Linux sem_trywait实现sem_timedwait
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- sem_timedwait说明
int sem_timedwait(sem_t *sem, const struct timespec *abs_timeout);
其中第2个参数 struct timespec *abs_timeout要求为绝对时间,如果手动将系统时间往后修改会导致sem_timedwait长时间阻塞
- sem_trywait说明
int sem_trywait(sem_t *sem);
sem_trywait与 sem_wait() 类似,若信号不可用,则返回错误(errno 设置为EAGAIN)而不是阻塞
- sem_timedwait自定义实现
#include <stdio.h>
#include <pthread.h>
#include <unistd.h>
#include <sys/time.h>
#include <sys/types.h>
#include <semaphore.h>
#include <errno.h>
unsigned long long GetClockTimeMS( void )
{
unsigned long long time;
struct timespec curTime;
clock_gettime(CLOCK_MONOTONIC_RAW, &curTime);
time = curTime.tv_sec;
time *= 1000;
time += curTime.tv_nsec/1000000;
return time;
}
unsigned long long GetClockTimeUS( void )
{
unsigned long long time;
struct timespec curTime;
clock_gettime(CLOCK_MONOTONIC_RAW, &curTime);
time = curTime.tv_sec;
time *= 1000000;
time += curTime.tv_nsec/1000;
return time;
}
unsigned long long GetClockTimeNS(void)
{
unsigned long long time;
struct timespec curTime;
clock_gettime(CLOCK_MONOTONIC_RAW, &curTime);
time = curTime.tv_sec;
time *= 1000000000;
time += curTime.tv_nsec;
return time;
}
int SleepEx(int us)
{
struct timeval timeout;
timeout.tv_sec = us/1000000;
timeout.tv_usec = us%1000000;
if(-1 == select(0, NULL, NULL, NULL, &timeout))
{
return errno;
}
return 0;
}
int WaitEvent(sem_t *hEvent, unsigned int milliseconds)
{
int ret;
#if 0
struct timespec timeout = { 0 };
#ifdef _DEBUG
ret = clock_gettime(CLOCK_REALTIME, &timeout);
#else
clock_gettime(CLOCK_REALTIME, &timeout);
#endif//_DEBUG
timeout.tv_sec += (milliseconds / 1000);
timeout.tv_nsec += ((milliseconds % 1000) * 1000000);
if (0 == sem_timedwait((sem_t *)hEvent, &timeout))
{
return 0;
}
return errno;
#else
unsigned long long timeout = milliseconds*1000;//微秒
unsigned long long beg = GetClockTimeUS();
unsigned long long cur;
do
{
if (0 == sem_trywait((sem_t *)hEvent))
{
return 0;
}
ret = errno;
if (EAGAIN != ret)
{
return ret;
}
cur = GetClockTimeUS();
if (cur - beg >= timeout)
{
break;
}
SleepEx(1);
} while (1);
return ETIMEDOUT;
#endif
}
int main(void)
{
sem_t event;
sem_init(&event, 0, 0);
unsigned long long begUS = GetClockTimeUS();
WaitEvent(&event, 2000);
printf("end %llu..\n", GetClockTimeUS() - begUS);
return 0;
}
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