1 public class AsyncTaskDemo  extends AsyncTask<String, Integer, String>{
 2     private final static String TAG = "AsyncTaskTest";
 3
 4     @Override
 5     protected String doInBackground(String... params) {
 6         Log.v(TAG, params[0] + "=================doInBackground===================PID = " + Thread.currentThread().getId());
 7
 8         return params[0];
 9     }
10
11
12 }

1 // 一个按钮的onclick函数
2 public void test(View view) {
3         Log.v("AsyncTaskTest", "CPU_COUNT = " + Runtime.getRuntime().availableProcessors());
4
5         new AsyncTaskDemo().execute("Hello1");
6         new AsyncTaskDemo().execute("Hello2");
7         new AsyncTaskDemo().execute("Hello3");
8         new AsyncTaskDemo().execute("Hello4");
9     }

//logcat里打印出来的结果12-11 16:07:34.865    1979-1979/com.sabo.helloworld V/AsyncTaskTest﹕ CPU_COUNT = 1
12-11 16:07:34.871    1979-2102/com.sabo.helloworld V/AsyncTaskTest﹕ Hello1=================doInBackground===================PID = 161
12-11 16:07:34.872    1979-2103/com.sabo.helloworld V/AsyncTaskTest﹕ Hello2=================doInBackground===================PID = 162
12-11 16:07:34.872    1979-2103/com.sabo.helloworld V/AsyncTaskTest﹕ Hello3=================doInBackground===================PID = 162
12-11 16:07:34.872    1979-2103/com.sabo.helloworld V/AsyncTaskTest﹕ Hello4=================doInBackground===================PID = 162

1     @MainThread
2     public final AsyncTask<Params, Progress, Result> execute(Params... params) {
3         return executeOnExecutor(sDefaultExecutor, params);
4     }

    @MainThreadpublic 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);// exec  --> sDefaultExecutorreturn this;}

public static final Executor SERIAL_EXECUTOR = new SerialExecutor();private static volatile Executor sDefaultExecutor = SERIAL_EXECUTOR;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);}}}

1         new AsyncTaskDemo().execute("Hello1"); //mActive == null
2         new AsyncTaskDemo().execute("Hello2"); //mActive != null
3         new AsyncTaskDemo().execute("Hello3"); //mActive != null
4         new AsyncTaskDemo().execute("Hello4"); //mActive != null

1     private static final int CORE_POOL_SIZE = CPU_COUNT + 1;
2     private static final int MAXIMUM_POOL_SIZE = CPU_COUNT * 2 + 1;
3     private static final int KEEP_ALIVE = 1;
4
5     public static final Executor THREAD_POOL_EXECUTOR
6             = new ThreadPoolExecutor(CORE_POOL_SIZE, MAXIMUM_POOL_SIZE, KEEP_ALIVE,
7                     TimeUnit.SECONDS, sPoolWorkQueue, sThreadFactory);