#include <semaphore.h>
int sem_timedwait(sem_t *sem, const struct timespec *abs_timeout);
Link with -pthread.
对于这个函数，主要在于abs_timeout这个参数。一开始我以为是传入需要等待的时间。像这样：
struct timespec ts;
ts.tv_nsec = ;
ts.tv_sec = ;
sem_timedwait(p_sem, &ts);
意思是我希望10秒1000纳秒才超时。结果，函数立即返回。网上查一下资料，才知道我错得多么离谱。这个abs_timeout竟然是UTC时间戳。看下面的代码http://linux.die.net/man/3/sem_timedwait：
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <semaphore.h>
#include <time.h>
#include <assert.h>
#include <errno.h>
#include <signal.h> sem_t sem; #define handle_error(msg) \
do { perror(msg); exit(EXIT_FAILURE); } while () static void
handler(int sig)
{
write(STDOUT_FILENO, "sem_post() from handler\n", );
if (sem_post(&sem) == -) {
write(STDERR_FILENO, "sem_post() failed\n", );
_exit(EXIT_FAILURE);
}
} int
main(int argc, char *argv[])
{
struct sigaction sa;
struct timespec ts;
int s; if (argc != ) {
fprintf(stderr, "Usage: %s <alarm-secs> <wait-secs>\n",
argv[]);
exit(EXIT_FAILURE);
} if (sem_init(&sem, , ) == -)
handle_error("sem_init"); /* Establish SIGALRM handler; set alarm timer using argv[1] */ sa.sa_handler = handler;
sigemptyset(&sa.sa_mask);
sa.sa_flags = ;
if (sigaction(SIGALRM, &sa, NULL) == -)
handle_error("sigaction"); alarm(atoi(argv[])); /* Calculate relative interval as current time plus
number of seconds given argv[2] */ if (clock_gettime(CLOCK_REALTIME, &ts) == -)
handle_error("clock_gettime"); ts.tv_sec += atoi(argv[]); printf("main() about to call sem_timedwait()\n");
while ((s = sem_timedwait(&sem, &ts)) == - && errno == EINTR)
continue; /* Restart if interrupted by handler */ /* Check what happened */ if (s == -) {
if (errno == ETIMEDOUT)
printf("sem_timedwait() timed out\n");
else
perror("sem_timedwait");
} else
printf("sem_timedwait() succeeded\n"); exit((s == ) ? EXIT_SUCCESS : EXIT_FAILURE);
}
在这段代码中，他没有处理溢出，下面是我的代码：
int32 CSeamphoreLock::time_lock( int32 nano_sec,int32 sec )
{
struct timespec ts; if ( clock_gettime( CLOCK_REALTIME,&ts ) < )
return -; ts.tv_sec += sec;
ts.tv_nsec += nano_sec; //#define NSECTOSEC 1000000000
ts.tv_sec += ts.tv_nsec/NSECTOSEC; //Nanoseconds [0 .. 999999999]
ts.tv_nsec = ts.tv_nsec%NSECTOSEC; return sem_timedwait( m_psem,&ts );
}
PS：居然用的时间戳，如果正在等待的时候管理员调整时间会不会让某个程序出问题呢？？为什么不用clock_gettime的CLOCK_MONOTONIC来判断呢。