android AsyncTask 源码跟踪

android 处理异：AsyncTask

new MyAysnTask("AysnTask-1").execute("");

如何实现的就不写了，自行百度，下面来看一下execute方法：

    @MainThread    public final AsyncTask execute(Params... params) {        return executeOnExecutor(sDefaultExecutor, params);    }

可见execute里面又调用了executeOnExecutor()，这个是方法是通过一个线程池来执行，sDefaultExecutor是AsyncTask一个默认的线程池：串行线程池类

    private static final int CPU_COUNT =     Runtime.getRuntime().availableProcessors();    //至少2个线程和最多4个线程在核心池中    // We want at least 2 threads and at most 4 threads in the core pool,    // preferring to have 1 less than the CPU count to avoid saturating    // the CPU with background work    private static final int CORE_POOL_SIZE = Math.max(2,     Math.min(CPU_COUNT - 1, 4));    private static final int MAXIMUM_POOL_SIZE = CPU_COUNT * 2 + 1;    private static final int KEEP_ALIVE_SECONDS = 30;    static {        ThreadPoolExecutor threadPoolExecutor = new ThreadPoolExecutor(                CORE_POOL_SIZE, MAXIMUM_POOL_SIZE, KEEP_ALIVE_SECONDS, TimeUnit.SECONDS,                sPoolWorkQueue, sThreadFactory);        threadPoolExecutor.allowCoreThreadTimeOut(true);        THREAD_POOL_EXECUTOR = threadPoolExecutor;//默认线程池    }private static volatile Executor sDefaultExecutor = SERIAL_EXECUTOR;public static final Executor SERIAL_EXECUTOR = new SerialExecutor();    private static class SerialExecutor implements Executor {        final ArrayDeque mTasks = new ArrayDeque();        Runnable mActive;        public synchronized void execute(final Runnable r) {          // mTasks.offer(E e) 在队列尾部添加一个元素，并返回是否成功         mTasks.offer(new Runnable() {                public void run() {                    try {                      //等待执行                        r.run();                    } finally {                        //执行下一个调度线程，这样在一个队列中就实现了串行调度                        scheduleNext();                    }                }            });           //首次执行            if (mActive == null) {                scheduleNext();            }        }        protected synchronized void scheduleNext() {        //poll()  删除队列中第一个元素，并返回该元素的值,如果元素为null，        //将返回null(其实调用的是pollFirst())            if ((mActive = mTasks.poll()) != null) {              //取一个任务。不为空就执行。                THREAD_POOL_EXECUTOR.execute(mActive);            }        }    }

那么executeOnExecutor方法如下：

   @MainThread    public final AsyncTask         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);        return this;    }

没完。。。。。。。。。。。。。。。。

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