int clock_nanosleep(clockid_t clockid, int flags,
const struct timespec *request,
struct timespec *remain);
Link with -lrt (only for glibc versions before 2.17).
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
clock_nanosleep():
_POSIX_C_SOURCE >= 200112L
The time values passed to and returned by this call are specified using timespec structures, defined as follows:
struct timespec {
time_t tv_sec; /* seconds */
long tv_nsec; /* nanoseconds [0 .. 999999999] */
};
The clockid argument specifies the clock against which the sleep interval is to be measured. This argument can have one of the following values:
See clock_getres(2) for further details on these clocks. In addition, the CPU clock IDs returned by clock_getcpuclockid(3) and pthread_getcpuclockid(3) can also be passed in clockid.
If flags is 0, then the value specified in request is interpreted as an interval relative to the current value of the clock specified by clockid.
If flags is TIMER_ABSTIME, then request is interpreted as an absolute time as measured by the clock, clockid. If request is less than or equal to the current value of the clock, then clock_nanosleep() returns immediately without suspending the calling thread.
clock_nanosleep() suspends the execution of the calling thread until either at least the time specified by request has elapsed, or a signal is delivered that causes a signal handler to be called or that terminates the process.
If the call is interrupted by a signal handler, clock_nanosleep() fails with the error EINTR. In addition, if remain is not NULL, and flags was not TIMER_ABSTIME, it returns the remaining unslept time in remain. This value can then be used to call clock_nanosleep() again and complete a (relative) sleep.
Using an absolute timer is useful for preventing timer drift problems of the type described in nanosleep(2). (Such problems are exacerbated in programs that try to restart a relative sleep that is repeatedly interrupted by signals.) To perform a relative sleep that avoids these problems, call clock_gettime(2) for the desired clock, add the desired interval to the returned time value, and then call clock_nanosleep() with the TIMER_ABSTIME flag.
clock_nanosleep() is never restarted after being interrupted by a signal handler, regardless of the use of the sigaction(2) SA_RESTART flag.
The remain argument is unused, and unnecessary, when flags is TIMER_ABSTIME. (An absolute sleep can be restarted using the same request argument.)
POSIX.1 specifies that clock_nanosleep() has no effect on signals dispositions or the signal mask.
POSIX.1 specifies that after changing the value of the CLOCK_REALTIME clock via clock_settime(2), the new clock value shall be used to determine the time at which a thread blocked on an absolute clock_nanosleep() will wake up; if the new clock value falls past the end of the sleep interval, then the clock_nanosleep() call will return immediately.
POSIX.1 specifies that changing the value of the CLOCK_REALTIME clock via clock_settime(2) shall have no effect on a thread that is blocked on a relative clock_nanosleep().