
  71     struct timespec it_value;     /* Initial expiration */
  72 };
  73 .fi
  74 .in
  75
  76 Each of the substructures of the
  77 .I itimerspec
  78 structure is a
  79 .I timespec
  80 structure that allows a time value to be specified
  81 in seconds and nanoseconds.
  82 These time values are measured according to the clock
  83 that was specified when the timer was created by
  84 .BR timer_create ()
  85
  86 If
  87 .I new_value->it_value
  88 specifies a non-zero value (i.e., either subfield is non-zero), then
  89 .BR timer_settime ()
  90 arms (starts) the timer,
  91 setting it to initially expire at the given time.
  92 (If the timer was already armed,
  93 then the previous settings are overwritten.)
  94 If
  95 .I new_value->it_value
  96 specifies a zero value
  97 (i.e., both subfields are zero),
  98 then the timer is disarmed.
  99
 100 The
 101 .I new_value->it_interval
 102 field specifies the period of the timer, in seconds and nanoseconds.
 103 If this field is non-zero, then each time that an armed timer expires,
 104 the timer is reloaded from the value specified in
 105 .IR new_value->it_interval .
 106 If
 107 .I new_value->it_interval
 108 specifies a zero value
 109 then the timer expires just once, at the time specified by
 110 .IR it_value .
 111
 112 By default, the initial expiration time specified in
 113 .I new_value->it_value
 114 is interpreted relative to the current time on the timer's
 115 clock at the time of the call.
 116 This can be modified by specifying
 117 .B TIMER_ABSTIME
 118 in
 119 .IR flags ,
 120 in which case
 121 .I new_value->it_value
 122 is interpreted as an absolute value as measured on the timer's clock;
 123 that is, the timer will expire when the clock value reaches the
 124 value specified by
 125 .IR new_value->it_value .
 126 If the specified absolute time has already passed,
 127 then the timer expires immediately,
 128 and the overrun count (see
 129 .BR timer_getoverrun (2))
 130 will be set correctly.
 131 .\" By experiment: the overrun count is set correctly, for CLOCK_REALTIME.
 132
 133 If the value of the
 134 .B CLOCK_REALTIME
 135 clock is adjusted while an absolute timer based on that clock is armed,
 136 then the expiration of the timer will be appropriately adjusted.
 137 Adjustments to the
 138 .B CLOCK_REALTIME
 139 clock have no effect on relative timers based on that clock.
 140 .\" Similar remarks might apply with respect to process and thread CPU time
 141 .\" clocks, but these clocks are not currently (2.6.28) settable on Linux.
 142
 143 If
 144 .I old_value
 145 is not NULL, then it returns the previous interval of the timer (in
 146 .IR old_value->it_interval )
 147 and the amount of time until the timer
 148 would previously have next expired (in
 149 .IR old_value->it_value ).
 150
 151 .BR timer_gettime ()
 152 returns the time until next expiration, and the the interval,
 153 for the timer specified by
 154 .IR timerid ,
 155 in the buffer pointed to by
 156 .IR curr_value .
 157 The time remaining until the next timer expiration is returned in
 158 .IR curr_value.it_value ;
 159 this is always a relative value, regardless of whether the
 160 .BR TIMER_ABSTIME
 161 flag was used when arming the timer.
 162 If the value returned in
 163 .IR curr_value.it_value
 164 is zero, then the timer is currently disarmed.
 165 The timer interval is returned in
 166 .IR curr_value.it_interval .
 167 If the value returned in
 168 .IR curr_value.it_interval
 169 is zero, then this is a "one-shot" timer.
 170 .SH RETURN VALUE
 171 On success,
 172 .BR timer_settime ()
 173 and
 174 .BR timer_gettime ()
 175 return 0.
 176 On error, \-1 is returned, and
 177 .I errno
 178 is set to indicate the error.
 179 .SH ERRORS
 180 These functions may fail with the following errors:
 181 .TP
 182 .B EFAULT
 183 .IR new_value ,
 184 .IR old_value ,
 185 or
 186 .I curr_value
 187 is not valid a pointer.
 188 .TP
 189 .B EINVAL
 190 .I timerid
 191 is invalid.
 192 .\" FIXME . eventually: invalid value in flags
 193 .PP
 194 .BR timer_settime ()
 195 may fail with the following errors:
 196 .TP
 197 .B EINVAL
 198 .I new_value.it_value
 199 is negative; or
 200 .I new_value.it_value.tv_nsec
 201 is negative or greater than 999,999,999.
 202 .SH VERSIONS
 203 These system calls are available since Linux 2.6.
 204 .SH CONFORMING TO
 205 POSIX.1-2001
 206 .SH EXAMPLE
 207 See
 208 .BR timer_create (2).
 209 .SH SEE ALSO
 210 .BR timer_create (2),
 211 .BR timer_settime (2),
 212 .BR timer_getoverrun (2),
 213 .BR time (7)