android AsyncTask的局限性 及 源碼分析

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參考: http://blog.csdn.net/hitlion2008/article/details/7983449

2.3之前 AsyncTask有個全域的線程池  最大的值是5 超過後只能等待執行

3.0後增加了excuteOnExcutor方法 設定自訂線程池.但是預設線程池是個順序線程池每次只能執行一個任務且按照順序.

 

AsyncTask 部分原始碼 .

public abstract class AsyncTask<Params, Progress, Result> {    private static final String LOG_TAG = "AsyncTask";    private static final int CPU_COUNT = Runtime.getRuntime().availableProcessors();    private static final int CORE_POOL_SIZE = CPU_COUNT + 1;    private static final int MAXIMUM_POOL_SIZE = CPU_COUNT * 2 + 1;    private static final int KEEP_ALIVE = 1;    private static final ThreadFactory sThreadFactory = new ThreadFactory() {        private final AtomicInteger mCount = new AtomicInteger(1);        public Thread newThread(Runnable r) {            return new Thread(r, "AsyncTask #" + mCount.getAndIncrement());        }    };    private static final BlockingQueue<Runnable> sPoolWorkQueue =            new LinkedBlockingQueue<Runnable>(128);    /**     * An {@link Executor} that can be used to execute tasks in parallel.     */    public static final Executor THREAD_POOL_EXECUTOR            = new ThreadPoolExecutor(CORE_POOL_SIZE, MAXIMUM_POOL_SIZE, KEEP_ALIVE,                    TimeUnit.SECONDS, sPoolWorkQueue, sThreadFactory);    /**     * An {@link Executor} that executes tasks one at a time in serial     * order.  This serialization is global to a particular process.     */    public static final Executor SERIAL_EXECUTOR = new SerialExecutor();    private static final int MESSAGE_POST_RESULT = 0x1;    private static final int MESSAGE_POST_PROGRESS = 0x2;    private static final InternalHandler sHandler = new InternalHandler();    private static volatile Executor sDefaultExecutor = SERIAL_EXECUTOR;    private final WorkerRunnable<Params, Result> mWorker;    private final FutureTask<Result> mFuture;    private volatile Status mStatus = Status.PENDING;        private final AtomicBoolean mCancelled = new AtomicBoolean();    private final AtomicBoolean mTaskInvoked = new AtomicBoolean();    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);            }        }    }    /**     * Indicates the current status of the task. Each status will be set only once     * during the lifetime of a task.     */    public enum Status {        /**         * Indicates that the task has not been executed yet.         */        PENDING,        /**         * Indicates that the task is running.         */        RUNNING,        /**         * Indicates that {@link AsyncTask#onPostExecute} has finished.         */        FINISHED,    }    /** @hide Used to force static handler to be created. */    public static void init() {        sHandler.getLooper();    }    /** @hide */    public static void setDefaultExecutor(Executor exec) {        sDefaultExecutor = exec;    }    /**     * Creates a new asynchronous task. This constructor must be invoked on the UI thread.     */    public AsyncTask() {        mWorker = new WorkerRunnable<Params, Result>() {            public Result call() throws Exception {                mTaskInvoked.set(true);                Process.setThreadPriority(Process.THREAD_PRIORITY_BACKGROUND);                //noinspection unchecked                return postResult(doInBackground(mParams));            }        };        mFuture = new FutureTask<Result>(mWorker) {            @Override            protected void done() {                try {                    postResultIfNotInvoked(get());                } catch (InterruptedException e) {                    android.util.Log.w(LOG_TAG, e);                } catch (ExecutionException e) {                    throw new RuntimeException("An error occured while executing doInBackground()",                            e.getCause());                } catch (CancellationException e) {                    postResultIfNotInvoked(null);                }            }        };    }

　　查看 THREAD_POOL_EXECUTOR 幾個參數的預設設定

    private static final int CPU_COUNT = Runtime.getRuntime().availableProcessors();    private static final int CORE_POOL_SIZE = CPU_COUNT + 1;    private static final int MAXIMUM_POOL_SIZE = CPU_COUNT * 2 + 1;    private static final int KEEP_ALIVE = 1;

　　core size:cpucount+1

　　max size :cupcount*2 +1

　　alivetime:1秒

 

android AsyncTask的局限性 及 源碼分析