HandlerThread
public class HandlerThread extends Thread {
int mPriority;
int mTid = -1;
Looper mLooper;
public HandlerThread(String name) {
super(name);
mPriority = Process.THREAD_PRIORITY_DEFAULT;
}
public HandlerThread(String name, int priority) {
super(name);
mPriority = priority;
}
/**
* Call back method that can be explicitly overridden if needed to execute some
* setup before Looper loops.
* 模版方法模式
*/
protected void onLooperPrepared() {
}
@Override
public void run() {
mTid = Process.myTid();
Looper.prepare();
synchronized (this) {
mLooper = Looper.myLooper();
notifyAll();
}
Process.setThreadPriority(mPriority);
onLooperPrepared();
Looper.loop();
mTid = -1;
}
public Looper getLooper() {
if (!isAlive()) {
return null;
}
boolean wasInterrupted = false;
// If the thread has been started, wait until the looper has been created.
synchronized (this) {
while (isAlive() && mLooper == null) {
try {
wait();
} catch (InterruptedException e) {
wasInterrupted = true;
}
}
}
/*
* We may need to restore the thread's interrupted flag, because it may
* have been cleared above since we eat InterruptedExceptions
*/
if (wasInterrupted) {
Thread.currentThread().interrupt();
}
return mLooper;
}
/**
* Quits the handler thread's looper.
*
* Causes the handler thread's looper to terminate without processing any
* more messages in the message queue.
*
* Any attempt to post messages to the queue after the looper is asked to quit will fail.
* For example, the {@link Handler#sendMessage(Message)} method will return false.
*
* Using this method may be unsafe because some messages may not be delivered
* before the looper terminates. Consider using {@link #quitSafely} instead to ensure
* that all pending work is completed in an orderly manner.
*
* @return True if the looper looper has been asked to quit or false if the
* thread had not yet started running.
*/
public boolean quit() {
Looper looper = getLooper();
if (looper != null) {
looper.quit();
return true;
}
return false;
}
/**
* Quits the handler thread's looper safely.
*
* Causes the handler thread's looper to terminate as soon as all remaining messages
* in the message queue that are already due to be delivered have been handled.
* Pending delayed messages with due times in the future will not be delivered.
*
* Any attempt to post messages to the queue after the looper is asked to quit will fail.
* For example, the {@link Handler#sendMessage(Message)} method will return false.
*
* If the thread has not been started or has finished, then false is returned.
* Otherwise the looper is asked to quit and true is returned.
*
* @return True if the looper looper has been asked to quit or false if the
* thread had not yet started running.
*/
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;
}
}
IntentService
IntentService 受 Android 8.0（API 级别 26）施加的所有后台执行限制的约束。 考虑使用 androidx.work.WorkManager 或 androidx.core.app.JobIntentService，它们在 Android 8.0 或更高版本上运行时使用作业而不是服务
public abstract class IntentService extends Service {
private volatile Looper mServiceLooper;
@UnsupportedAppUsage
private volatile ServiceHandler mServiceHandler;
private String mName;
private final class ServiceHandler extends Handler {
public ServiceHandler(Looper looper) {
super(looper);
}
@Override
public void handleMessage(Message msg) {
onHandleIntent((Intent)msg.obj);
stopSelf(msg.arg1);
}
}
public IntentService(String name) {
super();
mName = name;
}
@Override
public void onCreate() {
super.onCreate();
HandlerThread thread = new HandlerThread("IntentService[" + mName + "]");
thread.start();
mServiceLooper = thread.getLooper();
mServiceHandler = new ServiceHandler(mServiceLooper);
}
@Override
public void onStart(@Nullable Intent intent, int startId) {
Message msg = mServiceHandler.obtainMessage();
msg.arg1 = startId;
msg.obj = intent;
mServiceHandler.sendMessage(msg);
}
/**
* You should not override this method for your IntentService. Instead,
* override {@link #onHandleIntent}, which the system calls when the IntentService
* receives a start request.
* @see android.app.Service#onStartCommand
*/
@Override
public int onStartCommand(@Nullable Intent intent, int flags, int startId) {
onStart(intent, startId);
return mRedelivery ? START_REDELIVER_INTENT : START_NOT_STICKY;
}
@Override
public void onDestroy() {
mServiceLooper.quit();
}
/**
* Unless you provide binding for your service, you don't need to implement this
* method, because the default implementation returns null.
* @see android.app.Service#onBind
*/
@Override
@Nullable
public IBinder onBind(Intent intent) {
return null;
}
@WorkerThread
protected abstract void onHandleIntent(@Nullable Intent intent);
}
AsyncTask
AsyncTask是一种轻量级的异步任务类，它可以在线程池中执行后台任务，然后把执行的进度和最终结果传递给主线程并在主线程中更新UI
从实现上来说，AsyncTask封装了ThreadPool和Handler，通过AsyncTask可以更加方便地执行后台任务以及在主线程中访问UI
但是AsyncTask并不适合进行特别耗时的后台任务，对于特别耗时的任务来说，建议使用线程池
AsyncTask中有两个线程池(SerialExecutor和THREAD_POOL_EXECUTOR)和一个Handler(InternalHandler)
其中线程池SerialExecutor用于任务的排队，而线程池THREAD_POOL_EXECUTOR用于真正地执行任务
InternalHandler用于将执行环境从线程池切换到主线程
AsyncTask目前是过期状态，官方建议使用java.util.concurrent 或者 kotlin coroutines 或者 Dart中的async、await、Future
记得调用cancel。某些情况下我们只能实现逻辑cancel，即使我们正确地调用了cancel也未必能真正地取消任务，因为如果在doInBackgroud里有一个不可中断的操作，比如BitmapFactory.decodeStream()，那么这个操作会继续下去
参考文档
android.googlesource.com/platform/fr…
juejin.cn/post/684490…
blog.csdn.net/cpcpcp123/a…
