如何知道其他线程是否已完成？

class MyThread extends Thread {
    @Override
    public void run() {
        // 执行线程体
    }
}

public class Main {
    public static void main(String[] args) {
        MyThread myThread = new MyThread();
        myThread.start();
        try {
            myThread.join();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

import threading

class MyThread(threading.Thread):
    def run(self):
        # 执行线程体
        pass

my_thread = MyThread()
my_thread.start()
my_thread.join()

#include <iostream>
#include <thread>

void my_func() {
    // 执行线程体
}

int main() {
    std::thread my_thread(my_func);
    my_thread.join();
    return 0;
}