package test.android; /** * 异步任务 * * @param * @param * @param */ public abstract class AsyncTask { private static final String LOG_TAG = "AsyncTask"; private static final int CPU_COUNT = Runtime.getRuntime().availableProcessors(); // 我们希望在核心池中至少有2个线程，最多4个线程。, // 宁愿比cpu计数少1，以避免使cpu充满后台工作。 /** * 核心线程数 */ private static final int CORE_POOL_SIZE = Math.max(2, Math.min(CPU_COUNT - 1, 4)); /** * 最大线程数 */ private static final int MAXIMUM_POOL_SIZE = CPU_COUNT * 2 + 1; /** * 线程回收时间 */ private static final int KEEP_ALIVE_SECONDS = 30; /** * 执行程序创建新线程时使用的工厂 */ private static final ThreadFactory sThreadFactory = new ThreadFactory() { private final AtomicInteger mCount = new AtomicInteger(1); public Thread newThread(Runnable r) { return new Thread(r, "AsyncTask #" + mCount.getAndIncrement()); } }; /** * 任务较多时暂存到队列 */ private static final BlockingQueue sPoolWorkQueue = new LinkedBlockingQueue(128); /** * An {@link Executor} that can be used to execute tasks in parallel. */ public static final Executor THREAD_POOL_EXECUTOR; static { ThreadPoolExecutor threadPoolExecutor = new ThreadPoolExecutor( CORE_POOL_SIZE, MAXIMUM_POOL_SIZE, KEEP_ALIVE_SECONDS, TimeUnit.SECONDS, sPoolWorkQueue, sThreadFactory); threadPoolExecutor.allowCoreThreadTimeOut(true); THREAD_POOL_EXECUTOR = threadPoolExecutor; } /** * An {@link Executor} that executes tasks one at a time in serial * order. This serialization is global to a particular process. */ public static final Executor SERIAL_EXECUTOR = new SerialExecutor(); private static final int MESSAGE_POST_RESULT = 0x1; private static final int MESSAGE_POST_PROGRESS = 0x2; private static volatile Executor sDefaultExecutor = SERIAL_EXECUTOR; private static InternalHandler sHandler; private final WorkerRunnable mWorker; private final FutureTask mFuture; private volatile Status mStatus = Status.PENDING; private final AtomicBoolean mCancelled = new AtomicBoolean(); private final AtomicBoolean mTaskInvoked = new AtomicBoolean(); private final Handler mHandler; private static class SerialExecutor implements Executor { final ArrayDeque mTasks = new ArrayDeque(); Runnable mActive; public synchronized void execute(final Runnable r) { mTasks.offer(new Runnable() { public void run() { try { r.run(); } finally { scheduleNext(); } } }); if (mActive == null) { scheduleNext(); } } protected synchronized void scheduleNext() { if ((mActive = mTasks.poll()) != null) { THREAD_POOL_EXECUTOR.execute(mActive); } } } /** * 指示任务的当前状态.在任务的生命周期内每个状态将只设置一次. * Indicates the current status of the task. Each status will be set only once * during the lifetime of a task. */ public enum Status { /** * Indicates that the task has not been executed yet. * 指示任务尚未执行 */ PENDING, /** * Indicates that the task is running. * 指示任务正在运行 */ RUNNING, /** * Indicates that {@link AsyncTask#onPostExecute} has finished. * 表示任务已经完成 */ FINISHED, } private static Handler getMainHandler() { synchronized (AsyncTask.class) { if (sHandler == null) { sHandler = new InternalHandler(Looper.getMainLooper()); } return sHandler; } } private Handler getHandler() { return mHandler; } /** * @hide */ public static void setDefaultExecutor(Executor exec) { sDefaultExecutor = exec; } /** * Creates a new asynchronous task. This constructor must be invoked on the UI thread. * 主线程中创建的异步任务 */ public AsyncTask() { this((Looper) null); } /** * Creates a new asynchronous task. This constructor must be invoked on the UI thread. * 主线程中创建的异步任务 * * @hide */ public AsyncTask(@Nullable Handler handler) { this(handler != null ? handler.getLooper() : null); } /** * Creates a new asynchronous task. This constructor must be invoked on the UI thread. * 主线程中创建的异步任务 * * @hide */ public AsyncTask(@Nullable Looper callbackLooper) { mHandler = callbackLooper == null || callbackLooper == Looper.getMainLooper() ? getMainHandler() : new Handler(callbackLooper); mWorker = new WorkerRunnable() { public Result call() throws Exception { mTaskInvoked.set(true); Result result = null; try { Process.setThreadPriority(Process.THREAD_PRIORITY_BACKGROUND); //noinspection unchecked result = doInBackground(mParams); Binder.flushPendingCommands(); } catch (Throwable tr) { mCancelled.set(true); throw tr; } finally { postResult(result); } return result; } }; mFuture = new FutureTask(mWorker) { @Override protected void done() { try { postResultIfNotInvoked(get()); } catch (InterruptedException e) { android.util.Log.w(LOG_TAG, e); } catch (ExecutionException e) { throw new RuntimeException("An error occurred while executing doInBackground()", e.getCause()); } catch (CancellationException e) { postResultIfNotInvoked(null); } } }; } private void postResultIfNotInvoked(Result result) { final boolean wasTaskInvoked = mTaskInvoked.get(); if (!wasTaskInvoked) { postResult(result); } } private Result postResult(Result result) { @SuppressWarnings("unchecked") Message message = getHandler().obtainMessage(MESSAGE_POST_RESULT, new AsyncTaskResult(this, result)); message.sendToTarget(); return result; } /** * Returns the current status of this task. * 获取当前任务的执行状态 * * @return The current status. */ public final Status getStatus() { return mStatus; } /** * Override this method to perform a computation on a background thread. The * specified parameters are the parameters passed to {@link #execute} * by the caller of this task. * 在异步线程中执行的方法 * * This method can call {@link #publishProgress} to publish updates * on the UI thread. * * @param params The parameters of the task. * @return A result, defined by the subclass of this task. * @see #onPreExecute() * @see #onPostExecute * @see #publishProgress */ @WorkerThread protected abstract Result doInBackground(Params... params); /** * Runs on the UI thread before {@link #doInBackground}. * 任务执行前执行,在主线程执行 * * @see #onPostExecute * @see #doInBackground */ @MainThread protected void onPreExecute() { } /** * Runs on the UI thread after {@link #doInBackground}. The * specified result is the value returned by {@link #doInBackground}. * 任务完成后执行的方法,在主线程中执行 * This method won't be invoked if the task was cancelled. * 如果任务被取消，此方法将不会被调用。 * * @param result The result of the operation computed by {@link #doInBackground}. * 异步任务返回的结果 * @see #onPreExecute * @see #doInBackground * @see #onCancelled(Object) */ @SuppressWarnings({"UnusedDeclaration"}) @MainThread protected void onPostExecute(Result result) { } /** * Runs on the UI thread after {@link #publishProgress} is invoked. * The specified values are the values passed to {@link #publishProgress}. * 执行在主线程中,用于更新进度展示. * * @param values The values indicating progress. * @see #publishProgress * @see #doInBackground */ @SuppressWarnings({"UnusedDeclaration"}) @MainThread protected void onProgressUpdate(Progress... values) { } /** * Runs on the UI thread after {@link #cancel(boolean)} is invoked and * {@link #doInBackground(Object[])} has finished. * 执行在主线程中,当cancel方法调用或者doInBackground方法调用 * * The default implementation simply invokes {@link #onCancelled()} and * ignores the result. If you write your own implementation, do not call * super.onCancelled(result). * * @param result The result, if any, computed in * {@link #doInBackground(Object[])}, can be null * @see #cancel(boolean) * @see #isCancelled() */ @SuppressWarnings({"UnusedParameters"}) @MainThread protected void onCancelled(Result result) { onCancelled(); } /** * Applications should preferably override {@link #onCancelled(Object)}. * This method is invoked by the default implementation of * {@link #onCancelled(Object)}. * * Runs on the UI thread after {@link #cancel(boolean)} is invoked and * {@link #doInBackground(Object[])} has finished. * * @see #onCancelled(Object) * @see #cancel(boolean) * @see #isCancelled() */ @MainThread protected void onCancelled() { } /** * Returns true if this task was cancelled before it completed * normally. If you are calling {@link #cancel(boolean)} on the task, * the value returned by this method should be checked periodically from * {@link #doInBackground(Object[])} to end the task as soon