java nioÔÚ¶àÏ̻߳·¾³ÏµĶñÃÎÖ®ÖÕ½á

ÓÐÈË˵java nioÔÚ¶àÏ̻߳·¾³Ï±à³Ì¼òÖ±¾ÍÊǸö¶ñÃÎ,ÆäʵÄãÈç¹ûÄÜ°ÑÎÕסjava nio APIµÄÒªÁì,Äã¾Í¿ÉÒÔ½«Ö®¼ÝÔ¦.
0. Ò»¸ö channal ¶ÔÓ¦Ò»¸öSelectionKey in the same selector.
e.g:
SelectionKey sk=sc.register(selector, SelectionKey.OP_READ, handler);
sk==sc.register(selector, SelectionKey.OP_WRITE, handler) true?
selector.select() ÿ´Î·µ»ØµÄ¶ÔͬһchannalµÄskÊÇ·ñÏàͬ?
1.channel.register(...) may block if invoked concurrently with another registration[another.register(...)] or selection operation[selector.select(...)] involving *****the same selector*****.
Õâ¸öÊÇregister·½·¨jdk srcÉϵÄÔ­ÎÄ,
e.g:
Èç¹ûÒ»¸öselection threadÒѾ­ÔÚselect·½·¨Éϵȴýing,ÄÇôÕâ¸öʱºòÈç¹ûÓÐÁíÒ»ÌõÏ̵߳÷ÓÃchannal.register·½·¨µÄ»°,ÄÇôËü½«±»blocking.
2.selectionKey.cancel() : The key will be removed from all of the selector's key sets during *****the next selection operation[selector.select(...)]*****.
may block briefly if invoked concurrently with a cancellation[cancel()] or selection operation[select(...)] involving ***the same selector***.
Õâ¸öÒ²ÊÇcancel·½·¨jdk srcÉϵÄÔ­ÎÄ,
e.g:
ÄãÏȽ«Ò»¸öselectionKey.cancel(),È»ºóËæ¼´ÔÙchannel.register to the same selector,
ÔÚcancelºÍregisterÖ®¼ä,Èç¹ûûÓÐÏß³Ì(°üÀ¨µ±Ç°Ïß³Ì)½øÐÐselect²Ù×÷µÄ»°,
ÄÇô throws java.nio.channels.CancelledKeyException.
ËùÒÔ cancel-->select-->re-register. 
3.if don't remove the current selectedKey from selector.selectedKeys()[Set] ½«µ¼Ö selector.select(...) not block [may be cpu 100%,specially when client cut the current channel(connection)].
e.g:
Iterator<SelectionKey> it=selector.selectedKeys().iterator();
...for/while it.hasNext()...
it.remove();<------*****must do it. or Keys' Set.clear() finally;
if remove the current selectedKey from selector.selectedKeys()[Set] but don't sk.interestOps(sk.interestOps()& (~sk.readyOps()));½«µ¼Ö selector.select(...) not block [select() not block several times, or excepted exception]
4.op_write should not be registered to the selector. &nbs