关于linux pthread 调度策略FIFO，抢占CPU的问题

Question

Hi 各位
最近在学习pthread时有点儿疑问，两个thread1和thread2调度策略均为FIFO，优先级分别为10和30，thread1先创建出来，无限循环打印thread1。 3秒后，创建thread2，无限循环打印thread2.
我理解当thread2执行时，thread1就完全被抢占了，只有thread2被不停打印出来。但是结果却是thread1和thread2都会打印出来。
代码如下，麻烦各位大神帮忙解释一下，谢谢了

 #include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
#include <sched.h>
pthread_t createSchedFifoThread(void* (*pThreadFunc)(void*), int priority)
{
        struct sched_param param;
        int policy;
        int ret;
        pthread_t id = 0;

        pthread_attr_t thread_attr;
        ret = pthread_attr_init(&thread_attr);
        if (0 != ret) {
                printf("Attribute creation failed");
                return id;
        }

        ret = pthread_attr_setschedpolicy(&thread_attr, SCHED_FIFO);
        if (0 != ret) {
                printf("pthread_attr_setschedpolicy failed");
                return id;
        }

        param.sched_priority = priority;

        ret = pthread_attr_setschedparam(&thread_attr, &param);
        if (0 != ret) {
                printf("Setting pthread_attr_setschedparam failed");
                return id;
        }

        ret = pthread_create(&id, &thread_attr, pThreadFunc, NULL);
        if (0 != ret) {
                printf("Thread creation failed");
                return id;
        }

        pthread_attr_destroy(&thread_attr);
        return id;
}

void* thread1(void *arg)
{
        while(1)
        {
                printf("thread1\n");
        }
}

void* thread2(void *arg)
{
        while(1)
        {
                printf("thread2\n");
        }
}

int main(void)
{
        pthread_t id;
        printf("create thread1\n");
        id = createSchedFifoThread(thread1, 10);
        sleep(3);
        printf("create thread2\n");
        id = createSchedFifoThread(thread2, 30);
        while(1)
        {
                sleep(1);
        }
        return 0;
}

Answer 1

这个只是优先级,决定你的程序是否先执行