1、概述android
先來了解一下HandlerThread的幾個特性app
2、使用方式ide
再來看HandlerThread的使用方式函數
建立HandlerThread並調用start()方法,使其在子線程內建立Looper對象oop
HandlerThread handlerThread = new HandlerThread("HandlerThread"); handlerThread.start();
而後以HandlerThread內部的Looper對象爲參數建立一個Handler,經過Handler向子線程發送Message,以此下發耗時任務,消息的接受者與任務的處理者則由回調函數ChildCallback來完成源碼分析
Handler childThreadHandler = new Handler(handlerThread.getLooper(), new ChildCallback()); //Callback 運行於子線程 private class ChildCallback implements Handler.Callback { @Override public boolean handleMessage(Message msg) { //在此能夠進行耗時操做 //若是須要更新UI,則須要經過主線程的Handler來完成 return false; } }
完整的實列代碼以下所示ui
public class MainActivity extends AppCompatActivity { private static final String TAG = "MainActivity"; //Callback 運行於子線程 private class ChildCallback implements Handler.Callback { @Override public boolean handleMessage(Message msg) { //在此能夠進行耗時操做 //若是須要更新UI,則須要經過主線程的Handler來完成 Log.e(TAG, "ChildCallback 當前線程名:" + Thread.currentThread().getName() + " " + "當前線程ID:" + Thread.currentThread().getId()); Log.e(TAG, "耗時任務開始"); try { Thread.sleep(5000); } catch (InterruptedException e) { e.printStackTrace(); } Log.e(TAG, "耗時任務結束"); //通知界面更新UI uiHandler.sendEmptyMessage(1); return false; } } //運行於主線程的Handler,用於更新UI @SuppressLint("HandlerLeak") private Handler uiHandler = new Handler() { @Override public void handleMessage(Message msg) { Log.e(TAG, "uiHandler 當前線程名:" + Thread.currentThread().getName() + " " + "當前線程ID:" + Thread.currentThread().getId()); Toast.makeText(MainActivity.this, "耗時操做完成", Toast.LENGTH_LONG).show(); } }; //用於向子線程發佈耗時任務的Handler private Handler childThreadHandler; private HandlerThread handlerThread; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); handlerThread = new HandlerThread("HandlerThread"); handlerThread.start(); childThreadHandler = new Handler(handlerThread.getLooper(), new ChildCallback()); Log.e(TAG, "onCreate 當前線程名:" + Thread.currentThread().getName() + " " + "當前線程ID:" + Thread.currentThread().getId()); } public void startTask(View view) { childThreadHandler.sendEmptyMessage(1); } @Override protected void onDestroy() { super.onDestroy(); handlerThread.quit(); childThreadHandler.removeCallbacksAndMessages(null); } }
程序運行後的日誌以下所示,能夠看出各個方法在調用時所處的線程this
06-22 02:51:41.779 21977-21977/com.summer.myapplication E/MainActivity: onCreate 當前線程名:main 當前線程ID:2 06-22 02:51:44.927 21977-21995/com.summer.myapplication E/MainActivity: ChildCallback 當前線程名:HandlerThread 當前線程ID:497 06-22 02:51:44.928 21977-21995/com.summer.myapplication E/MainActivity: 耗時任務開始 06-22 02:51:49.930 21977-21995/com.summer.myapplication E/MainActivity: 耗時任務結束 06-22 02:51:49.930 21977-21977/com.summer.myapplication E/MainActivity: uiHandler 當前線程名:main 當前線程ID:2
3、源碼分析線程
先看下HandlerThread的類聲明日誌
Thread的子類
public class HandlerThread extends Thread
兩個構造函數,能夠傳入的參數分別是線程名和線程優先級
public HandlerThread(String name) { super(name); //使用默認的線程優先級 mPriority = Process.THREAD_PRIORITY_DEFAULT; } public HandlerThread(String name, int priority) { super(name); //使用自定義的線程優先級 mPriority = priority; }
看下run() 方法
@Override public void run() { mTid = Process.myTid(); //觸發當前線程建立 Looper 對象 Looper.prepare(); synchronized (this) { //獲取 Looper 對象 mLooper = Looper.myLooper(); //喚醒在等待的線程 //喚醒 getLooer() 中可能還處於等待狀態的線程 notifyAll(); } //設置線程優先級 Process.setThreadPriority(mPriority); onLooperPrepared(); //開啓消息循環 Looper.loop(); mTid = -1; }
Looper.prepare()方法用於爲當前線程建立一個Looper對象,在主線程須要依賴此Looper對象來構建一個Handler對象,經過Handler對象來向子線程下發耗時任務
以後能夠看到有一個同步代碼塊,在當中調用了notifyAll()來喚醒等待線程,那該喚醒的又是那個線程呢?這裏須要明確各個方法是運行於那個線程,run()方法確定是運行在子線程中, 但用於想HandlerThread下發任務的Handler是初始化於主線程,所以getlooper()方法也是運行於主線程的。因爲是兩個不一樣的線程,run()方法和getLooper()的運行前後順序是不明確的,所以getLooper()方法須要確保Looper對象不爲null 時才返回,不然將一直阻塞等待Looper對象初始化完成
//獲取與當前線程關聯的 Looper 對象 //由於 getLooper() 方法可能先於 run() 被調用,此時就須要先等待 Looper 對象被建立 public Looper getLooper() { //若是當前線程未在運行,則返回 null if (!isAlive()) { return null; } synchronized (this) { //若是當前線程已處理運行狀態(已調用 start() 方法)且 Looper 對象還未建立 //則調用 wait() 方法釋放鎖,等待 Looper 對象建立 while (isAlive() && mLooper == null) { try { wait(); } catch (InterruptedException e) { } } } return mLooper; }
Looper對象初始化完成後,就須要調用Looper.loop()來開啓消息循環,至此HandlerThread的初始化操做就完成了
HandlerThread的完整源碼註釋
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 { //線程優先級 int mPriority; //線程ID int mTid = -1; //當前線程持有的Looper對象 Looper mLooper; //包含當前 Looper 對象的 Handler private @Nullable Handler mHandler; public HandlerThread(String name) { super(name); //使用默認的線程優先級 mPriority = Process.THREAD_PRIORITY_DEFAULT; } public HandlerThread(String name, int priority) { super(name); //使用自定義的線程優先級 mPriority = priority; } //在 Looper 循環啓動前調用 //此處是空實現,留待子類重寫 protected void onLooperPrepared() { } @Override public void run() { mTid = Process.myTid(); //觸發當前線程建立 Looper 對象 Looper.prepare(); synchronized (this) { //獲取 Looper 對象 mLooper = Looper.myLooper(); //喚醒在等待的線程 //喚醒 getLooer() 中可能還處於等待狀態的線程 notifyAll(); } //設置線程優先級 Process.setThreadPriority(mPriority); onLooperPrepared(); //開啓消息循環 Looper.loop(); mTid = -1; } //獲取與當前線程關聯的 Looper 對象 //由於 getLooper() 方法可能先於 run() 被調用,此時就須要先等待 Looper 對象被建立 public Looper getLooper() { //若是當前線程未在運行,則返回 null if (!isAlive()) { return null; } synchronized (this) { //若是當前線程已處理運行狀態(已調用 start() 方法)且 Looper 對象還未建立 //則調用 wait() 方法釋放鎖,等待 Looper 對象建立 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; } //清空消息隊列中全部的消息 public boolean quit() { Looper looper = getLooper(); if (looper != null) { looper.quit(); return true; } return false; } //清空消息隊列中全部非延時消息 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; } }