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 blocke.printStackTrace();}this.address=address;check();}private void check() {if (name.charAt(0)!=address.charAt(0)) {System.out.println("********BROKEN*********"+toString());}}@Overridepublic String toString() {try {Thread.sleep(100);} catch (InterruptedException e) {// TODO Auto-generated catch blocke.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;}@Overridepublic void run() {System.out.println(name+"BEGIN");while(true){gate.pass(name, address);}}}

运行结构：

AliceBEGINBobbyBEGINChrisBEGIN********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 blocke.printStackTrace();}this.address=address;check();}private void check() {if (name.charAt(0)!=address.charAt(0)) {System.out.println("********BROKEN*********"+toString());}}@Overridepublic synchronized String toString() {try {Thread.sleep(100);} catch (InterruptedException e) {// TODO Auto-generated catch blocke.printStackTrace();}return "Count:"+count+" Namre:"+name+" Address:"+address;}}

运行结果：

BobbyBEGINAliceBEGINChrisBEGIN

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。