as possible. *任务是否取消 * @return true if task was cancelled before it completed * @see #cancel(boolean) */ public final boolean isCancelled() { return mCancelled.get(); } /** * Attempts to cancel execution of this task. This attempt will * fail if the task has already completed, already been cancelled, * or could not be cancelled for some other reason. If successful, * and this task has not started when cancel is called, * this task should never run. If the task has already started, * then the mayInterruptIfRunning parameter determines * whether the thread executing this task should be interrupted in * an attempt to stop the task. * * Calling this method will result in {@link #onCancelled(Object)} being * invoked on the UI thread after {@link #doInBackground(Object[])} * returns. Calling this method guarantees that {@link #onPostExecute(Object)} * is never invoked. After invoking this method, you should check the * value returned by {@link #isCancelled()} periodically from * {@link #doInBackground(Object[])} to finish the task as early as * possible. * * @param mayInterruptIfRunning true if the thread executing this * task should be interrupted; otherwise, in-progress tasks are allowed * to complete. * @return false if the task could not be cancelled, * typically because it has already completed normally; * true otherwise * @see #isCancelled() * @see #onCancelled(Object) */ public final boolean cancel(boolean mayInterruptIfRunning) { mCancelled.set(true); return mFuture.cancel(mayInterruptIfRunning); } /** * Waits if necessary for the computation to complete, and then * retrieves its result. * * @return The computed result. * @throws CancellationException If the computation was cancelled. * @throws ExecutionException If the computation threw an exception. * @throws InterruptedException If the current thread was interrupted * while waiting. */ public final Result get() throws InterruptedException, ExecutionException { return mFuture.get(); } /** * Waits if necessary for at most the given time for the computation * to complete, and then retrieves its result. * * @param timeout Time to wait before cancelling the operation. * @param unit The time unit for the timeout. * @return The computed result. * @throws CancellationException If the computation was cancelled. * @throws ExecutionException If the computation threw an exception. * @throws InterruptedException If the current thread was interrupted * while waiting. * @throws TimeoutException If the wait timed out. */ public final Result get(long timeout, TimeUnit unit) throws InterruptedException, ExecutionException, TimeoutException { return mFuture.get(timeout, unit); } /** * Executes the task with the specified parameters. The task returns * itself (this) so that the caller can keep a reference to it. * * Note: this function schedules the task on a queue for a single background * thread or pool of threads depending on the platform version. When first * introduced, AsyncTasks were executed serially on a single background thread. * Starting with {@link android.os.Build.VERSION_CODES#DONUT}, this was changed * to a pool of threads allowing multiple tasks to operate in parallel. Starting * {@link android.os.Build.VERSION_CODES#HONEYCOMB}, tasks are back to being * executed on a single thread to avoid common application errors caused * by parallel execution. If you truly want parallel execution, you can use * the {@link #executeOnExecutor} version of this method * with {@link #THREAD_POOL_EXECUTOR}; however, see commentary there for warnings * on its use. * * This method must be invoked on the UI thread. * * @param params The parameters of the task. * @return This instance of AsyncTask. * @throws IllegalStateException If {@link #getStatus()} returns either * {@link Status#RUNNING} or {@link Status#FINISHED}. * @see #executeOnExecutor(java.util.concurrent.Executor, Object[]) * @see #execute(Runnable) */ @MainThread public final AsyncTask execute(Params... params) { return