Android AsyncTask 分析内部实现

转载自：http://blog.csdn.net/jjwwmlp456/article/details/38623563

sdk3.0前，使用内部的线程池，多线程并发执行。线程池大小等于5，最大达128

sdk3.0后，使用默认的serial线程池，执行完一个线程，再顺序执行下一个线程。sdk3.0<=current version <= sdk4.3时 线程池大小等于5，最大达128

sdk4.4后线程池大小等于 cpu count + 1，最大值为cpu count * 2 + 1

sdk3.0后有两种线程池的实现，默认为 Serial 线程池

1 public static final Executor SERIAL_EXECUTOR = new SerialExecutor();
2 public static final Executor THREAD_POOL_EXECUTOR
3             = new ThreadPoolExecutor(CORE_POOL_SIZE, MAXIMUM_POOL_SIZE, KEEP_ALIVE,
4                     TimeUnit.SECONDS, sPoolWorkQueue, sThreadFactory);
5 private static volatile Executor sDefaultExecutor = SERIAL_EXECUTOR;
6 public static void setDefaultExecutor(Executor exec) {//设置默认线程池
7         sDefaultExecutor = exec;
8 }  

SerialExecutor ，使用同步锁，一次执行一个线程

 1 private static class SerialExecutor implements Executor {
 2         final ArrayDeque<Runnable> mTasks = new ArrayDeque<Runnable>();
 3         Runnable mActive;
 4
 5         public synchronized void execute(final Runnable r) {
 6             mTasks.offer(new Runnable() {
 7                 public void run() {
 8                     try {
 9                         r.run();
10                     } finally {
11                         scheduleNext();
12                     }
13                 }
14             });
15             if (mActive == null) {
16                 scheduleNext();
17             }
18 }
19
20         protected synchronized void scheduleNext() {
21             if ((mActive = mTasks.poll()) != null) {
22                 THREAD_POOL_EXECUTOR.execute(mActive);
23             }
24         }
25     }  

THREAD_POOL_EXECUTOR 并发线程池

asynctask.setDefaultExecutor(AsyncTask.THREAD_POOL_EXECUTOR); //设置使用 并发线程池

//params 都是使用在doInBackground(Params... params);

asynctask.executeOnExecutor(executor, params); //可以自定义 线程池     使用这两种方法