（4）使用實(shí)例。

在前面已經(jīng)通過互斥鎖同步機(jī)制實(shí)現(xiàn)了多線程的順序執(zhí)行。下面的例子是用信號(hào)量同步機(jī)制實(shí)現(xiàn)3個(gè)線程之間的有序執(zhí)行，只是執(zhí)行順序是跟創(chuàng)建線程的順序相反。

/*thread_sem.c*/

#include stdio.h>

#include stdlib.h>

#include pthread.h>

#include semaphore.h>

#define THREAD_NUMBER 3 /* 線程數(shù) */

#define REPEAT_NUMBER 3 /* 每個(gè)線程中的小任務(wù)數(shù) */

#define DELAY_TIME_LEVELS 10.0 /*小任務(wù)之間的最大時(shí)間間隔*/

sem_t sem[THREAD_NUMBER];

void *thrd_func(void *arg)

{

int thrd_num = (int)arg;

int delay_time = 0;

int count = 0;

/* 進(jìn)行P操作 */

sem_wait(sem[thrd_num]);

printf(Thread %d is startingn, thrd_num);

for (count = 0; count  REPEAT_NUMBER; count++)

{

delay_time = (int)(rand() * DELAY_TIME_LEVELS/(RAND_MAX)) + 1;

sleep(delay_time);

printf(tThread %d: job %d delay = %dn,

thrd_num, count, delay_time);

}

printf(Thread %d finishedn, thrd_num);

pthread_exit(NULL);

}

int main(void)

{

pthread_t thread[THREAD_NUMBER];

int no = 0, res;

void * thrd_ret;

srand(time(NULL));

for (no = 0; no  THREAD_NUMBER; no++)

{

sem_init(sem[no], 0, 0);

res = pthread_create(thread[no], NULL, thrd_func, (void*)no);

if (res != 0)

{

printf(Create thread %d failedn, no);

exit(res);

}

}

printf(Create treads successn Waiting for threads to finish...n);

/* 對最后創(chuàng)建的線程的信號(hào)量進(jìn)行V操作 */

sem_post(sem[THREAD_NUMBER - 1]);

for (no = THREAD_NUMBER - 1; no >= 0; no--)

{

res = pthread_join(thread[no], thrd_ret);

if (!res)

{

printf(Thread %d joinedn, no);

}

else

{

printf(Thread %d join failedn, no);

}

/* 進(jìn)行V操作 */

sem_post(sem[(no + THREAD_NUMBER - 1) % THREAD_NUMBER]);

}

for (no = 0; no  THREAD_NUMBER; no++)

{

/* 刪除信號(hào)量 */

sem_destroy(sem[no]);

}

return 0;

}