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linux线程调度和优先级设置有关问题（求解释） [复制链接]

dolinuxbest

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发表于 2011-07-11 16:30 |只看该作者 |倒序浏览
linux可以设置线程的调度和优先级。支持三种调度方法。
1.SCHED_OTHER
分时调度策略，线程优先级为0；
2.SCHED_FIFO
实时调度策略，先到先服务。一当占用CPU，除非自己阻塞或结束或有更高优先级线程，否则会一直运行，线程优先级为1－99；
3.SCHED_RR
实时调度策略，时间片轮转 。其不会一直占用CPU，运行一个时间片后会让出CPU给自己同优先级的线程；

我编了一点程序，创建两个线程，都是SCHED_FIFO，线程1优先级为1，线程2为99。按理说，线程2会抢占线程1.线程2运行结束后线程1才运行。但是运行的结果却是两个线程交替执行。求大牛解释！
代码如下


/*
* main.c
*
*  Created on: 2011-7-4
*      Author: lis
*/

#include<stdio.h>
#include<stdlib.h>
#include<pthread.h>
#include<sched.h>
#include<unistd.h>
#include<sys/time.h>
#include<sys/resource.h>
#include<string.h>

void FunThread1()
{
        printf("thread 1 start\n");

        int i,j;
        int policy;
        int priority;
        struct sched_param param;

        pthread_getschedparam(pthread_self(),&policy,&param);
        if(policy==SCHED_OTHER)
        {
         printf("thread 1 SCHED_OTHER\n");
         priority = param.sched_priority;
                printf("thread 1 SCHED_OTHER=%d \n",priority);
        }
        if(policy==SCHED_RR)
        {
         printf("thread 1 SCHED_RR\n");
         priority = param.sched_priority;
        printf("thread 1 SCHED_RR=%d \n",priority);
        }
        if(policy==SCHED_FIFO)
        {
                printf("thread 1 SCHED_FIFO\n");
                priority = param.sched_priority;
                printf("thread 1 SCHED_FIFO=%d \n",priority);
        }

        for(i=1;i<20;i++)
        {
        for(j=1;j<10000000;j++)
        {
        }
        printf("this is thread 1\n");
        }
        printf("Thread 1 exit\n");
}



void FunThread2()
{

        printf("thread 2 start\n");

        int i,j;
        int policy;
        int priority;
        struct sched_param param;

        pthread_getschedparam(pthread_self(),&policy,&param);
        if(policy==SCHED_OTHER)
        {
         printf("thread 2 SCHED_OTHER\n");
         priority = param.sched_priority;
                printf("thread 2 SCHED_OTHER=%d \n",priority);
        }
        if(policy==SCHED_RR)
        {
         printf("thread 2 SCHED_RR\n");
         priority = param.sched_priority;
        printf("thread 2 SCHED_RR=%d \n",priority);
        }
        if(policy==SCHED_FIFO)
        {
                printf("thread 2 SCHED_FIFO\n");
                priority = param.sched_priority;
                printf("thread 2 SCHED_FIFO=%d \n",priority);
        }

        for(i=1;i<20;i++)
        {
        for(j=1;j<10000000;j++)
        {
        }
        printf("this is thread 2\n");
        }
        printf("Thread 2 exit\n");
}

int main(int argc, char *argv[])
{

        int i;
        i=getuid();
        if(i==0)
        printf("The current user is root\n");
        else
        printf("The current user is not root\n");

        pthread_t tid1,tid2;
        pthread_attr_t attr1,attr2;
        struct sched_param param1;
        param1.sched_priority=1;
        struct sched_param param2;
        param2.sched_priority=99;

        pthread_attr_init(&attr1);
        pthread_attr_init(&attr2);

        pthread_attr_setinheritsched(&attr1,PTHREAD_EXPLICIT_SCHED);
        pthread_attr_setinheritsched(&attr2,PTHREAD_EXPLICIT_SCHED);

        pthread_attr_setschedpolicy(&attr1,SCHED_FIFO);
        pthread_attr_setschedparam(&attr1,&param1);
        pthread_attr_setschedpolicy(&attr2,SCHED_FIFO);
        pthread_attr_setschedparam(&attr2,&param2);


        sleep(1);
        pthread_create(&tid1,&attr1,(void *)FunThread1,NULL);

        pthread_create(&tid2,&attr2,(void *)FunThread2,NULL);

        pthread_join(tid1,NULL);
        pthread_join(tid2,NULL);

