适用的情况
不想让各个线程随意的访问实例, 保持实例的安全性, 但是又想在保证安全性同时提高响应速度.
实现的方式
如果实例处于非正确的状态, 不等待实例恢复正确, 而是直接返回.
- 判断检测实例的状态是不正确的.
- 通过return语句返回.
- 通过throw抛出一个异常中断执行.
相关的模式
- 如果线程需要等待正常的数据返回, 那么可以使用Guarded Suspension模式.
代码示例:
这是一个每隔一段时间自动保存数据的代码, 如果内容没有变化, 那么保存数据的线程可以直接return,无需等待数据的更改之后进行保存,然后再返回.
package com.graphic.balking;
import java.io.FileWriter;
import java.io.IOException;
import java.io.Writer;
public class Data {
private final String fileName;
private String content;
private boolean changed;
public Data(String fileName, String content){
this.fileName = fileName;
this.content = content;
this.changed = true;
}
public synchronized void change(String newContent){
content = newContent;
changed = true;
}
public synchronized void save() throws IOException{
if (!changed){
return;
}
doSave();
changed = false;
}
private void doSave() throws IOException{
System.out.println(Thread.currentThread().getName() + "Calls doSave , content = " + content);
Writer writer = new FileWriter(fileName);
writer.write(content);
writer.close();
}
}
package com.graphic.balking;
import java.io.IOException;
public class SaverThread extends Thread{
private final Data data;
public SaverThread(String name, Data data){
super(name);
this.data = data;
}
@Override
public void run() {
try {
while (true){
data.save();
Thread.sleep(1000);
}
}catch (IOException | InterruptedException e){
e.printStackTrace();
}
}
}
package com.graphic.balking;
import java.io.IOException;
import java.util.Random;
public class ChangerThread extends Thread{
private final Data data;
private final Random random = new Random();
public ChangerThread(String name, Data data){
super(name);
this.data = data;
}
@Override
public void run(){
try{
for (int i = 0; true; i++) {
data.change("No." + i);
Thread.sleep(random.nextInt(10000));
data.save();
}
}catch (IOException | InterruptedException e){
e.printStackTrace();
}
}
}
package com.graphic.balking;
public class Main {
public static void main(String[] args) {
Data data = new Data("balkingTest", "this si first");
new ChangerThread("changer-1", data).start();
new SaverThread("saver-1", data).start();
}
}
