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26 .TH CLOCK_NANOSLEEP 2 2015-08-08 "Linux" "Linux Programmer's Manual"
28 clock_nanosleep \- high-resolution sleep with specifiable clock
33 .BI "int clock_nanosleep(clockid_t " clock_id ", int " flags ,
34 .BI " const struct timespec *" request ,
35 .BI " struct timespec *" remain );
38 Link with \fI\-lrt\fP (only for glibc versions before 2.17).
42 Feature Test Macro Requirements for glibc (see
43 .BR feature_test_macros (7)):
46 .BR clock_nanosleep ():
48 _XOPEN_SOURCE\ >=\ 600 || _POSIX_C_SOURCE\ >=\ 200112L
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.
62 The time values passed to and returned by this call are specified using
64 structures, defined as follows:
69 time_t tv_sec; /* seconds */
70 long tv_nsec; /* nanoseconds [0 .. 999999999] */
77 argument specifies the clock against which the sleep interval
79 This argument can have one of the following values:
82 A settable system-wide real-time clock.
85 A nonsettable, monotonically increasing clock that measures time
86 since some unspecified point in the past that does not change after
88 .\" On Linux this clock measures time since boot.
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.
98 for further details on these clocks.
99 In addition, the CPU clock IDs returned by
100 .BR clock_getcpuclockid (3)
102 .BR pthread_getcpuclockid (3)
103 can also be passed in
108 is 0, then the value specified in
110 is interpreted as an interval relative to the current
111 value of the clock specified by
120 is interpreted as an absolute time as measured by the clock,
124 is less than or equal to the current value of the clock,
126 .BR clock_nanosleep ()
127 returns immediately without suspending the calling thread.
129 .BR clock_nanosleep ()
130 suspends the execution of the calling thread
131 until either at least the time specified by
134 or a signal is delivered that causes a signal handler to be called or
135 that terminates the process.
137 If the call is interrupted by a signal handler,
138 .BR clock_nanosleep ()
147 it returns the remaining unslept time in
149 This value can then be used to call
150 .BR clock_nanosleep ()
151 again and complete a (relative) sleep.
153 On successfully sleeping for the requested interval,
154 .BR clock_nanosleep ()
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.
164 specified an invalid address.
167 The sleep was interrupted by a signal handler.
172 field was not in the range 0 to 999999999 or
179 .RB ( CLOCK_THREAD_CPUTIME_ID
180 is not a permitted value for
184 .BR clock_nanosleep ()
185 system call first appeared in Linux 2.6.
186 Support is available in glibc since version 2.1.
188 POSIX.1-2001, POSIX.1-2008.
190 If the interval specified in
192 is not an exact multiple of the granularity underlying clock (see
194 then the interval will be rounded up to the next multiple.
195 Furthermore, after the sleep completes, there may still be a delay before
196 the CPU becomes free to once again execute the calling thread.
198 Using an absolute timer is useful for preventing
199 timer drift problems of the type described in
201 (Such problems are exacerbated in programs that try to restart
202 a relative sleep that is repeatedly interrupted by signals.)
203 To perform a relative sleep that avoids these problems, call
204 .BR clock_gettime (2)
205 for the desired clock,
206 add the desired interval to the returned time value,
208 .BR clock_nanosleep ()
213 .BR clock_nanosleep ()
214 is never restarted after being interrupted by a signal handler,
215 regardless of the use of the
222 argument is unused, and unnecessary, when
226 (An absolute sleep can be restarted using the same
230 POSIX.1 specifies that
231 .BR clock_nanosleep ()
232 has no effect on signals dispositions or the signal mask.
234 POSIX.1 specifies that after changing the value of the
237 .BR clock_settime (2),
238 the new clock value shall be used to determine the time
239 at which a thread blocked on an absolute
240 .BR clock_nanosleep ()
242 if the new clock value falls past the end of the sleep interval, then the
243 .BR clock_nanosleep ()
244 call will return immediately.
246 POSIX.1 specifies that
247 changing the value of the
250 .BR clock_settime (2)
251 shall have no effect on a thread that is blocked on a relative
252 .BR clock_nanosleep ().
254 .BR clock_getres (2),
256 .BR restart_syscall (2),
257 .BR timer_create (2),