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fix error link. #9

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fix error link. #9

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8 changes: 4 additions & 4 deletions docs/java/java-concurrent.md
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Expand Up @@ -1226,6 +1226,10 @@ Future接口主要包括5个方法：
4. isDone()方法判断当前方法是否完成
5. isCancel()方法判断当前方法是否取消

> 参考链接：https://blog.csdn.net/u014209205/article/details/80598209

![](http://img.topjavaer.cn/img/20220612101342.png)

## select、poll、epoll之间的区别

select，poll，epoll都是IO多路复用的机制。I/O多路复用就通过一种机制，可以监视多个描述符，一旦某个描述符就绪（一般是读就绪或者写就绪），能够通知程序进行相应的读写操作。但select，poll，epoll本质上都是同步I/O，因为他们都需要在读写事件就绪后自己负责进行读写，也就是说这个读写过程是阻塞的，而异步I/O则无需自己负责进行读写，异步I/O的实现会负责把数据从内核拷贝到用户空间。
Expand All @@ -1235,7 +1239,3 @@ select的时间复杂度O(n)。它仅仅知道有I/O事件发生了，却并不
poll的时间复杂度O(n)。poll本质上和select没有区别，它将用户传入的数组拷贝到内核空间，然后查询每个fd对应的设备状态， 但是它没有最大连接数的限制，原因是它是基于链表来存储的.

epoll的时间复杂度O(1)。epoll可以理解为event poll，不同于忙轮询和无差别轮询，epoll会把哪个流发生了怎样的I/O事件通知我们。所以我们说epoll实际上是事件驱动的。

> 参考链接：https://blog.csdn.net/u014209205/article/details/80598209

![](http://img.topjavaer.cn/img/20220612101342.png)