问Linux semaphore.h挂起/等待队列策略

EN

#include <string.h>
#include <pthread.h>
#include <semaphore.h>
#include "stdlib.h"
#include "stdio.h"

sem_t b_sem;

int test_routine(int my_num)
{
    usleep(1+ my_num * 1000);
    printf("I'm %d, going to wait sem\n", my_num);
    sem_wait(&b_sem);
    printf("I'm %d, I got the sem\n", my_num);
    while(1)
    {
            sleep(1);
    }
}

int main()
{
    int i;
    int pthrid[4] = {0,0,0,0};
    pthread_attr_t attr[4];
    struct sched_param prv_priority[4];

    struct sched_param param;
    param.sched_priority = sched_get_priority_max(SCHED_FIFO);
    sched_setscheduler(0, SCHED_FIFO, &param);

    sem_init(&b_sem, 1, 0);

    for( i = 0 ; i < 4 ; i++ )
    {
            pthread_attr_init(&attr[i]);
            pthread_attr_getschedparam(&attr[i], &prv_priority[i]);
            pthread_attr_setschedpolicy(&attr[i], SCHED_FIFO);
            prv_priority[i].sched_priority = (10 + i*10);
            printf("test start, thread %d has priority %d\n", i ,prv_priority[i].sched_priority);
            pthread_attr_setschedparam(&attr[i], &prv_priority[i]);
            pthread_create(&pthrid[i], &attr[i], test_routine, i);
    }

    sleep(1);

    for( i = 0 ; i < 4 ; i++ )
    {
            printf("give sem\n");
            sem_post(&b_sem);
            sleep(1);
    }

    sleep(100000);

}

test start, thread 0 has priority 10
test start, thread 1 has priority 20
test start, thread 2 has priority 30
test start, thread 3 has priority 40
I'm 0, going to wait sem
I'm 1, going to wait sem
I'm 2, going to wait sem
I'm 3, going to wait sem
give sem
I'm 0, I got the sem
give sem
I'm 1, I got the sem
give sem
I'm 2, I got the sem
give sem
I'm 3, I got the sem