NotifyAll,IllegalMonitorStateException

Question

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间差异,但done.notifyAll()不断抛出IllegalMonitorStateException.

Answer 1

问题在这里:

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

既然你要分配新的值done就意味着你正在执行notifyAll的Boolean.TRUE,但您的同步块正在使用的显示器Boolean.FALSE.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.

因此,请勿更改同步对象的值.还要避免在可用于所有类(公共常量/文字)的对象上进行同步,因为您冒着其他人会有相同想法的风险,并且还会在同步中使用它们,这可能会让您感到痛苦.

锁只能从类中属于它们才能访问.所以从Jon Skeet中获取示例(lockObject上的synchronized和使用它作为锁之间的区别是什么？)并自行同步

private final Object lock = new Object();