Question

A thread which is joined to another can't continue its execution untill the thread to which it is joined has been completely executed or terminated.

遵循上面提到的线程特性，我在下面的代码中创建的最后一个线程也必须在过程Func()中打印它的语句，但事实并非如此。那是为什么？

其次，我无法为我在此程序中创建的任何线程设置priority。我错过了什么吗？

以下是代码：

void *Func(void *arg);
int main()
{
    pthread_t tid[5];

    pthread_attr_t *tattr;
    struct sched_param param;
    int pr,error,i;

    do
    {
        if( (tattr=(pthread_attr_t *)malloc(sizeof(pthread_attr_t)) )==NULL)
        {
            printf("Couldn't allocate memory for attribute object\n");
        }
    } while(tattr==NULL);

    if(error=pthread_attr_init(tattr))
    {
        printf(stderr,"Attribute initialization failed with error %s\n",strerror(error));
    }

    for(i=0;i<5;i++)
    {
        scanf("%d",&pr);

        param.sched_priority=pr;
        error=pthread_attr_setschedparam(tattr,&param);

        if(error!=0)
        {
            printf("failed to set priority\n");
        }

        if(i%2==0)
        {
            if(error=pthread_attr_setdetachstate(tattr,PTHREAD_CREATE_DETACHED))
            {
                fprintf(stderr,"Failed to set thread attributes with error %s\n",strerror(error));
            }
        }
        else if(error=pthread_attr_setdetachstate(tattr,PTHREAD_CREATE_JOINABLE))
        {
            fprintf(stderr,"Failed to set thread attributes with error %s\n",strerror(error));
        }

        pthread_create(&tid[i],tattr,Func,tattr);

        pthread_join(tid[i],NULL);
        printf("waiting for thread %d\n",i);
    }

    free(tattr);

    printf("All threads terminated\n");
    return 0;
}

void *Func(void *arg)
{
    pthread_attr_t *tattr=(pthread_attr_t *)arg;
    int state,error;

    struct sched_param param;

    error=pthread_attr_getdetachstate(tattr,&state);

    if(error==0 && state==PTHREAD_CREATE_DETACHED)
    {
        printf(" My state is DETACHED\n");
    }
    else if(error==0 && state==PTHREAD_CREATE_JOINABLE)
    {
        printf(" My state is JOINABLE\n");
    }

    error=pthread_attr_getschedpolicy(tattr,&param);

    if(error==0)
    {
        printf(" My Priority is %d\n",param.sched_priority);
    }

    return NULL;
}

Answer 1

您的操作系统是什么？

struct sched_param成员的含义是为调度策略SCHED_OTHER定义的实现。

例如，在GNU / Linux上，除非调度策略为SCHED_RR或SCHED_FIFO，否则sched_priority成员不会被使用，必须设置为0.

除此之外，第五个线程（最后一个）也打印其状态和优先级。

Posix主题C中的优先级

1 个答案: