1clock_nanosleep(2) System Calls Manual clock_nanosleep(2)
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6 clock_nanosleep - high-resolution sleep with specifiable clock
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9 Standard C library (libc, -lc), since glibc 2.17
10 Before glibc 2.17, Real-time library (librt, -lrt)
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14 #include <time.h>
15 int clock_nanosleep(clockid_t clockid, int flags,
17 const struct timespec *request,
18 struct timespec *_Nullable remain);
19 Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
21 clock_nanosleep():
23 _POSIX_C_SOURCE >= 200112L
24
26 Like nanosleep(2), clock_nanosleep() allows the calling thread to sleep
27 for an interval specified with nanosecond precision. It differs in al‐
28 lowing the caller to select the clock against which the sleep interval
29 is to be measured, and in allowing the sleep interval to be specified
30 as either an absolute or a relative value.
31 The time values passed to and returned by this call are specified using
33 timespec(3) structures.
34 The clockid argument specifies the clock against which the sleep inter‐
36 val is to be measured. This argument can have one of the following
37 values:
38 CLOCK_REALTIME
40 A settable system-wide real-time clock.
41 CLOCK_TAI (since Linux 3.10)
43 A system-wide clock derived from wall-clock time but ignoring
44 leap seconds.
45 CLOCK_MONOTONIC
47 A nonsettable, monotonically increasing clock that measures time
48 since some unspecified point in the past that does not change
49 after system startup.
50 CLOCK_BOOTTIME (since Linux 2.6.39)
52 Identical to CLOCK_MONOTONIC, except that it also includes any
53 time that the system is suspended.
54 CLOCK_PROCESS_CPUTIME_ID
56 A settable per-process clock that measures CPU time consumed by
57 all threads in the process.
58 See clock_getres(2) for further details on these clocks. In addition,
60 the CPU clock IDs returned by clock_getcpuclockid(3) and
61 pthread_getcpuclockid(3) can also be passed in clockid.
62 If flags is 0, then the value specified in request is interpreted as an
64 interval relative to the current value of the clock specified by
65 clockid.
66 If flags is TIMER_ABSTIME, then request is interpreted as an absolute
68 time as measured by the clock, clockid. If request is less than or
69 equal to the current value of the clock, then clock_nanosleep() returns
70 immediately without suspending the calling thread.
71 clock_nanosleep() suspends the execution of the calling thread until
73 either at least the time specified by request has elapsed, or a signal
74 is delivered that causes a signal handler to be called or that termi‐
75 nates the process.
76 If the call is interrupted by a signal handler, clock_nanosleep() fails
78 with the error EINTR. In addition, if remain is not NULL, and flags
79 was not TIMER_ABSTIME, it returns the remaining unslept time in remain.
80 This value can then be used to call clock_nanosleep() again and com‐
81 plete a (relative) sleep.
82
84 On successfully sleeping for the requested interval, clock_nanosleep()
85 returns 0. If the call is interrupted by a signal handler or encoun‐
86 ters an error, then it returns one of the positive error number listed
87 in ERRORS.
88
90 EFAULT request or remain specified an invalid address.
91 EINTR The sleep was interrupted by a signal handler; see signal(7).
93 EINVAL The value in the tv_nsec field was not in the range [0,
95 999999999] or tv_sec was negative.
96 EINVAL clockid was invalid. (CLOCK_THREAD_CPUTIME_ID is not a permit‐
98 ted value for clockid.)
99 ENOTSUP
101 The kernel does not support sleeping against this clockid.
102
104 POSIX.1-2008.
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107 POSIX.1-2001. Linux 2.6, glibc 2.1.
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110 If the interval specified in request is not an exact multiple of the
111 granularity underlying clock (see time(7)), then the interval will be
112 rounded up to the next multiple. Furthermore, after the sleep com‐
113 pletes, there may still be a delay before the CPU becomes free to once
114 again execute the calling thread.
115 Using an absolute timer is useful for preventing timer drift problems
117 of the type described in nanosleep(2). (Such problems are exacerbated
118 in programs that try to restart a relative sleep that is repeatedly in‐
119 terrupted by signals.) To perform a relative sleep that avoids these
120 problems, call clock_gettime(2) for the desired clock, add the desired
121 interval to the returned time value, and then call clock_nanosleep()
122 with the TIMER_ABSTIME flag.
123 clock_nanosleep() is never restarted after being interrupted by a sig‐
125 nal handler, regardless of the use of the sigaction(2) SA_RESTART flag.
126 The remain argument is unused, and unnecessary, when flags is TIMER_AB‐
128 STIME. (An absolute sleep can be restarted using the same request ar‐
129 gument.)
130 POSIX.1 specifies that clock_nanosleep() has no effect on signals dis‐
132 positions or the signal mask.
133 POSIX.1 specifies that after changing the value of the CLOCK_REALTIME
135 clock via clock_settime(2), the new clock value shall be used to deter‐
136 mine the time at which a thread blocked on an absolute
137 clock_nanosleep() will wake up; if the new clock value falls past the
138 end of the sleep interval, then the clock_nanosleep() call will return
139 immediately.
140 POSIX.1 specifies that changing the value of the CLOCK_REALTIME clock
142 via clock_settime(2) shall have no effect on a thread that is blocked
143 on a relative clock_nanosleep().
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146 clock_getres(2), nanosleep(2), restart_syscall(2), timer_create(2),
147 sleep(3), timespec(3), usleep(3), time(7)
148Linux man-pages 6.04 2023-03-30 clock_nanosleep(2)