AsyncTask出现RejectExcetionExcetion原因

在项目中使用AsyncTask过程中，出现过RejectedExecutionException这个异常，经过查看源码，发现在构造ThreadPoolExecutor时，ThreadPoolExecutor内部默认的RejectedExecutionHandler是AbortPolicy来实现的，AbortPolicy见名知义就是中断执行的策略既是抛出RuntimeException。在ThreadPoolExecutor内部有多种RejectedExecutionHandler的实现，包括：

AbortPolicy： 实现rejectdException方法的就是 throw RejectedExecutionException。  这也就是android上碰到的异常。

    public static class AbortPolicy implements RejectedExecutionHandler {        /**         * Creates an {@code AbortPolicy}.         */        public AbortPolicy() { }        public void rejectedExecution(Runnable r, ThreadPoolExecutor e) {            throw new RejectedExecutionException("Task " + r.toString() +                                                 " rejected from " +                                                 e.toString());        }    }

CallerRunsPolicy：从rejectdException的实现来看，直接调用Runnable#run()方法，不会扔出异常，而是让任务继续执行。

public static class CallerRunsPolicy implements RejectedExecutionHandler {        /**         * Creates a {@code CallerRunsPolicy}.         */        public CallerRunsPolicy() { }        /**         * Executes task r in the caller's thread, unless the executor         * has been shut down, in which case the task is discarded.         *         * @param r the runnable task requested to be executed         * @param e the executor attempting to execute this task         */        public void rejectedExecution(Runnable r, ThreadPoolExecutor e) {            if (!e.isShutdown()) {                r.run();            }        }    }

DiscardPolicy：rejectdException方法是一个空的实现，意思是忽略这个任务，此任务将不被执行

/**     * A handler for rejected tasks that silently discards the     * rejected task.     */    public static class DiscardPolicy implements RejectedExecutionHandler {        /**         * Creates a {@code DiscardPolicy}.         */        public DiscardPolicy() { }        /**         * Does nothing, which has the effect of discarding task r.         *         * @param r the runnable task requested to be executed         * @param e the executor attempting to execute this task         */        public void rejectedExecution(Runnable r, ThreadPoolExecutor e) {        }    }

DiscardOldestPlicy：rejectdException方法实现了将上一个任务移除，转而执行当前最新的这个任务。

 /**     * A handler for rejected tasks that discards the oldest unhandled     * request and then retries {@code execute}, unless the executor     * is shut down, in which case the task is discarded.     */    public static class DiscardOldestPolicy implements RejectedExecutionHandler {        /**         * Creates a {@code DiscardOldestPolicy} for the given executor.         */        public DiscardOldestPolicy() { }        /**         * Obtains and ignores the next task that the executor         * would otherwise execute, if one is immediately available,         * and then retries execution of task r, unless the executor         * is shut down, in which case task r is instead discarded.         *         * @param r the runnable task requested to be executed         * @param e the executor attempting to execute this task         */        public void rejectedExecution(Runnable r, ThreadPoolExecutor e) {            if (!e.isShutdown()) {                e.getQueue().poll();                e.execute(r);            }        }    }

根据上面的这些策略，我们可以根据我们的需求来设置不同的reject策略。如果上面都不能满足我们的需求，我们可以自己实现RejectedExecutionHandler。 那么我们如何设置AsyncTask的reject策略呢？

请参考以下代码：

ThreadPoolExecutor threadPoolExecutor = (ThreadPoolExecutor) AsyncTask.THREAD_POOL_EXECUTOR;threadPoolExecutor.setRejectedExecutionHandler(new RejectedExecutionHandler() {@Overridepublic void rejectedExecution(Runnable r,ThreadPoolExecutor executor) {... //实现你的策略}});