man2/timer_settime.2

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  23 .TH TIMER_SETTIME 2 2012-10-15 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 \fI\-lrt\fP.
  38 .sp
  39 .in -4n
  40 Feature Test Macro Requirements for glibc (see
  41 .BR feature_test_macros (7)):
  42 .in
  43 .sp
  44 .BR timer_settime (),
  45 .BR timer_gettime ():
  46 _POSIX_C_SOURCE\ >=\ 199309L
  47 .SH DESCRIPTION
  48 .BR timer_settime ()
  49 arms or disarms the timer identified by
  50 .IR timerid .
  51 The
  52 .I new_value
  53 argument is pointer to an
  54 .I itimerspec
  55 structure that specifies the new initial value and
  56 the new interval for the timer.
  57 The
  58 .I itimerspec
  59 structure is defined as follows:
  60
  61 .in +4n
  62 .nf
  63 struct timespec {
  64     time_t tv_sec;                /* Seconds */
  65     long   tv_nsec;               /* Nanoseconds */
  66 };
  67
  68 struct itimerspec {
  69     struct timespec it_interval;  /* Timer interval */
  70     struct timespec it_value;     /* Initial expiration */
  71 };
  72 .fi
  73 .in
  74
  75 Each of the substructures of the
  76 .I itimerspec
  77 structure is a
  78 .I timespec
  79 structure that allows a time value to be specified
  80 in seconds and nanoseconds.
  81 These time values are measured according to the clock
  82 that was specified when the timer was created by
  83 .BR timer_create (2)
  84
  85 If
  86 .I new_value->it_value
  87 specifies a nonzero value (i.e., either subfield is nonzero), then
  88 .BR timer_settime ()
  89 arms (starts) the timer,
  90 setting it to initially expire at the given time.
  91 (If the timer was already armed,
  92 then the previous settings are overwritten.)
  93 If
  94 .I new_value->it_value
  95 specifies a zero value
  96 (i.e., both subfields are zero),
  97 then the timer is disarmed.
  98
  99 The
 100 .I new_value->it_interval
 101 field specifies the period of the timer, in seconds and nanoseconds.
 102 If this field is nonzero, then each time that an armed timer expires,
 103 the timer is reloaded from the value specified in
 104 .IR new_value->it_interval .
 105 If
 106 .I new_value->it_interval
 107 specifies a zero value
 108 then the timer expires just once, at the time specified by
 109 .IR it_value .
 110
 111 By default, the initial expiration time specified in
 112 .I new_value->it_value
 113 is interpreted relative to the current time on the timer's
 114 clock at the time of the call.
 115 This can be modified by specifying
 116 .B TIMER_ABSTIME
 117 in
 118 .IR flags ,
 119 in which case
 120 .I new_value->it_value
 121 is interpreted as an absolute value as measured on the timer's clock;
 122 that is, the timer will expire when the clock value reaches the
 123 value specified by
 124 .IR new_value->it_value .
 125 If the specified absolute time has already passed,
 126 then the timer expires immediately,
 127 and the overrun count (see
 128 .BR timer_getoverrun (2))
 129 will be set correctly.
 130 .\" By experiment: the overrun count is set correctly, for CLOCK_REALTIME.
 131
 132 If the value of the
 133 .B CLOCK_REALTIME
 134 clock is adjusted while an absolute timer based on that clock is armed,
 135 then the expiration of the timer will be appropriately adjusted.
 136 Adjustments to the
 137 .B CLOCK_REALTIME
 138 clock have no effect on relative timers based on that clock.
 139 .\" Similar remarks might apply with respect to process and thread CPU time
 140 .\" clocks, but these clocks are not currently (2.6.28) settable on Linux.
 141
 142 If
 143 .I old_value
 144 is not NULL, then it points to a buffer
 145 that is used to return 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 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 a valid 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_getoverrun (2),
 212 .BR time (7)