executeOnExecutor(sDefaultExecutor, params); } /** * Executes the task with the specified parameters. The task returns * itself (this) so that the caller can keep a reference to it. * * This method is typically used with {@link #THREAD_POOL_EXECUTOR} to * allow multiple tasks to run in parallel on a pool of threads managed by * AsyncTask, however you can also use your own {@link Executor} for custom * behavior. * * Warning: Allowing multiple tasks to run in parallel from * a thread pool is generally not what one wants, because the order * of their operation is not defined. For example, if these tasks are used * to modify any state in common (such as writing a file due to a button click), * there are no guarantees on the order of the modifications. * Without careful work it is possible in rare cases for the newer version * of the data to be over-written by an older one, leading to obscure data * loss and stability issues. Such changes are best * executed in serial; to guarantee such work is serialized regardless of * platform version you can use this function with {@link #SERIAL_EXECUTOR}. * * This method must be invoked on the UI thread. * * @param exec The executor to use. {@link #THREAD_POOL_EXECUTOR} is available as a * convenient process-wide thread pool for tasks that are loosely coupled. * @param params The parameters of the task. * @return This instance of AsyncTask. * @throws IllegalStateException If {@link #getStatus()} returns either * {@link Status#RUNNING} or {@link Status#FINISHED}. * @see #execute(Object[]) */ @MainThread public final AsyncTask executeOnExecutor(Executor exec, Params... params) { if (mStatus != Status.PENDING) { switch (mStatus) { case RUNNING: throw new IllegalStateException("Cannot execute task:" + " the task is already running."); case FINISHED: throw new IllegalStateException("Cannot execute task:" + " the task has already been executed " + "(a task can be executed only once)"); } } mStatus = Status.RUNNING; onPreExecute(); mWorker.mParams = params; exec.execute(mFuture); return this; } /** * Convenience version of {@link #execute(Object...)} for use with * a simple Runnable object. See {@link #execute(Object[])} for more * information on the order of execution. * * @see #execute(Object[]) * @see #executeOnExecutor(java.util.concurrent.Executor, Object[]) */ @MainThread public static void execute(Runnable runnable) { sDefaultExecutor.execute(runnable); } /** * This method can be invoked from {@link #doInBackground} to * publish updates on the UI thread while the background computation is * still running. Each call to this method will trigger the execution of * {@link #onProgressUpdate} on the UI thread. * * {@link #onProgressUpdate} will not be called if the task has been * canceled. * * @param values The progress values to update the UI with. * @see #onProgressUpdate * @see #doInBackground */ @WorkerThread protected final void publishProgress(Progress... values) { if (!isCancelled()) { getHandler().obtainMessage(MESSAGE_POST_PROGRESS, new AsyncTaskResult(this, values)).sendToTarget(); } } private void finish(Result result) { if (isCancelled()) { onCancelled(result); } else { onPostExecute(result); } mStatus = Status.FINISHED; } private static class InternalHandler extends Handler { public InternalHandler(Looper looper) { super(looper); } @SuppressWarnings({"unchecked", "RawUseOfParameterizedType"}) @Override public void handleMessage(Message msg) { AsyncTaskResult result = (AsyncTaskResult) msg.obj; switch (msg.what) { case MESSAGE_POST_RESULT: // There is only one result result.mTask.finish(result.mData[0]); break; case MESSAGE_POST_PROGRESS: result.mTask.onProgressUpdate(result.mData); break; } } } private static abstract class WorkerRunnable implements Callable { Params[] mParams; } @SuppressWarnings({"RawUseOfParameterizedType"}) private static class AsyncTaskResult { final AsyncTask mTask; final Data[] mData; AsyncTaskResult(AsyncTask task, Data... data) { mTask = task; mData = data; } } }
