man2/clock_nanosleep.2

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  26 .TH CLOCK_NANOSLEEP 2 2017-09-15 "Linux" "Linux Programmer's Manual"
  27 .SH NAME
  28 clock_nanosleep \- high-resolution sleep with specifiable clock
  29 .SH SYNOPSIS
  30 .B #include <time.h>
  31 .nf
  32 .PP
  33 .BI "int clock_nanosleep(clockid_t " clock_id ", int " flags ,
  34 .BI "                    const struct timespec *" request ,
  35 .BI "                    struct timespec *" remain );
  36 .fi
  37 .PP
  38 Link with \fI\-lrt\fP (only for glibc versions before 2.17).
  39 .PP
  40 .ad l
  41 .in -4n
  42 Feature Test Macro Requirements for glibc (see
  43 .BR feature_test_macros (7)):
  44 .in
  45 .PP
  46 .BR clock_nanosleep ():
  47 .RS 4
  48 _POSIX_C_SOURCE\ >=\ 200112L
  49 .RE
  50 .ad
  51 .SH DESCRIPTION
  52 Like
  53 .BR nanosleep (2),
  54 .BR clock_nanosleep ()
  55 allows the calling thread to sleep for an interval specified
  56 with nanosecond precision.
  57 It differs in allowing the caller to select the clock against
  58 which the sleep interval is to be measured,
  59 and in allowing the sleep interval to be specified as
  60 either an absolute or a relative value.
  61 .PP
  62 The time values passed to and returned by this call are specified using
  63 .I timespec
  64 structures, defined as follows:
  65 .PP
  66 .in +4n
  67 .EX
  68 struct timespec {
  69     time_t tv_sec;        /* seconds */
  70     long   tv_nsec;       /* nanoseconds [0 .. 999999999] */
  71 };
  72 .EE
  73 .in
  74 .PP
  75 The
  76 .I clock_id
  77 argument specifies the clock against which the sleep interval
  78 is to be measured.
  79 This argument can have one of the following values:
  80 .TP 17
  81 .BR CLOCK_REALTIME
  82 A settable system-wide real-time clock.
  83 .TP
  84 .BR CLOCK_MONOTONIC
  85 A nonsettable, monotonically increasing clock that measures time
  86 since some unspecified point in the past that does not change after
  87 system startup.
  88 .\" On Linux this clock measures time since boot.
  89 .TP
  90 .BR CLOCK_PROCESS_CPUTIME_ID
  91 A settable per-process clock that measures CPU time consumed
  92 by all threads in the process.
  93 .\" There is some trickery between glibc and the kernel
  94 .\" to deal with the CLOCK_PROCESS_CPUTIME_ID case.
  95 .PP
  96 See
  97 .BR clock_getres (2)
  98 for further details on these clocks.
  99 In addition, the CPU clock IDs returned by
 100 .BR clock_getcpuclockid (3)
 101 and
 102 .BR pthread_getcpuclockid (3)
 103 can also be passed in
 104 .IR clock_id .
 105 .PP
 106 If
 107 .I flags
 108 is 0, then the value specified in
 109 .I request
 110 is interpreted as an interval relative to the current
 111 value of the clock specified by
 112 .IR clock_id .
 113 .PP
 114 If
 115 .I flags
 116 is
 117 .BR TIMER_ABSTIME ,
 118 then
 119 .I request
 120 is interpreted as an absolute time as measured by the clock,
 121 .IR clock_id .
 122 If
 123 .I request
 124 is less than or equal to the current value of the clock,
 125 then
 126 .BR clock_nanosleep ()
 127 returns immediately without suspending the calling thread.
 128 .PP
 129 .BR clock_nanosleep ()
 130 suspends the execution of the calling thread
 131 until either at least the time specified by
 132 .IR request
 133 has elapsed,
 134 or a signal is delivered that causes a signal handler to be called or
 135 that terminates the process.
 136 .PP
 137 If the call is interrupted by a signal handler,
 138 .BR clock_nanosleep ()
 139 fails with the error
 140 .BR EINTR .