        pthread_attr_destroy(&attr1);
        pthread_attr_destroy(&attr2);

        return 0;
}

运行结果：
The current user is root
thread 1 start
thread 2 start
thread 1 SCHED_FIFO
thread 2 SCHED_FIFO
thread 1 SCHED_FIFO=1
thread 2 SCHED_FIFO=99
this is thread 1
this is thread 2
this is thread 1
this is thread 2
this is thread 1
this is thread 2
this is thread 1
this is thread 2
this is thread 1
this is thread 2
this is thread 1
this is thread 2
this is thread 1
this is thread 2
this is thread 1
this is thread 2
this is thread 1
this is thread 2
this is thread 1
this is thread 2
this is thread 1
this is thread 2
this is thread 1
this is thread 2
this is thread 1
this is thread 2
this is thread 1
this is thread 2
this is thread 1
this is thread 2
this is thread 1
this is thread 2
this is thread 1
this is thread 2
this is thread 1
this is thread 2
this is thread 1
Thread 1 exit
this is thread 2
Thread 2 exit
linux线程调度, linux线程调度
hanzhenlll

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射手座 日期:2014-08-04 16:49:43
2楼 [报告]
发表于 2011-07-12 17:13 |只看该作者
因为有时间片。。。。  所以会切换，而且必须切换。。。。

假如真如你想的，我写个WHILE 1 或者 死锁 那么你电脑肯定理所应当的死机了， 你觉得合理吗？
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qprevf

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3楼 [报告]
发表于 2011-07-12 22:34 |只看该作者
优先级是会动态改变的，不是你设多高，他就不会变
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dolinuxbest

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4楼 [报告]
发表于 2011-07-13 10:17 |只看该作者
回复 2# hanzhenlll


    那如何体现线程2的优先级比线程1高？
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dolinuxbest

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5楼 [报告]
发表于 2011-07-13 10:22 |只看该作者
回复 3# qprevf


    如果会改变，改变的原则是什么？
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chen0610

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6楼 [报告]
发表于 2012-08-17 15:11 |只看该作者
本帖最后由 chen0610 于 2012-08-17 15:13 编辑

体现线程2的优先级比线程1高最好是用条件变量，线程2和线程1同时等待一个条件变量，另外再创建一个线程3释放条件变量。
哪一个线程先获得条件变量就说明哪一个的线程的优先级高。
在你的代码上修改的：
#include<stdio.h>
#include<stdlib.h>
#include<pthread.h>
#include<sched.h>
#include<unistd.h>
#include<sys/time.h>
#include<sys/resource.h>
#include<string.h>

pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
pthread_cond_t cond = PTHREAD_COND_INITIALIZER;

void *FunThread1(void *arg)
{
    int i;
    int policy;
    int priority;
    struct sched_param param;

        printf("Thread 1 start\n");

    pthread_getschedparam(pthread_self(),&policy,&param);
    if(policy==SCHED_OTHER)
    {
                printf("thread 1 SCHED_OTHER\n");
                priority = param.sched_priority;
                printf("thread 1 SCHED_OTHER=%d \n",priority);
    }
    if(policy==SCHED_RR)
    {
                printf("thread 1 SCHED_RR\n");
                priority = param.sched_priority;
                printf("thread 1 SCHED_RR=%d \n",priority);
    }
    if(policy==SCHED_FIFO)
    {
                printf("thread 1 SCHED_FIFO\n");
                priority = param.sched_priority;
                printf("thread 1 SCHED_FIFO=%d \n",priority);
    }

    for(i=11;i<=20;i++)
    {
                pthread_mutex_lock(&mutex);
        pthread_cond_wait(&cond,&mutex);
        printf("thread 1: i = %d.\n", i);
        pthread_mutex_unlock(&mutex);
    }
    printf("Thread 1 exit\n");
}



void *FunThread2(void *arg)
{
        int j;
        int policy;
        int priority;
        struct sched_param param;

        printf("Thread 2 start\n");

        pthread_getschedparam(pthread_self(),&policy,&param);
        if(policy==SCHED_OTHER)
        {
                printf("thread 2 SCHED_OTHER\n");
                priority = param.sched_priority;
                printf("thread 2 SCHED_OTHER=%d \n",priority);
        }
        if(policy==SCHED_RR)
        {
                printf("thread 2 SCHED_RR\n");
                priority = param.sched_priority;
                printf("thread 2 SCHED_RR=%d \n",priority);
        }
        if(policy==SCHED_FIFO)
        {
                printf("thread 2 SCHED_FIFO\n");
                priority = param.sched_priority;
                printf("thread 2 SCHED_FIFO=%d \n",priority);
        }

