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 ChrisBEGINcheck()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。