在评论在pthread_join该线程同一个线程子程序的多个执行 [英] Multiple execution of same thread subroutine on commenting pthread_join for that thread

问题描述

我是新来穿线。
在这里，如果我评论在pthread_join（线程1，NULL），那么在输出有时我得到

 线程2
    线程1
    线程1
 

我不能够理解为什么线程1轨迹来两次，是什么在pthread_join的确切功能。

另外，请参考上线程的概念对于初学者一些教程。

 无效* print_message_function（无效* PTR）;
    主要（）
    {
            的pthread_t线程1，线程;
            字符* MESSAGE1 =线程1;
            字符* MESSAGE2 =线程2;
            INT iret1，iret2;
            iret1 =在pthread_create（安培;线程1，NULL，print_message_function，（无效*）MESSAGE1）;
            iret2 =在pthread_create（安培;线程2，NULL，print_message_function，（无效*）消息2）;
            在pthread_join（线程1，NULL）;            在pthread_join（线程2，NULL）;            的printf（线程1返回数：％d \\ n，iret1）;
            的printf（线程2返回数：％d \\ n，iret2）;
            出口（0）;
    }    无效* print_message_function（无效* PTR）
    {
            字符*消息;
            消息=（字符*）PTR;
            的printf（％S \\ n，邮件）;
    }
 

解决方案

如果我得到这些结果，首先我要做到以下几点：

1）代替下面的线条，

  iret1 =在pthread_create（安培;线程1，NULL，print_message_function，（无效*）MESSAGE1）;iret2 =在pthread_create（安培;线程2，NULL，print_message_function，（无效*）消息2）;
在pthread_join（线程1，NULL）;在pthread_join（线程2，NULL）;
 

其替换，

  iret1 =在pthread_create（安培;线程1，NULL，print_message_function，（无效*）MESSAGE1）;在pthread_join（线程1，NULL）;
iret2 =在pthread_create（安培;线程2，NULL，print_message_function，（无效*）消息2）;在pthread_join（线程2，NULL）;
 

和看到的结果是什么。

2）内的线程函数，你需要调用了pthread_exit（退出）;这是从线程功能来退出有道。在函数结尾做到这一点。

 无效* print_message_function（无效* PTR）
{
        字符*消息;
        消息=（字符*）PTR;
        的printf（％S \\ n，邮件）;
        了pthread_exit（退出）;
    }
 

如果你用这种方法做它，最好你应该不会遇到任何问题。在任何情况下，我假设你正在使用 -D_REENTRANT的gcc -o threadex threadex.c -lpthread

编译程序

这是不是最终的解决方案。如果进展顺利的话，我们可以继续在同一时间同时启动线程的下一个步骤。

请将这些更改后分享反馈。

I am new to threading. Here if I comment pthread_join( thread1, NULL) then in the output sometimes I get

    Thread2
    Thread1
    Thread1

I am not able to understand why Thread1 trace is coming twice and what is the exact functionality of pthread_join.

Also, please refer some tutorial on threading concepts for beginners.

    void *print_message_function( void *ptr );
    main()
    {
            pthread_t thread1, thread2;
            char *message1 = "Thread 1";
            char *message2 = "Thread 2";
            int  iret1, iret2;
            iret1 = pthread_create( &thread1, NULL, print_message_function, (void*) message1);
            iret2 = pthread_create( &thread2, NULL, print_message_function, (void*) message2);
            pthread_join( thread1, NULL);

            pthread_join( thread2, NULL); 

            printf("Thread 1 returns: %d\n",iret1);
            printf("Thread 2 returns: %d\n",iret2);
            exit(0);
    }

    void *print_message_function( void *ptr )
    {
            char *message;
            message = (char *) ptr;
            printf("%s \n", message);
    }

解决方案

If I am getting these results, first of all I would do the following:

1) Instead of below lines,

iret1 = pthread_create( &thread1, NULL, print_message_function, (void*) message1);

iret2 = pthread_create( &thread2, NULL, print_message_function, (void*) message2);
pthread_join( thread1, NULL);

pthread_join( thread2, NULL); 

replace it with,

iret1 = pthread_create( &thread1, NULL, print_message_function, (void*) message1);

pthread_join( thread1, NULL);
iret2 = pthread_create( &thread2, NULL, print_message_function, (void*) message2);

pthread_join( thread2, NULL); 

and see what is the result.

2) Inside your thread function, you need to call pthread_exit("Exit"); This is a proper way to exit from the thread function. Do it at the end of function.

void *print_message_function( void *ptr )
{
        char *message;
        message = (char *) ptr;
        printf("%s \n", message);
        pthread_exit("Exit"); 
    }

If you are doing it this way, ideally you should not face any problem. In every case, i am assuming you are compiling your program using gcc -D_REENTRANT -o threadex threadex.c -lpthread

This is not the final solution. If it is going well, then we can proceed to next step of starting both the threads at a time.

Please share the feedback after incorporating these changes.

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