问题描述

多线程IllegalMonitorStateException 很简单的代码，感觉没错啊！

 public class Test implements Runnable {
    Mysynchronized syn=null;
    static Boolean b=true;
    public Test(Mysynchronized syn) {
        this.syn=syn;
    }
    public static void main(String[] args) {
        Mysynchronized syn=new Mysynchronized();
        new Thread(new Test(syn),"xx").start();
        new Thread(new Test(syn),"yy").start();
    }

    @Override
    public void run() {
        while (true) {
            synchronized (syn) {
                System.out.println(Thread.currentThread().getName());
                if(b){
                    b=false;
                    try {
                        wait();
                    } catch (InterruptedException e) {
                        // TODO Auto-generated catch block
                        e.getMessage();
                    }
                }else {
                    b=true;
                    notify();
                }

            }

        }
    }

}

运行结果如下：xx
Exception in thread "xx" Exception in thread "yy" yy
java.lang.IllegalMonitorStateException
at java.lang.Object.notify(Native Method)
at the_eight_chapter.Test.run(Test.java:30)
at java.lang.Thread.run(Unknown Source)
java.lang.IllegalMonitorStateException
at java.lang.Object.wait(Native Method)
at java.lang.Object.wait(Unknown Source)
at the_eight_chapter.Test.run(Test.java:23)
at java.lang.Thread.run(Unknown Source)

解决方案

wait和notify 方法调用的不对，在前面加上syn就可以了。
切记wait和notify是针对特定对象的。

 public class Test implements Runnable {
    Mysynchronized syn = null;
    static Boolean b = true;

    public Test(Mysynchronized syn) {
        this.syn = syn;
    }

    public static void main(String[] args) {
        Mysynchronized syn = new Mysynchronized();
        new Thread(new Test(syn), "xx").start();
        new Thread(new Test(syn), "yy").start();
    }

    @Override
    public void run() {
        while (true) {
            synchronized (syn) {
                System.out.println(Thread.currentThread().getName());
                if (b) {
                    b = false;
                    try {
                        syn.wait();
                    } catch (InterruptedException e) {
                        // TODO Auto-generated catch block
                        e.getMessage();
                    }
                } else {
                    b = true;
                    syn.notify();
                }

            }

        }
    }

}

解决方案二：

这会死锁吧
 synchronized (syn) {
                System.out.println(Thread.currentThread().getName());
                if(b){
                    b=false;
                    try {
                        wait();//进了这里，进入了wait,run方法没有执行完，其他线程都进不了run的这段代码，该线程无法唤醒。
                    } catch (InterruptedException e) {
                        // TODO Auto-generated catch block
                        e.getMessage();
                    }
                }else {
                    b=true;
                    notify();
                }

            }