【安卓笔记】AsyncTask源码剖析

public abstract class AsyncTask<Params, Progress, Result> 

public static final Executor THREAD_POOL_EXECUTOR
            = new ThreadPoolExecutor(CORE_POOL_SIZE, MAXIMUM_POOL_SIZE, KEEP_ALIVE,
                    TimeUnit.SECONDS, sPoolWorkQueue, sThreadFactory);

 private static final int CORE_POOL_SIZE = 5;
    private static final int MAXIMUM_POOL_SIZE = 128;
    private static final int KEEP_ALIVE = 1;
    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());
        }
    };
    private static final BlockingQueue<Runnable> sPoolWorkQueue =
            new LinkedBlockingQueue<Runnable>(10);

/**
     * 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 class SerialExecutor implements Executor {
        final ArrayDeque<Runnable> mTasks = new ArrayDeque<Runnable>();
        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);
            }
        }
    }

private static final int MESSAGE_POST_RESULT = 0x1;//当前消息类型--->任务完成消息
    private static final int MESSAGE_POST_PROGRESS = 0x2;//当前消息类型-->进度消息
    private static final InternalHandler sHandler = new InternalHandler();
    private static volatile Executor sDefaultExecutor = SERIAL_EXECUTOR;//默认线程池
    private final WorkerRunnable<Params, Result> mWorker;
    private final FutureTask<Result> mFuture;
    private volatile Status mStatus = Status.PENDING;//当前状态
    
    private final AtomicBoolean mCancelled = new AtomicBoolean();
    private final AtomicBoolean mTaskInvoked = new AtomicBoolean();

 public enum Status {
        /**
         * Indicates that the task has not been executed yet.
         */
        PENDING,//等待执行
        /**
         * Indicates that the task is running.
         */
        RUNNING,//执行
        /**
         * Indicates that {@link AsyncTask#onPostExecute} has finished.
         */
        FINISHED,//执行结束
    }

 private static class InternalHandler extends Handler {
        @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 void finish(Result result) {
        if (isCancelled()) {
            onCancelled(result);
        } else {
            onPostExecute(result);
        }
        mStatus = Status.FINISHED;
    }

 public final AsyncTask<Params, Progress, Result> execute(Params... params) {
        return executeOnExecutor(sDefaultExecutor, params);
    }

 public final AsyncTask<Params, Progress, Result> 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;
    }

 mFuture = new FutureTask<Result>(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 occured while executing doInBackground()",
                            e.getCause());
                } catch (CancellationException e) {
                    postResultIfNotInvoked(null);
                }
            }
        };

  private static abstract class WorkerRunnable<Params, Result> implements Callable<Result> {
        Params[] mParams;
    }
 mWorker = new WorkerRunnable<Params, Result>() {
            public Result call() throws Exception {
                mTaskInvoked.set(true);
                Process.setThreadPriority(Process.THREAD_PRIORITY_BACKGROUND);
                //noinspection unchecked
                return postResult(doInBackground(mParams));
            }
        };

 private Result postResult(Result result) {
        @SuppressWarnings("unchecked")
        Message message = sHandler.obtainMessage(MESSAGE_POST_RESULT,
                new AsyncTaskResult<Result>(this, result));
        message.sendToTarget();
        return result;
    }

 private static class AsyncTaskResult<Data> {
        final AsyncTask mTask;
        final Data[] mData;
        AsyncTaskResult(AsyncTask task, Data... data) {
            mTask = task;
            mData = data;
        }
    }

 protected final void publishProgress(Progress... values) {
        if (!isCancelled()) {
            sHandler.obtainMessage(MESSAGE_POST_PROGRESS,
                    new AsyncTaskResult<Progress>(this, values)).sendToTarget();
        }
    }