package android.os; import android.annotation.NonNull; import android.annotation.Nullable; /** * Handy class for starting a new thread that has a looper. The looper can then be * used to create handler classes. Note that start() must still be called. */ public class HandlerThread extends Thread { //线程优先级 int mPriority; //线程ID int mTid = -1; //当前线程持有的Looper对象 Looper mLooper; //包含当前 Looper 对象的 Handler private @Nullable Handler mHandler; public HandlerThread(String name) { super(name); //使用默认的线程优先级 mPriority = Process.THREAD_PRIORITY_DEFAULT; } public HandlerThread(String name, int priority) { super(name); //使用自定义的线程优先级 mPriority = priority; } //在 Looper 循环启动前调用 //此处是空实现，留待子类重写 protected void onLooperPrepared() { } @Override public void run() { mTid = Process.myTid(); //触发当前线程创建 Looper 对象 Looper.prepare(); synchronized (this) { //获取 Looper 对象 mLooper = Looper.myLooper(); //唤醒在等待的线程 //唤醒 getLooer() 中可能还处于等待状态的线程 notifyAll(); } //设置线程优先级 Process.setThreadPriority(mPriority); onLooperPrepared(); //开启消息循环 Looper.loop(); mTid = -1; } //获取与当前线程关联的 Looper 对象 //因为 getLooper() 方法可能先于 run() 被调用，此时就需要先等待 Looper 对象被创建 public Looper getLooper() { //如果当前线程未在运行，则返回 null if (!isAlive()) { return null; } synchronized (this) { //如果当前线程已处理运行状态（已调用 start() 方法）且 Looper 对象还未创建 //则调用 wait() 方法释放锁，等待 Looper 对象创建 while (isAlive() && mLooper == null) { try { wait(); } catch (InterruptedException e) { } } } return mLooper; } /** * @return a shared {@link Handler} associated with this thread * @hide */ @NonNull public Handler getThreadHandler() { if (mHandler == null) { mHandler = new Handler(getLooper()); } return mHandler; } //清空消息队列中所有的消息 public boolean quit() { Looper looper = getLooper(); if (looper != null) { looper.quit(); return true; } return false; } //清空消息队列中所有非延时消息 public boolean quitSafely() { Looper looper = getLooper(); if (looper != null) { looper.quitSafely(); return true; } return false; } /** * Returns the identifier of this thread. See Process.myTid(). */ public int getThreadId() { return mTid; } }