在过去的几天里,我一直在阅读关于多线程的文章,并且使用多线程技术遇到了一个简单的任务。这是任务:为什么此代码中的同步功能无法正常工作?
创建一个模拟50米跑步比赛的应用程序(在我的代码中他们是10,无所谓)。跑步者的数量应该是5,你应该给每个跑步者的线程命名。打印赢家。所有其他线程也应完成比赛。打印每位参赛选手完成比赛的时间并突出赢家的时间。
这是我写的代码:
public class Racer implements Runnable {
public static String winner;
public static int time = 0;
public void incrementTime() {
synchronized (Racer.class) {
time++;
}
}
public void race() {
for (int distance = 1; distance <= 10; distance++) {
incrementTime();
System.out.println("Distance covered by " + Thread.currentThread().getName() + " is " + distance + " meters.");
boolean finalDest = this.isTheRaceOver(distance);
if (finalDest) {
break;
}
}
}
private boolean isTheRaceOver(int finalDistance) {
boolean isRaceOver = false;
if (Racer.winner == null && finalDistance == 10) {
String winnerName = Thread.currentThread().getName();
Racer.winner = winnerName;
System.out.println("The winner is : " + Racer.winner + " with time " + time);
isRaceOver = true;
} else if (Racer.winner == null) {
isRaceOver = false;
} else if (finalDistance != 10) {
isRaceOver = false;
} else if (finalDistance == 10) {
System.out.println(Thread.currentThread().getName() + " is with time " + time);
}
return isRaceOver;
}
@Override
public void run() {
this.race();
}
}
public class RacerDemo {
public static void main(String[] args) {
Racer racer = new Racer();
Thread a = new Thread(racer, "A");
Thread b = new Thread(racer, "B");
Thread c = new Thread(racer, "C");
Thread d = new Thread(racer, "D");
Thread e = new Thread(racer, "E");
a.start();
b.start();
c.start();
d.start();
e.start();
}
}
一个输出是:
Distance covered by A is 1 meters. Distance covered by C is 1 meters. Distance covered by C is 2 meters. Distance covered by C is 3 meters. Distance covered by C is 4 meters. Distance covered by C is 5 meters. Distance covered by C is 6 meters. Distance covered by C is 7 meters. Distance covered by C is 8 meters. Distance covered by C is 9 meters. Distance covered by C is 10 meters. The winner is : C with time 12 // should be 11 ? Distance covered by B is 1 meters. Distance covered by B is 2 meters. ...... and so on
困扰我的是,当它打印每个车手(线程)所花费的时间的事情掩盖了距离,它并没有显示正确的时间。我使incrementTime()同步,但程序无法正常工作。你能告诉我什么是错的吗?我的错误在哪里?
这个解释是正确的。我不知道为什么这是downvoted。 –
是的,我知道问题来自race(),但几分钟前我试图在for循环内创建一个同步块,它似乎正常工作..我跑了几次..但谢谢! – Roxy