Java多线程设计模式详解学习笔记六——Balking

public class Main { public static void main(String[] args) { Data data=new Data("data.txt","(empty)"); new ChangerThread("ChangerThread", data).start(); new SaverThread("SaverThread", data).start(); } }public class Data { private 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; } //若有资料修改，就存储到档案里 public synchronized void save() throws IOException { if (!changed) { System.out.println(Thread.currentThread().getName()+" balks"); return; } doSave(); changed=false; } //实际保存内容的方法 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(); } }public class ChangerThread extends Thread{ private Data data; private Random random=new Random(); public ChangerThread(String name,Data data) { super(name); this.data=data; } @Override public void run() { for (int i = 0; true; i++) { data.change("No."+i); try { Thread.sleep(random.nextInt(1000));//模拟去做其他的事情 data.save(); } catch (InterruptedException e) { // TODO Auto-generated catch block e.printStackTrace(); } catch (IOException e) { // TODO Auto-generated catch block e.printStackTrace(); } } } }public class SaverThread extends Thread{ private Data data; public SaverThread(String name,Data data) { super(name); this.data=data; } @Override public void run() { while(true){ try { data.save(); Thread.sleep(1000); } catch (IOException e) { // TODO Auto-generated catch block e.printStackTrace(); } catch (InterruptedException e) { // TODO Auto-generated catch block e.printStackTrace(); } } } }

运行结果：

SaverThread calls doSave,content =No.0 ChangerThread balks ChangerThread calls doSave,content =No.1 SaverThread calls doSave,content =No.2 ChangerThread balks ChangerThread calls doSave,content =No.3 ChangerThread calls doSave,content =No.4 SaverThread calls doSave,content =No.5 ChangerThread balks SaverThread calls doSave,content =No.6 ChangerThread balks ChangerThread calls doSave,content =No.7 SaverThread calls doSave,content =No.8 ChangerThread balks ChangerThread calls doSave,content =No.9 SaverThread calls doSave,content =No.10 ChangerThread balks ChangerThread calls doSave,content =No.11 SaverThread calls doSave,content =No.12 ChangerThread balks ChangerThread calls doSave,content =No.13 SaverThread calls doSave,content =No.14 ChangerThread balks ChangerThread calls doSave,content =No.15 SaverThread calls doSave,content =No.16GuardedObject(被警戒对象的)参与者：

GuardedObject参与者是一个拥有被警戒的方法（guardedMethod）的类只要满足警戒条件，就会执行实例的方法。可能还有用来更改实例状态的方法（stateChangingMethod）。Data类就是GuardedObject参与者，save方法与change方法则分别是guardedMethod和stateChangingMethod。在Data中synchronized保护的是：content和changed字段。

Balking Pattern与Guarded Suspension Pattern的中间：

分别对应的模型

if(){ return; }while(){ wait(); }在“balk退出”与“等待到警戒条件为止”两种极端的处理方式之间，还有一种这种的做法——“在条件成立为止之前，等待一段时间”。等待一定的时间，看看警戒条件是不是会成立，如果还是不成立的话，就balk退出。这种方式称为guarded timed,或是简单的称为timeout。obj.wait(1000);
interrupt方法执行时：

对这条线程执行interrupt方法时，被interrupt时，等待区里的线程会（与被调用notify、notifyAll一样），重新获取obj的锁定，并跑出InterruptException。notify、notifyAll是对实例调用的，而interrupt则是对线程调用的。