//AsyncTask是個(gè)抽象類
public abstract class AsyncTask<Params, Progress, Result> {
  private static final String LOG_TAG = "AsyncTask";

  //Cpu數(shù)量胡陪，創(chuàng)建線程池使用
  private static final int CPU_COUNT = Runtime.getRuntime().availableProcessors();
  //核心線程合陵，創(chuàng)建線程池使用
    private static final int CORE_POOL_SIZE = CPU_COUNT + 1;
  //最大線程數(shù)量，創(chuàng)建線程池使用
    private static final int MAXIMUM_POOL_SIZE = CPU_COUNT * 2 + 1;
  //存活時(shí)間聚请，創(chuàng)建線程池使用
    private static final int KEEP_ALIVE = 1;

  //創(chuàng)建線程的工廠sThreadFactory伞广，創(chuàng)建線程池使用
  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());
      }
  };

  //存放Runnable任務(wù)的隊(duì)列堰塌，創(chuàng)建線程池使用
  private static final BlockingQueue<Runnable> sPoolWorkQueue =
          new LinkedBlockingQueue<Runnable>(128);


  //創(chuàng)建線程池THREAD_POOL_EXECUTOR, 實(shí)現(xiàn)多線程并行
  public static final Executor THREAD_POOL_EXECUTOR
          = new ThreadPoolExecutor(CORE_POOL_SIZE, MAXIMUM_POOL_SIZE, KEEP_ALIVE,
                  TimeUnit.SECONDS, sPoolWorkQueue, sThreadFactory);

  //自定義的串行線程池
  public static final Executor SERIAL_EXECUTOR = new SerialExecutor();

  //Message種類:發(fā)送結(jié)果
  private static final int MESSAGE_POST_RESULT = 0x1;
  //Message種類:發(fā)送進(jìn)度
  private static final int MESSAGE_POST_PROGRESS = 0x2;

  //默認(rèn)的線程池:串行的線程池
  private static volatile Executor sDefaultExecutor = SERIAL_EXECUTOR;
    
  //內(nèi)部的Handler
  private static InternalHandler sHandler;

  //WorkerRunnable是自定義的Callable，從參數(shù)猜測是用來存放傳進(jìn)來的參數(shù)和傳出去的結(jié)果
  private final WorkerRunnable<Params, Result> mWorker;
  
  //FutureTask是繼承至RunableFuture琼牧，可接收一個(gè)callable為參數(shù)恢筝，可以有返回結(jié)果，而且里面cancel(boolean mayInterruptIfRunning)可以取消任務(wù)
  private final FutureTask<Result> mFuture;

  //事件狀態(tài)
  private volatile Status mStatus = Status.PENDING;
  
  //是否取消任務(wù)
  private final AtomicBoolean mCancelled = new AtomicBoolean();
  
  //標(biāo)識任務(wù)是否被執(zhí)行過  
  private final AtomicBoolean mTaskInvoked = new AtomicBoolean();
    
  //串行的線程池巨坊，保證串行順序執(zhí)行任務(wù)
  private static class SerialExecutor implements Executor {
      final ArrayDeque<Runnable> mTasks = new ArrayDeque<Runnable>();
      Runnable mActive;

      public synchronized void execute(final Runnable r) {//將 Runnable加入到隊(duì)列中撬槽，再THREAD_POOL_EXECUTOR處理Runnable
          mTasks.offer(new Runnable() {
              public void run() {
                  try {
                      r.run();
                  } finally {//上面執(zhí)行完畢后才能執(zhí)行下一個(gè)任務(wù)
                      scheduleNext();
                  }
              }
          });
          if (mActive == null) {
              scheduleNext();
          }
      }

      protected synchronized void scheduleNext() {
          if ((mActive = mTasks.poll()) != null) {
              THREAD_POOL_EXECUTOR.execute(mActive);//使用THREAD_POOL_EXECUTOR處理Runnable
          }
      }
  }

