消息系统模型

0 参考

Android中消息系统模型和Handler Looper

Android Handler机制

1 理论知识

1 handler消息机制是用于线程通信的，不是更新UI的。 2 主线程属于消费者，子线程属于生产者

当消息队列已满，停止生产（子线程阻塞)

当消息队列被掏空，停止消费（主线程阻塞） 3 消息队列不是无限制的。最大50，android源码。 4 同类唤醒异常 5 那个线程调用prepare，就会关联一个looper对象 6 [java并发编程--互斥锁, 读写锁及条件](http://coolxing.iteye.com/blog/1236909) 7 线程数据隔离 ThreadLocal [正确理解ThreadLocal](http://www.iteye.com/topic/103804) ## 2 模拟代码 Handler类： public class Handler { Looper mLopper; MessageQueue queue; public Handler() { mLopper = Looper.myLooper(); queue = mLopper.messageQueue; } public void sendMessage(Message msg) { msg.target=this; this.queue.enqueueMessage(msg); } public void dispatchMessage(Message msg) { handleMessage(msg); } public void handleMessage(Message msg) { } Looper类： public class Looper { public static final ThreadLocal sThreadLocal = new ThreadLocal<>(); public MessageQueue messageQueue; private Looper() { messageQueue = new MessageQueue(); } public static Looper myLooper() { return sThreadLocal.get(); } public static void prepare() throws Exception { if (sThreadLocal.get() != null) { throw new Exception(); } sThreadLocal.set(new Looper()); } public static void looper() throws Exception { Looper mylooper = myLooper(); if (mylooper==null){ throw new Exception(""); } MessageQueue queue=mylooper.messageQueue; for (;;){ Message msg=queue.next(); if (msg==null){ continue; } msg.target.dispatchMessage(msg); } } } MessageQueue类 public class MessageQueue { Message[] items; int putIndex; int takeIndex; int count; Lock lock;//互斥锁，2个条件同步 Condition noempoty; Condition nofull; public MessageQueue() { this.items = new Message[50]; lock = new ReentrantLock(); noempoty=lock.newCondition(); nofull=lock.newCondition(); } //生产大于消费会覆盖 public void enqueueMessage(Message msg) { try { lock.lock(); while (count == items.length) { //子线程阻塞 try { nofull.await(); } catch (InterruptedException e) { e.printStackTrace(); } } this.items[putIndex] = msg; putIndex = (++putIndex == items.length) ? 0 : putIndex; count++; noempoty.signalAll(); } finally { lock.unlock(); } } public Message next() { Message msg = null; try { lock.lock(); while (count == 0) { //主线程 try { noempoty.await(); } catch (InterruptedException e) { e.printStackTrace(); } } msg = items[takeIndex]; items[takeIndex] = null; takeIndex = (++takeIndex == items.length) ? 0 : takeIndex; count--; //消费通知生产 nofull.signalAll(); } finally { lock.unlock(); } return msg; } Message类 public class Message { Handler target;//发送消息handler,保护属性 int what; Object obj; public Message() { } } 测试类 public class Test { public static void main(String[] args) throws Exception { System.out.println("stat"); Looper.prepare(); final Handler handler=new Handler(){ @Override public void handleMessage(Message msg) { System.out.println(msg.obj.toString()); } }; for (int i=0;i<10;i++){ Thread thread=new Thread(new Runnable() { @Override public void run() { try { Thread.sleep(1000); } catch (InterruptedException e) { e.printStackTrace(); } Message msg=new Message(); msg.what=10; synchronized (UUID.class){ msg.obj=Thread.currentThread().getName()+ UUID.randomUUID().toString(); } handler.sendMessage(msg); } }); thread.setName("thread"+i+"---->>"); thread.start(); } Looper.looper(); }