1CLOCK_NANOSLEEP(2)         Linux Programmer's Manual        CLOCK_NANOSLEEP(2)
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NAME

6       clock_nanosleep - high-resolution sleep with specifiable clock
7

SYNOPSIS

9       #include <time.h>
10
11       int clock_nanosleep(clockid_t clock_id, int flags,
12                           const struct timespec *request,
13                           struct timespec *remain);
14
15       Link with -lrt (only for glibc versions before 2.17).
16
17   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
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19       clock_nanosleep():
20           _POSIX_C_SOURCE >= 200112L
21

DESCRIPTION

23       Like nanosleep(2), clock_nanosleep() allows the calling thread to sleep
24       for an interval specified with nanosecond  precision.   It  differs  in
25       allowing  the caller to select the clock against which the sleep inter‐
26       val is to be measured, and in allowing the sleep interval to be  speci‐
27       fied as either an absolute or a relative value.
28
29       The time values passed to and returned by this call are specified using
30       timespec structures, defined as follows:
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32           struct timespec {
33               time_t tv_sec;        /* seconds */
34               long   tv_nsec;       /* nanoseconds [0 .. 999999999] */
35           };
36
37       The clock_id argument specifies  the  clock  against  which  the  sleep
38       interval  is to be measured.  This argument can have one of the follow‐
39       ing values:
40
41       CLOCK_REALTIME   A settable system-wide real-time clock.
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43       CLOCK_MONOTONIC  A nonsettable,  monotonically  increasing  clock  that
44                        measures time since some unspecified point in the past
45                        that does not change after system startup.
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47       CLOCK_PROCESS_CPUTIME_ID
48                        A settable per-process clock that  measures  CPU  time
49                        consumed by all threads in the process.
50
51       See  clock_getres(2) for further details on these clocks.  In addition,
52       the   CPU   clock   IDs   returned   by   clock_getcpuclockid(3)    and
53       pthread_getcpuclockid(3) can also be passed in clock_id.
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55       If flags is 0, then the value specified in request is interpreted as an
56       interval relative to the  current  value  of  the  clock  specified  by
57       clock_id.
58
59       If  flags  is TIMER_ABSTIME, then request is interpreted as an absolute
60       time as measured by the clock, clock_id.  If request is  less  than  or
61       equal to the current value of the clock, then clock_nanosleep() returns
62       immediately without suspending the calling thread.
63
64       clock_nanosleep() suspends the execution of the  calling  thread  until
65       either  at least the time specified by request has elapsed, or a signal
66       is delivered that causes a signal handler to be called or  that  termi‐
67       nates the process.
68
69       If the call is interrupted by a signal handler, clock_nanosleep() fails
70       with the error EINTR.  In addition, if remain is not  NULL,  and  flags
71       was not TIMER_ABSTIME, it returns the remaining unslept time in remain.
72       This value can then be used to call clock_nanosleep()  again  and  com‐
73       plete a (relative) sleep.
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RETURN VALUE

76       On  successfully sleeping for the requested interval, clock_nanosleep()
77       returns 0.  If the call is interrupted by a signal handler  or  encoun‐
78       ters  an error, then it returns one of the positive error number listed
79       in ERRORS.
80

ERRORS

82       EFAULT request or remain specified an invalid address.
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84       EINTR  The sleep was interrupted by a signal handler; see signal(7).
85
86       EINVAL The value in the tv_nsec  field  was  not  in  the  range  0  to
87              999999999 or tv_sec was negative.
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89       EINVAL clock_id was invalid.  (CLOCK_THREAD_CPUTIME_ID is not a permit‐
90              ted value for clock_id.)
91

VERSIONS

93       The clock_nanosleep() system call first appeared in Linux 2.6.  Support
94       is available in glibc since version 2.1.
95

CONFORMING TO

97       POSIX.1-2001, POSIX.1-2008.
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NOTES

100       If  the  interval  specified in request is not an exact multiple of the
101       granularity underlying clock (see time(7)), then the interval  will  be
102       rounded  up  to  the  next multiple.  Furthermore, after the sleep com‐
103       pletes, there may still be a delay before the CPU becomes free to  once
104       again execute the calling thread.
105
106       Using  an  absolute timer is useful for preventing timer drift problems
107       of the type described in nanosleep(2).  (Such problems are  exacerbated
108       in  programs  that  try  to restart a relative sleep that is repeatedly
109       interrupted by signals.)  To perform a relative sleep that avoids these
110       problems,  call clock_gettime(2) for the desired clock, add the desired
111       interval to the returned time value, and  then  call  clock_nanosleep()
112       with the TIMER_ABSTIME flag.
113
114       clock_nanosleep()  is never restarted after being interrupted by a sig‐
115       nal handler, regardless of the use of the sigaction(2) SA_RESTART flag.
116
117       The  remain  argument  is  unused,  and  unnecessary,  when  flags   is
118       TIMER_ABSTIME.   (An  absolute  sleep  can  be restarted using the same
119       request argument.)
120
121       POSIX.1 specifies that clock_nanosleep() has no effect on signals  dis‐
122       positions or the signal mask.
123
124       POSIX.1  specifies  that after changing the value of the CLOCK_REALTIME
125       clock via clock_settime(2), the new clock value shall be used to deter‐
126       mine   the   time   at   which   a   thread   blocked  on  an  absolute
127       clock_nanosleep() will wake up; if the new clock value falls  past  the
128       end  of the sleep interval, then the clock_nanosleep() call will return
129       immediately.
130
131       POSIX.1 specifies that changing the value of the  CLOCK_REALTIME  clock
132       via  clock_settime(2)  shall have no effect on a thread that is blocked
133       on a relative clock_nanosleep().
134

SEE ALSO

136       clock_getres(2),  nanosleep(2),  restart_syscall(2),   timer_create(2),
137       sleep(3), usleep(3), time(7)
138

COLOPHON

140       This  page  is  part of release 5.02 of the Linux man-pages project.  A
141       description of the project, information about reporting bugs,  and  the
142       latest     version     of     this    page,    can    be    found    at
143       https://www.kernel.org/doc/man-pages/.
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147Linux                             2017-09-15                CLOCK_NANOSLEEP(2)
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