  /**
   * Indicates the current status of the task. Each status will be set only once
   * during the lifetime of a task.
   * 每一種狀態(tài)只能改變一次，也就是說整個(gè)生命周期只能執(zhí)行一次任務(wù)
   */
  public enum Status {
      /**
       * Indicates that the task has not been executed yet.
       */
      PENDING,//待定狀態(tài)
      /**
       * Indicates that the task is running.
       */
      RUNNING,//執(zhí)行狀態(tài)
      /**
       * Indicates that {@link AsyncTask#onPostExecute} has finished.
       */
      FINISHED,//結(jié)束狀態(tài)
  }

  private static Handler getHandler() {
      synchronized (AsyncTask.class) {
          if (sHandler == null) {
              sHandler = new InternalHandler();//這里直接new Handler(),說明是在UI線程中進(jìn)行的趾撵，所以AsyncTask要在主線程初始化
          }
          return sHandler;
      }
  }

  /** @hide */
  public static void setDefaultExecutor(Executor exec) {//設(shè)置默認(rèn)線程池侄柔，可選串行和并行
      sDefaultExecutor = exec;
  }

  /**
   * Creates a new asynchronous task. This constructor must be invoked on the UI thread.
   */
  public AsyncTask() {  
      
      //mWork是繼承自callable，封裝成執(zhí)行doInBackground的單位
      mWorker = new WorkerRunnable<Params, Result>() {  
          public Result call() throws Exception {
              mTaskInvoked.set(true);//任務(wù)被執(zhí)行了

              Process.setThreadPriority(Process.THREAD_PRIORITY_BACKGROUND);//設(shè)置線程優(yōu)先級是后臺線程
              //noinspection unchecked
              Result result = doInBackground(mParams);//執(zhí)行doInBackground(),并保存結(jié)果
              Binder.flushPendingCommands();
              return postResult(result);//將結(jié)果發(fā)送出去
          }
      };
      //FutureTask使用Callable作為構(gòu)造函數(shù)的參數(shù)
      mFuture = new FutureTask<Result>(mWorker) {
          @Override
          protected void done() {
              try {
                  postResultIfNotInvoked(get());//返回結(jié)果: 如果mTaskInvoked==true占调，則不會返回結(jié)果暂题，因?yàn)樵趍Worker里面已經(jīng)返回了
              } 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);//取消執(zhí)行
              }
          }
      };
  }

  private void postResultIfNotInvoked(Result result) {
      final boolean wasTaskInvoked = mTaskInvoked.get();//檢查是否執(zhí)行過
      if (!wasTaskInvoked) {//未執(zhí)行過
          postResult(result);
      }
  }

  private Result postResult(Result result) {//將結(jié)果封裝在Message，發(fā)送給Handler處理
      @SuppressWarnings("unchecked")
      Message message = getHandler().obtainMessage(MESSAGE_POST_RESULT,
              new AsyncTaskResult<Result>(this, result));//將結(jié)果給內(nèi)部Handler處理
      message.sendToTarget();
      return result;
  }

  /**
   * Returns the current status of this task.
   * 
   * @return The current status.
   * 獲取目前狀態(tài)
   */
  public final Status getStatus() {
      return mStatus;
  }

  @WorkerThread //執(zhí)行的方法究珊，在線程池處理
  protected abstract Result doInBackground(Params... params);


  @MainThread //執(zhí)行前調(diào)用薪者，在UI線程執(zhí)行
  protected void onPreExecute() {
  }

  @SuppressWarnings({"UnusedDeclaration"})
  @MainThread  //執(zhí)行后調(diào)用，在UI線程執(zhí)行
  protected void onPostExecute(Result result) {
  }

  @SuppressWarnings({"UnusedDeclaration"})
  @MainThread //進(jìn)度改變剿涮，在UI線程執(zhí)行
  protected void onProgressUpdate(Progress... values) {
  }


  @SuppressWarnings({"UnusedParameters"})
  //  //執(zhí)行取消后調(diào)用的方法
  @MainThread 
  protected void onCancelled(Result result) {
      onCancelled();
  }    
  
  //執(zhí)行取消后調(diào)用的方法
  @MainThread  
  protected void onCancelled() {
  }

  /**
   * 檢查任務(wù)是否取消
   */
  public final boolean isCancelled() {
      return mCancelled.get();
  }

