private Runnable poll() {
            synchronized (mPool) {
                try {
                    return mPool.poll();
                } catch (NoSuchElementException e) {
                    e.printStackTrace();
                    return null;
                }
            }
        }
poll a Runnable form {@link #mPool}

@return Runnable
caprice/kit-handler/src/main/java/net/qiujuer/genius/kit/handler/HandlerPoster.java