AysncTask源码解析

AsyncTask的类图

• 其中，如果使用默认的Executor其实AsyncTask中的任务是一个一个执行的。
  其中灰色的是接口

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);
        }
    }
}

从这段代码中可以看出来。
如果使用Thread_pool_executor那么就会使用线程池来执行你的task。
注释中也有：

Order of execution

When first introduced, AsyncTasks were executed serially on a single background
thread. Starting with {android.os.Build.VERSION_CODES#DONUT}, this was changed
to a pool of threads allowing multiple tasks to operate in parallel. Starting with
android.os.Build.VERSION_CODES#HONEYCOMB, tasks are executed on a single
thread to avoid common application errors caused by parallel execution

If you truly want parallel execution, you can invoke
executeOnExecutor(java.util.concurrent.Executor, Object[])} with
THREAD_POOL_EXECUTOR

• 从类图可以看出来AsyncTask主要使用了组合的方式来使用代码。

• 理解代码的一个方式是画类图，然后找一个入口然后看下去，看他是如何调用的。