多线程与高并发(9)——死锁

当两个线程互相等待对方的监视器时会发生死锁，所有线程处于阻塞状态，无法运行。在系统有多个监视器的情况下，死锁是很容易发生的。

class A {
    public synchronized void foo(B b) {
        System.out.println("Thread:" + Thread.currentThread().getName()
                + "run in foo() method of instance A");
        try {
            Thread.sleep(200);
        } catch (InterruptedException ex) {
            ex.printStackTrace();
        }
        System.out.println("Thread:" + Thread.currentThread().getName()
                + "call last() of B class");
        b.last();
    }

    public synchronized void last() {
        System.out.println("last() of A...");
    }
}

class B {
    public synchronized void bar(A a) {
        System.out.println("Thread:" + Thread.currentThread().getName()
                + "run in bar() method of instance B");
        try {
            Thread.sleep(200);
        } catch (InterruptedException ex) {
            ex.printStackTrace();
        }
        System.out.println("Thread:" + Thread.currentThread().getName()
                + "call last() of A class");
        a.last();

    }

    public synchronized void last() {
        System.out.println("last() of B...");
    }
}

public class DeadLock implements Runnable {
    A a = new A();
    B b = new B();

    public void init() {
        Thread.currentThread().setName("main Thread");
        a.foo(b);
        System.out.println("run in main Thread...");
    }

    @Override
    public void run() {
        Thread.currentThread().setName("dut Thread");
        b.bar(a);
        System.out.println("run in main Thread...");
    }

    public void main() {
        DeadLock d = new DeadLock();
        new Thread(d).start();
        d.init();
    }
}