JAVA高级之线程死锁问题

线程死锁问题

 不同的线程分别占用对方需要的同步资源不放弃，都在等待对方放弃自己需要的同步资源，就形成了线程的死锁。

package com.cn.java2;

class A {
     
	public synchronized void foo(B b) {
       //这里的同步锁为 this：A类的对象a
		System.out.println("当前线程名: " + Thread.currentThread().getName()
				+ " 进入了A实例的foo方法"); // ①
		try {
     
			Thread.sleep(200);
		} catch (InterruptedException ex) {
     
			ex.printStackTrace();
		}
		System.out.println("当前线程名: " + Thread.currentThread().getName()
				+ " 企图调用B实例的last方法"); // ③
		b.last();
	}

	public synchronized void last() {
      //同步监视器 a
		System.out.println("进入了A类的last方法内部");
	}
}

class B {
     
	public synchronized void bar(A a) {
      //同步监视器：b
		System.out.println("当前线程名: " + Thread.currentThread().getName()
				+ " 进入了B实例的bar方法"); // ②
		try {
     
			Thread.sleep(200);
		} catch (InterruptedException ex) {
     
			ex.printStackTrace();
		}
		System.out.println("当前线程名: " + Thread.currentThread().getName()
				+ " 企图调用A实例的last方法"); // ④
		a.last();
	}

	public synchronized void last() {
     
		System.out.println("进入了B类的last方法内部"); //同步监视器：b
	}
}

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

	public void init() {
     
		Thread.currentThread().setName("主线程");
		// 调用a对象的foo方法
		a.foo(b);
		System.out.println("进入了主线程之后");
	}

	public void run() {
     
		Thread.currentThread().setName("副线程");
		// 调用b对象的bar方法
		b.bar(a);
		System.out.println("进入了副线程之后");
	}

	public static void main(String[] args) {
     
		DeadLock dl = new DeadLock();
		new Thread(dl).start();
		dl.init();
	}
}

package com.cn.java2;

public class ThreadTest2 {
     
    public static void main(String[] args) {
     
        StringBuffer s1 = new StringBuffer();
        StringBuffer s2 = new StringBuffer();

        new Thread() {
     
            @Override
            public void run() {
     

                synchronized (s1) {
     

                    s1.append("a");
                    s2.append("1");

                    try {
     
                        Thread.sleep(100);
                    } catch (InterruptedException e) {
     
                        e.printStackTrace();
                    }
                    synchronized (s2) {
     
                        s1.append("b");
                        s2.append("2");

                        System.out.println(s1);
                        System.out.println(s2);
                    }
                }
            }
        }.start();

        new Thread(new Runnable() {
     
            @Override
            public void run() {
     

                synchronized (s2) {
     

                    s1.append("c");
                    s2.append("3");

                    try {
     
                        Thread.sleep(100);
                    } catch (InterruptedException e) {
     
                        e.printStackTrace();
                    }

                    synchronized (s1) {
     
                        s1.append("d");
                        s2.append("4");

                        System.out.println(s1);
                        System.out.println(s2);
                    }
                }
            }
        }).start();
    }
}