java - NotifyAll, IllegalMonitorStateException

import java.math.BigInteger;

class Numbers {

    final static int NUMBER = 2;
    final static int POWER = 4;

    static long msecs;
    static BigInteger result;
    static Boolean done = false;

    public static void main(String[] args) {

        BigInteger number = BigInteger.valueOf(NUMBER);
        result = number;

        //Boolean done = false;

        Runnable pow = () -> {
            System.out.println(number + " pow " + POWER + " = " + number.pow(POWER));

            synchronized (done) {
                done = true;
                done.notifyAll();
            }
        };

        Runnable sum = () -> {
            for(int i = 2; i<POWER; i=i*i) {
                result = result.multiply(result);
            }

            System.out.println(number + " sum " + POWER + " = " + result);

            synchronized (done) {
                done = true;
                done.notifyAll();
            }
        };

        Runnable time = () -> {
            for(msecs = 0; true; msecs++) {
                try {
                    Thread.sleep(1);
                } catch(InterruptedException e) {
                    //nic
                }
            }
        };

        Thread timet = new Thread(time);
        Thread sumt = new Thread(sum);
        Thread powt = new Thread(pow);

        timet.start();
        powt.start();

        synchronized (done) {
            while(!done) {
                try {
                    done.wait();
                } catch (InterruptedException e) {
                    //nic
                }
            }
        }

        timet.interrupt();
        powt.interrupt();

        System.out.println("Pow time " + msecs + " msecs.");
        done = false;

        timet.start();
        sumt.start();

        try {
            synchronized (done) {
                while (!done) {
                    done.wait();
                }
            }
        } catch (InterruptedException e) {
            //nic
        }


        timet.interrupt();
        sumt.interrupt();

        System.out.println("Sum time " + msecs + " msecs.");

    }
}

我想检查这两种方法之间的时差，但 done.notifyAll() 不断抛出 IllegalMonitorStateException 。

最佳答案

问题在这里:

synchronized (done) {
    done = true;//<---problem
    done.notifyAll();
}

由于您正在为 done 分配新值，这意味着您正在 notifyAll 上执行 Boolean.TRUE 但您的同步块(synchronized block)正在使用 Boolean.FALSE 的监视器。并且由于 notifyAll 需要线程拥有执行它的对象的监视器，因此它会抛出 IllegalMonitorStateException 。

所以不要更改同步对象的值。还要避免同步所有类(公共(public)常量/文字)可用的对象，因为您冒着其他人有相同想法的风险，并且也会在他们的同步中使用它们，这可能会给您带来一些痛苦。

锁应该只能从它们所属的类内部访问。所以以 Jon Skeet ( What is the difference between synchronized on lockObject and using this as the lock? ) 为例并自行同步

private final Object lock = new Object();