  /**
   * 取消任務(wù)
   */
  public final boolean cancel(boolean mayInterruptIfRunning) {
      mCancelled.set(true);
      return mFuture.cancel(mayInterruptIfRunning);
      //取消mFuture任務(wù)言津，不需要發(fā)送信息給handler，因?yàn)閙Future結(jié)束后取试，也會發(fā)送postResult給Handler悬槽，
      //Handler就可以根據(jù)mCancelled進(jìn)行處理
  }

  /**
   * 獲取任務(wù)執(zhí)行的結(jié)果
   */
  public final Result get() throws InterruptedException, ExecutionException {
      return mFuture.get();
  }

  /**
   * 最多等待為使計(jì)算完成所給定的時(shí)間之后,檢索其結(jié)果(如果結(jié)果可用),則返回
   */
  public final Result get(long timeout, TimeUnit unit) throws InterruptedException,
          ExecutionException, TimeoutException {
      return mFuture.get(timeout, unit);
  }

  /**
   * execute調(diào)用executeOnExecutor
   */
  @MainThread
  public final AsyncTask<Params, Progress, Result> execute(Params... params) {
      return executeOnExecutor(sDefaultExecutor, params);//使用默認(rèn)的線程池
  }

  /**
   * 分析的入口
   */
  @MainThread
  public final AsyncTask<Params, Progress, Result> executeOnExecutor(Executor exec,
          Params... params) {
      //檢查狀態(tài)
      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)");
          }
      }
      //將狀態(tài)設(shè)置為運(yùn)行，在workRunnable執(zhí)行的時(shí)候也會設(shè)置為running狀態(tài)
      mStatus = Status.RUNNING;
      
      //可見onPreExecute是在主線程進(jìn)行
      onPreExecute();
      //將參數(shù)也賦進(jìn)去
      mWorker.mParams = params;
      
      //加入線程池執(zhí)行
      exec.execute(mFuture);

      return this;
  }
  
//如果參數(shù)是runnable瞬浓，直接通過默認(rèn)的線程池執(zhí)行初婆，跟普通線程池運(yùn)行差不多
  @MainThread
  public static void execute(Runnable runnable) {
      sDefaultExecutor.execute(runnable);
  }

  /**
   * 改變進(jìn)度，可以在doInbackground調(diào)用
   */
  @WorkerThread
  protected final void publishProgress(Progress... values) {
      if (!isCancelled()) {
          getHandler().obtainMessage(MESSAGE_POST_PROGRESS,
                  new AsyncTaskResult<Progress>(this, values)).sendToTarget();
      }
  }

  //任務(wù)結(jié)束，這個(gè)方法是在Handler里面調(diào)用
  private void finish(Result result) {
      if (isCancelled()) {
          onCancelled(result);//執(zhí)行取消
      } else {
          onPostExecute(result);//任務(wù)完成
      }
      mStatus = Status.FINISHED;
  }

  //內(nèi)部定義的Handler
  private static class InternalHandler extends Handler {
      public InternalHandler() {
          super(Looper.getMainLooper());//獲取Looper
      }

      @SuppressWarnings({"unchecked", "RawUseOfParameterizedType"})
      @Override
      public void handleMessage(Message msg) {//對AsyncTaskResult進(jìn)行處理
          AsyncTaskResult<?> result = (AsyncTaskResult<?>) msg.obj;
          switch (msg.what) {
              case MESSAGE_POST_RESULT://任務(wù)結(jié)束
                  // There is only one result
                  result.mTask.finish(result.mData[0]);
                  break;
              case MESSAGE_POST_PROGRESS://改變進(jìn)度
                  result.mTask.onProgressUpdate(result.mData);
                  break;
          }
      }
  }

  //自定義的帶有參數(shù)的Callable
  private static abstract class WorkerRunnable<Params, Result> implements Callable<Result> {
      Params[] mParams;
  }
  
  //封裝的返回結(jié)果磅叛，主要給handler使用的
  @SuppressWarnings({"RawUseOfParameterizedType"})
  private static class AsyncTaskResult<Data> {
      final AsyncTask mTask;
      final Data[] mData;

      AsyncTaskResult(AsyncTask task, Data... data) {
          mTask = task;
          mData = data;
      }
  }
}

總結(jié): 好累屑咳，下次再總結(jié)吧...