android 2.3之后,真正的Android团队在Async任务中做了什么更改.当我执行以下代码时,在Android 2.3和3.0中都得到相同的结果.

package com.sample.asynctask;

import android.app.Activity;
import android.os.AsyncTask;
import android.os.Bundle;
import android.util.Log;

public class AsyncTaskTestActivity extends Activity {
    private static final String TAG = "AsyncTaskTestActivity";

    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        //ExecutorService executorService = Executors.newFixedThreadPool(1);
        for (int i = 1; i <= 20; i++) {
            TestTask testTask = new TestTask(i);
            testTask.execute();
        }
    }

    private static class TestTask extends AsyncTask<Void, Integer, Void> {
        int i;
        public TestTask(int i) {
            Log.i(TAG, "Constructor for " + i);
            this.i = i;
        }

        @Override
        protected void onPreExecute() {
            // TODO Auto-generated method stub
            super.onPreExecute();
            Log.i(TAG, "onPreExecute for " + i);
        }

        @Override
        protected Void doInBackground(Void... params) {
            Log.i(TAG, i + " Thread goes to sleep");
            try {
                Thread.sleep(20000);
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            Log.i(TAG, i + " Thread wakes up");
            return null;
        }

        @Override
        protected void onPostExecute(Void result) {
            // TODO Auto-generated method stub
            super.onPostExecute(result);
            Log.i(TAG, "onPostExecute for " + i);
        }
    }
}

我在Gingerbread中的假设：5异步任务一次在一个线程池中执行.
我在Honeycomb中的假设是：1异步任务一次在一个线程池中执行.就像并发执行一样.

但是,Gingerbread和Honeycomb都同时执行5个Async任务.

而且,当Async任务的数量增加到140.i时,我也没有得到java.util.concurrent.RejectedExecutionException.

我的假设是否正确？里面到底发生了什么？

解决方法:

我的假设是否正确？

您的假设是正确的.

里面到底发生了什么？

android.os.AsyncTask内部的默认执行程序：

... ...

private static volatile Executor sDefaultExecutor = SERIAL_EXECUTOR;

... ...

已在android.app.ActivityThread中重置：

... ...

// If the app is Honeycomb MR1 or earlier, switch its AsyncTask
// implementation to use the pool executor.  Normally, we use the
// serialized executor as the default. This has to happen in the
// main thread so the main looper is set right.
if (data.appInfo.targetSdkVersion <= android.os.Build.VERSION_CODES.HONEYCOMB_MR1) {
    AsyncTask.setDefaultExecutor(AsyncTask.THREAD_POOL_EXECUTOR);
}

... ...

Android Gingerbread之后,异步任务实际上发生了什么变化？

请查看AsyncTask change history,更具体地说,这是一个：

Mar 17, 2011 – AsyncTask now uses the poll executor for apps up through HC MR1 and t…

当异步任务的数量增加到140时,我没有得到java.util.concurrent.RejectedExecutionException.

这是任务总数和每个任务执行时间的一个因素,在另一个世界中,任务总数为140(大于128),但是,在任何给定时间由线程池分配的线程总数较小而不是128,换句话说,您的情况下总是有一些空闲线程(由于上一个任务已完成并释放了资源).您可以尝试增加每个任务的执行时间,例如Thread.sleep(10000),这可能会给您RejectedExecutionException.