java - 如何暂停 main() 直到所有其他线程都死了？

Question

在我的程序中，我在 main() 方法中创建了几个线程。 main 方法的最后一行是对 System.out.println() 的调用，我不想在所有线程都死掉之前调用它。我尝试在每个线程上调用 Thread.join() ，但是这会阻塞每个线程，以便它们按顺序执行而不是并行执行。

有没有办法阻塞 main() 线程，直到所有其他线程完成执行？这是我的代码的相关部分:

public static void main(String[] args) {

//some other initialization code

//Make array of Thread objects
Thread[] racecars = new Thread[numberOfRaceCars];

//Fill array with RaceCar objects
for(int i=0; i<numberOfRaceCars; i++) {
    racecars[i] = new RaceCar(laps, args[i]);
}

//Call start() on each Thread
for(int i=0; i<numberOfRaceCars; i++) {
    racecars[i].start();
    try {
        racecars[i].join(); //This is where I tried to using join()
                            //It just blocks all other threads until the current                            
                            //thread finishes.
    } catch(InterruptedException e) {
        e.printStackTrace();
    }
}

//This is the line I want to execute after all other Threads have finished
System.out.println("It's Over!");

}

感谢大家的帮助!

埃里克

Answer 1

您启动线程并立即等待它们完成(使用 join())。相反，您应该在另一个 for 循环中的 for 循环之外执行 join()，例如:

// start all threads
for(int i=0; i<numberOfRaceCars; i++) {
    racecars[i].start();
}
// threads run... we could yield explicity to allow the other threads to execute
// before we move on, all threads have to finish
for(int i=0; i<numberOfRaceCars; i++) {
    racecars[i].join(); // TODO Exception handling
}
// now we can print
System.out.println("It's over!");