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。