终止线程后返回值错误

Question

我接近在C并行线程和我开始写作非常愚蠢的程序,让他们的窍门.我试图创建一个包含两个线程的程序,他们应该打印他们的名字,并在终止执行时收集他们的状态.所以我的代码是:

//Function declaration
void *state_your_name(char*);

//Function definition

//Passing a string as parameter for 
//outputting the name of the thread
void *state_your_name(char *name) {
    //Declaration of the variable containing the return status
    void* status;

    //Printing out the string
    printf("%s\n", name);
    //Exiting the thread and saving the return value
    pthread_exit(status);
}

int main(void) {
    pthread_t tid_1, tid_2;
    void * status;

    //Creating thread 1...
    if (pthread_create(&tid_1, NULL, state_your_name, "Thread 1")) {
        printf("Error creating thread 1");
        exit(1);
    }

    //Creating thread 2...    
    if (pthread_create(&tid_2, NULL, state_your_name, "Thread 2")) {
        printf("Error creating thread 2");
        exit(1);
    }

    //Waiting for thread 1 to terminate and 
    //collecting the return value...    
    if (pthread_join(tid_1, (void *) &status)) {
        printf("Error joining thread 1");
        exit(1);
    }
        printf("Thread 1 - Return value: %d\n", (int)status );

    //Waiting for thread 2 to terminate and 
    //collecting the return value...      
    if (pthread_join(tid_2, (void *) &status)) {
        printf("Error joining thread 2");
        exit(1);
    }
        printf("Thread 2 - Return value: %d\n", (int)status );

    return 0;
}

我希望输出像这样:

Thread 1
Thread 2
Thread 1 - Return value: 0
Thread 2 - Return value: 0

但我的问题是返回值Thread 1是733029576,但Thread 2返回0的预测; 就像状态变量未初始化并包含垃圾一样.我错过了什么？

Answer 1

您在输出中看到垃圾值的原因是本地void *status变量state_your_name未初始化:

void *state_your_name(char *name) {
    //Declaration of the variable containing the return status
    void* status = NULL; // <<=====    Add initialization here

    //Printing out the string
    printf("%s\n", name);
    //Exiting the thread and saving the return value
    pthread_exit(status);
}

有了这个改变,你的程序应该产生你期望的输出.

请注意,status直接返回state_your_name是调用的替代方法pthread_exit:您可以使用替换该调用return status.