 141 In addition, if
 142 .I remain
 143 is not NULL, and
 144 .I flags
 145 was not
 146 .BR TIMER_ABSTIME ,
 147 it returns the remaining unslept time in
 148 .IR remain .
 149 This value can then be used to call
 150 .BR clock_nanosleep ()
 151 again and complete a (relative) sleep.
 152 .SH RETURN VALUE
 153 On successfully sleeping for the requested interval,
 154 .BR clock_nanosleep ()
 155 returns 0.
 156 If the call is interrupted by a signal handler or encounters an error,
 157 then it returns one of the positive error number listed in ERRORS.
 158 .SH ERRORS
 159 .TP
 160 .B EFAULT
 161 .I request
 162 or
 163 .I remain
 164 specified an invalid address.
 165 .TP
 166 .B EINTR
 167 The sleep was interrupted by a signal handler; see
 168 .BR signal (7).
 169 .TP
 170 .B EINVAL
 171 The value in the
 172 .I tv_nsec
 173 field was not in the range 0 to 999999999 or
 174 .I tv_sec
 175 was negative.
 176 .TP
 177 .B EINVAL
 178 .I clock_id
 179 was invalid.
 180 .RB ( CLOCK_THREAD_CPUTIME_ID
 181 is not a permitted value for
 182 .IR clock_id .)
 183 .SH VERSIONS
 184 The
 185 .BR clock_nanosleep ()
 186 system call first appeared in Linux 2.6.
 187 Support is available in glibc since version 2.1.
 188 .SH CONFORMING TO
 189 POSIX.1-2001, POSIX.1-2008.
 190 .SH NOTES
 191 If the interval specified in
 192 .I request
 193 is not an exact multiple of the granularity underlying clock (see
 194 .BR time (7)),
 195 then the interval will be rounded up to the next multiple.
 196 Furthermore, after the sleep completes, there may still be a delay before
 197 the CPU becomes free to once again execute the calling thread.
 198 .PP
 199 Using an absolute timer is useful for preventing
 200 timer drift problems of the type described in
 201 .BR nanosleep (2).
 202 (Such problems are exacerbated in programs that try to restart
 203 a relative sleep that is repeatedly interrupted by signals.)
 204 To perform a relative sleep that avoids these problems, call
 205 .BR clock_gettime (2)
 206 for the desired clock,
 207 add the desired interval to the returned time value,
 208 and then call
 209 .BR clock_nanosleep ()
 210 with the
 211 .B TIMER_ABSTIME
 212 flag.
 213 .PP
 214 .BR clock_nanosleep ()
 215 is never restarted after being interrupted by a signal handler,
 216 regardless of the use of the
 217 .BR sigaction (2)
 218 .B SA_RESTART
 219 flag.
 220 .PP
 221 The
 222 .I remain
 223 argument is unused, and unnecessary, when
 224 .I flags
 225 is
 226 .BR TIMER_ABSTIME .
 227 (An absolute sleep can be restarted using the same
 228 .I request
 229 argument.)
 230 .PP
 231 POSIX.1 specifies that
 232 .BR clock_nanosleep ()
 233 has no effect on signals dispositions or the signal mask.
 234 .PP
 235 POSIX.1 specifies that after changing the value of the
 236 .B CLOCK_REALTIME
 237 clock via
 238 .BR clock_settime (2),
 239 the new clock value shall be used to determine the time
 240 at which a thread blocked on an absolute
 241 .BR clock_nanosleep ()
 242 will wake up;
 243 if the new clock value falls past the end of the sleep interval, then the
 244 .BR clock_nanosleep ()
 245 call will return immediately.
 246 .PP
 247 POSIX.1 specifies that
 248 changing the value of the
 249 .B CLOCK_REALTIME
 250 clock via
 251 .BR clock_settime (2)
 252 shall have no effect on a thread that is blocked on a relative
 253 .BR clock_nanosleep ().
 254 .SH SEE ALSO
 255 .BR clock_getres (2),
 256 .BR nanosleep (2),
 257 .BR restart_syscall (2),
 258 .BR timer_create (2),
 259 .BR sleep (3),
 260 .BR usleep (3),
 261 .BR time (7)