Java多线程设计模式详解学习笔记三——SingleThreadExecution

public class Main {

	public static void main(String[] args) {
		Gate gate=new Gate();
		new UserThread(gate, "Alice", "Alaska").start();
        new UserThread(gate, "Bobby", "Brazil").start();
        new UserThread(gate, "Chris", "Canada").start();
	}
}

public class Gate {

	private int count;
	private String name="Nobody";
	private String address="NoWhere";
	
	void pass(String name,String address){
		count++;
		this.name=name;
		try {
			Thread.sleep(1000);
		} catch (InterruptedException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		this.address=address;
		check();
	}
	
	private void check() {
		if (name.charAt(0)!=address.charAt(0)) {
			System.out.println("********BROKEN*********"+toString());
		}
	}

	@Override
	public String toString() {
		try {
			Thread.sleep(100);
		} catch (InterruptedException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		return "Count:"+count+" Namre:"+name+" Address:"+address;
	}	
}

public class UserThread extends Thread{

	private Gate gate;
	private String name;
	private String address;
	
	public UserThread(Gate gate,String name,String address) {
		this.gate=gate;
		this.name=name;
		this.address=address;
	}
	
	@Override
	public void run() {
		System.out.println(name+"BEGIN");
		while(true){
			gate.pass(name, address);		}
	}
}

运行结构：

AliceBEGIN
BobbyBEGIN
ChrisBEGIN
********BROKEN*********Count:4 Namre:Bobby Address:Canada
********BROKEN*********Count:6 Namre:Alice Address:Alaska
********BROKEN*********Count:6 Namre:Alice Address:Alaska
********BROKEN*********Count:9 Namre:Bobby Address:Brazil
********BROKEN*********Count:10 Namre:Alice Address:Brazil
********BROKEN*********Count:11 Namre:Chris Address:Canada
********BROKEN*********Count:13 Namre:Bobby Address:Canada
********BROKEN*********Count:15 Namre:Alice Address:Alaska
********BROKEN*********Count:15 Namre:Alice Address:Alaska
********BROKEN*********Count:18 Namre:Bobby Address:Brazil
********BROKEN*********Count:19 Namre:Alice Address:Brazil
********BROKEN*********Count:20 Namre:Chris Address:Canada
********BROKEN*********Count:22 Namre:Bobby Address:Canada
********BROKEN*********Count:24 Namre:Alice Address:Alaska
********BROKEN*********Count:24 Namre:Alice Address:Alaska
********BROKEN*********Count:27 Namre:Chris Address:Brazil
********BROKEN*********Count:28 Namre:Alice Address:Brazil

测试无法证明安全性：如果测试时找到错误，标明写好的程序并不安全。但是就算测试时没有找到错误也不能保证程序一定是安全的。当测试的次数不够，时间点部队，就可能检查不到问题。
在程序中Gate是SharedResource（共享资源），需要进行共享互斥的操作

public class Gate {

	private int count;
	private String name="Nobody";
	private String address="NoWhere";
	
	synchronized void  pass(String name,String address){
		count++;
		this.name=name;
		try {
			Thread.sleep(1000);
		} catch (InterruptedException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		this.address=address;
		check();
	}
	
	private void check() {
		if (name.charAt(0)!=address.charAt(0)) {
			System.out.println("********BROKEN*********"+toString());
		}
	}

	@Override
	public synchronized String toString() {
		try {
			Thread.sleep(100);
		} catch (InterruptedException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		return "Count:"+count+" Namre:"+name+" Address:"+address;
	}	
}

运行结果：

BobbyBEGIN
AliceBEGIN
ChrisBEGIN

check()方法也有name和address字段，为什么没有加synchronized：

因为pass方法调用check()方法，而pass方法已经synchronized了，而check方法又是private的，所以不会有其他线程同时调用这个方法。

看到synchronized时就要思考这个synchronized是在保护什么。