        for(j=1;j<=10;j++)
        {
                pthread_mutex_lock(&mutex);
        pthread_cond_wait(&cond,&mutex);
        printf("thread 2: j = %d.\n", j);
        pthread_mutex_unlock(&mutex);
        }
        printf("Thread 2 exit\n");
}

void *FunThread3(void *arg)
{
        int j;
        int policy;
        int priority;
        struct sched_param param;

        printf("Thread 3 start\n");

        pthread_getschedparam(pthread_self(),&policy,&param);
        if(policy==SCHED_OTHER)
        {
                printf("thread 3 SCHED_OTHER\n");
                priority = param.sched_priority;
                printf("thread 3 SCHED_OTHER=%d \n",priority);
        }
        if(policy==SCHED_RR)
        {
                printf("thread 3 SCHED_RR\n");
                priority = param.sched_priority;
                printf("thread 3 SCHED_RR=%d \n",priority);
        }
        if(policy==SCHED_FIFO)
        {
                printf("thread 3 SCHED_FIFO\n");
                priority = param.sched_priority;
                printf("thread 3 SCHED_FIFO=%d \n",priority);
        }

        for(;;)
        {
                pthread_mutex_lock(&mutex);
        pthread_cond_signal(&cond);
        pthread_mutex_unlock(&mutex);
        sleep(3);
        }
        printf("Thread 3 exit\n");
}


int main(int argc, char *argv[])
{
        int i;
        pthread_t tid1,tid2,tid3;
        pthread_attr_t attr1,attr2,attr3;
        struct sched_param param1, param2, param3;
       
        i=getuid();
        if(i==0)
        {
                printf("The current user is root\n");
        }
        else
        {
                printf("The current user is not root\n");
        }

        param1.sched_priority=20;
        param2.sched_priority=30;
        param3.sched_priority=10;

        pthread_attr_init(&attr1);
        pthread_attr_init(&attr2);
        pthread_attr_init(&attr3);

        pthread_attr_setinheritsched(&attr1,PTHREAD_EXPLICIT_SCHED);
        pthread_attr_setinheritsched(&attr2,PTHREAD_EXPLICIT_SCHED);
        pthread_attr_setinheritsched(&attr3,PTHREAD_EXPLICIT_SCHED);

        pthread_attr_setschedpolicy(&attr1,SCHED_FIFO);
        pthread_attr_setschedparam(&attr1,&param1);
       
        pthread_attr_setschedpolicy(&attr2,SCHED_FIFO);
        pthread_attr_setschedparam(&attr2,&param2);
       
        pthread_attr_setschedpolicy(&attr3,SCHED_FIFO);
        pthread_attr_setschedparam(&attr3,&param3);

        sleep(1);

        pthread_create(&tid1,&attr1,FunThread1,NULL);

        sleep(1);

        pthread_create(&tid2,&attr2,FunThread2,NULL);

        sleep(1);

        pthread_create(&tid3,&attr3,FunThread3,NULL);

        pthread_join(tid3,NULL);

        pthread_attr_destroy(&attr1);
        pthread_attr_destroy(&attr2);

    return 0;
}

结果如下：
[root@localhost test]# gcc -o test test.c -lpthread
[root@localhost test]# ./test
The current user is root
Thread 1 start
thread 1 SCHED_FIFO
thread 1 SCHED_FIFO=20
Thread 2 start
thread 2 SCHED_FIFO
thread 2 SCHED_FIFO=30
Thread 3 start
thread 3 SCHED_FIFO
thread 3 SCHED_FIFO=10
thread 2: j = 1.
thread 2: j = 2.
thread 2: j = 3.
thread 2: j = 4.
thread 2: j = 5.
thread 2: j = 6.
thread 2: j = 7.
thread 2: j = 8.
thread 2: j = 9.
thread 2: j = 10.
Thread 2 exit
thread 1: i = 11.
thread 1: i = 12.
thread 1: i = 13.
thread 1: i = 14.
thread 1: i = 15.
thread 1: i = 16.
thread 1: i = 17.
thread 1: i = 18.
thread 1: i = 19.
thread 1: i = 20.
Thread 1 exit
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