linux - 为什么 pthread_self() 会多次返回相同的 id？

Question

我正在尝试在 for 循环中创建多个线程(代表人员)，并显示作为参数传递的人员 ID 以及线程 ID。人员 ID 按预期显示，但线程 ID 始终相同。

#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>

void* travelers(void* arg) {
    int* person_id = (int*) arg;
    printf("\nPerson %d was created, TID = %d", *person_id, pthread_self());
}

int main(int argc, char** argv)
{
    int i;
    pthread_t th[1000];

    for (i=0; i < 10; i++) {
        if ((pthread_create(&th[i], NULL, travelers, &i)) != 0) {
            perror("Could not create threads");
            exit(2);
        }
        else {
            // Join thread
            pthread_join(th[i], NULL);
        }
    }
    printf("\n");

    return 0;
}

我得到的输出是这样的:

Person 0 was created, TID = 881035008
Person 1 was created, TID = 881035008
Person 2 was created, TID = 881035008
Person 3 was created, TID = 881035008
Person 4 was created, TID = 881035008
Person 5 was created, TID = 881035008
Person 6 was created, TID = 881035008
Person 7 was created, TID = 881035008
Person 8 was created, TID = 881035008
Person 9 was created, TID = 881035008

我做错了什么？

Answer 1

由于一次只有一个创建的线程运行，每个新线程都获得与之前完成的线程相同的 ID，即 ID 只是被重复使用。尝试在循环中创建线程，然后在第二个循环中加入它们。

然而，你将不得不注意每个线程独立读取i的内容，这会给你带来不同的头痛。我会将索引作为上下文参数传递，然后将其转换为线程函数内的 int。