内容简介
#define _POSIX_C_SOURCE 199309%uA0#include <time.h>int nanosleep(const struct timespec *req, struct timespec *rem)
DESCRIPTION
nanosleep() delays the execution of the program for at least the time specified in%uA0*req. The function can return earlier if a signal has been delivered to the process. In this case, it returns -1, sets%uA0errno%uA0to%uA0EINTR, and writes the remaining time into the structure pointed to by%uA0rem%uA0unless%uA0rem%uA0is NULL. The value of%uA0*remꃊn then be used to callnanosleep() again and complete the specified pause.The structure%uA0timespec%uA0is used to specify intervals of time with nanosecond precision. It is specified in%uA0<time.h>%uA0and has the form
struct timespec {
time_t tv_sec /* seconds */
long tv_nsec /* nanoseconds */
}
|
The value of the nanoseconds field must be in the range 0 to 999999999.
Compared to%uA0sleep(3) and%uA0usleep(3),%uA0nanosleep() has the advantage of not affecting any signals, it is standardized by POSIX, it provides higher timing resolution, and it allows to continue a sleep that has been interrupted by a signal more easily.
返回值
On successfully sleeping for the requested interval,%uA0nanosleep() returns 0. If the call is interrupted by a signal handler or encounters an error, then it returns -1, with%uA0errno%uA0set to indicate the error.错误
| 标签 | 描述 |
|---|---|
| EFAULT | 问题从用户空间复制信息。 |
| EINTR | The pause has been interrupted by a non-blocked signal that was delivered to the process. The remaining sleep time has been written into *rem%uA0so that the process can easily callnanosleep() again and continue with the pause. |
| EINVAL | The value in the%uA0tv_nsec%uA0field was not in the range 0 to 999999999 or%uA0tv_sec%uA0was negative. |
BUGS
The current implementation of%uA0nanosleep() is based on the normal kernel timer mechanism, which has a resolution of 1/HZ%uA0s (see%uA0time(7)). Therefore,%uA0nanosleep() pauses always for at least the specified time, however it can take up to 10 ms longer than specified until the process becomes runnable again. For the same reason, the value returned in case of a delivered signal in *rem%uA0is usually rounded to the next larger multiple of 1/HZ%uA0s.Old behaviour
In order to support applications requiring much more precise pauses (e.g., in order to control some time-critical hardware),%uA0nanosleep() would handle pauses of up to 2 ms by busy waiting with microsecond precision when called from a process scheduled under a real-time policy like%uA0SCHED_FIFO%uA0or%uA0SCHED_RR. This special extension was removed in kernel 2.5.39, hence is still present in current 2.4 kernels, but not in 2.6 kernels.In Linux 2.4, if%uA0nanosleep() is stopped by a signal (e.g., SIGTSTP), then the call fails with the error%uA0EINTRꂯter the process is resumed by a SIGCONT signal. If the system call is subsequently restarted, then the time that the process spent in the stopped state isnot%uA0counted against the sleep interval.