【安卓笔记】HandlerThread源码剖析

package com.example.handlethreaddemo;
import android.app.Activity;
import android.os.Bundle;
import android.os.Handler;
import android.os.HandlerThread;
import android.os.Looper;
import android.os.Message;
import android.util.Log;
public class MainActivity extends Activity
{
	private Looper mLooper;
	private MyHandler mHandler;
	private static final String TAG = "MainActivity";
	private static class MyHandler extends Handler
	{
		public MyHandler(Looper looper)
		{
			super(looper);
		}
		@Override
		public void handleMessage(Message msg)
		{
			switch (msg.what)
			{
			case 1:
				Log.i(TAG, "当前线程是"+Thread.currentThread().getName()+",TEST 1");
				break;
			case 2:
				Log.i(TAG, "TEST 2");
				break;
			}
		}
	}
	
	@Override
	protected void onCreate(Bundle savedInstanceState)
	{
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);
		
		//创建HandlerThread对象
		HandlerThread myHandleThread = new HandlerThread("HandlerThread<子线程>");
		//启动HandlerThread---->内部将启动消息循环
		myHandleThread.start();
		//获取Looper
		mLooper = myHandleThread.getLooper();
		//构造Handler，传入子线程中的Looper
		mHandler = new MyHandler(mLooper);
		/*
		 * 注：经过上述步骤，Handler将绑定子线程的Looper和MessageQueue.
		 * 也就是说handleMessage最终由子线程调用
		 * */
		mHandler.sendEmptyMessage(1);
		
		Log.i(TAG,"当前线程是:"+Thread.currentThread().getName());
		
	}
	
	
}

使用HandlerThread内部提供的Looper对象构造Handler对象，然后在ui线程中向Handler发送消息。log日志如下：

int mPriority;//优先级
 int mTid = -1;//线程标志
 Looper mLooper;//消息循环

 public HandlerThread(String name, int priority) {
        super(name);
        mPriority = priority;
    }

 public void run() {
        mTid = Process.myTid();
        Looper.prepare();//创建Looper对象
        synchronized (this) {
            mLooper = Looper.myLooper();//获取与本线程绑定的Looper
            notifyAll();
        }
        Process.setThreadPriority(mPriority);
        onLooperPrepared();//回调接口，默认为空实现。
        Looper.loop();//启动消息循环--->may be blocked
        mTid = -1;
    }

 public Looper getLooper() {
        if (!isAlive()) {//线程死亡
            return null;
        }
        
        // If the thread has been started, wait until the looper has been created.
        synchronized (this) {
            while (isAlive() && mLooper == null) {
                try {
                    wait();//异步等待Looper准备好
                } catch (InterruptedException e) {
                }
            }
        }
        return mLooper;
    }

 public boolean quit() {
        Looper looper = getLooper();
        if (looper != null) {
            looper.quit();//内部调用looper类的quit
            return true;
        }
        return false;
    }

public static void prepare() {
        prepare(true);
    }
    private static void prepare(boolean quitAllowed) {
        if (sThreadLocal.get() != null) {
            throw new RuntimeException("Only one Looper may be created per thread");
        }
        sThreadLocal.set(new Looper(quitAllowed));
    }

public static Looper myLooper() {
        return sThreadLocal.get();
    }

public static void loop() {
        final Looper me = myLooper();
        if (me == null) {
            throw new RuntimeException("No Looper; Looper.prepare() wasn't called on this thread.");
        }
        final MessageQueue queue = me.mQueue;
        // Make sure the identity of this thread is that of the local process,
        // and keep track of what that identity token actually is.
        Binder.clearCallingIdentity();
        final long ident = Binder.clearCallingIdentity();
        for (;;) {
            Message msg = queue.next(); // might block
            if (msg == null) {
                // No message indicates that the message queue is quitting.
                return;
            }
            // This must be in a local variable, in case a UI event sets the logger
            Printer logging = me.mLogging;
            if (logging != null) {
                logging.println(">>>>> Dispatching to " + msg.target + " " +
                        msg.callback + ": " + msg.what);
            }
            msg.target.dispatchMessage(msg);
            if (logging != null) {
                logging.println("<<<<< Finished to " + msg.target + " " + msg.callback);
            }
            // Make sure that during the course of dispatching the
            // identity of the thread wasn't corrupted.
            final long newIdent = Binder.clearCallingIdentity();
            if (ident != newIdent) {
                Log.wtf(TAG, "Thread identity changed from 0x"
                        + Long.toHexString(ident) + " to 0x"
                        + Long.toHexString(newIdent) + " while dispatching to "
                        + msg.target.getClass().getName() + " "
                        + msg.callback + " what=" + msg.what);
            }
            msg.recycle();
        }
    }