java epoll是什么，讓我們一起了解一下？

epoll是Linux內(nèi)核為處理大批量文件描述符而作了改進(jìn)的poll，是Linux下多路復(fù)用IO接口select或poll的增強(qiáng)版本，能顯著提高程序在大量并發(fā)連接中只有少量活躍的情況下的系統(tǒng)CPU利用率。

如何實(shí)現(xiàn)epoll的接口？

1、創(chuàng)建epoll句柄。

2、將被監(jiān)聽的描述符添加到epoll句柄或從epool句柄中刪除或者對監(jiān)聽事件進(jìn)行修改。

3、等待事件觸發(fā)，當(dāng)超過timeout還沒有事件觸發(fā)時，就超時。

在Java中epoll的優(yōu)點(diǎn)有哪些？

1、支持一個進(jìn)程打開大數(shù)目的socket描述符。

2、IO效率不隨FD數(shù)目增加而線性下降。

3、沒有使用mmap加速內(nèi)核與用戶空間的消息傳遞。

如何使用多路復(fù)用的服務(wù)端程序，來演示JavaAPI中提供的方法與底層epoll函數(shù)實(shí)現(xiàn)的具體關(guān)系？

首先程序運(yùn)行后服務(wù)端啟動并綁定9090端口，等待客戶端連接，讀取到客戶端消息后再直接把消息后回復(fù)給客戶端。

示例代碼如下：

import?java.io.IOException;
import?java.net.InetSocketAddress;
import?java.nio.ByteBuffer;
import?java.nio.channels.*;
import?java.util.Iterator;
import?java.util.Set;
public?class?SocketMultiplexIO?{
????private?static?Selector?selector;
????public?static?void?main(String[]?args)?throws?Exception?{
????????ServerSocketChannel?serverSocketChannel?=?ServerSocketChannel.open();
????????serverSocketChannel.bind(new?InetSocketAddress(9090));
????????serverSocketChannel.configureBlocking(false);
????????selector?=?Selector.open();
????????serverSocketChannel.register(selector,?SelectionKey.OP_ACCEPT);
????????System.out.println("服務(wù)端啟動了。。。");
????????while?(true)?{
????????????Set?keys?=?selector.keys();
????????????System.out.println("當(dāng)前epoll注冊的事件："?+?keys.size());
????????????while?(selector.select()?>?0)?{
????????????????Set?selectionKeys?=?selector.selectedKeys();
????????????????Iterator?iterator?=?selectionKeys.iterator();
????????????????while?(iterator.hasNext())?{
????????????????????SelectionKey?selectionKey?=?iterator.next();
????????????????????iterator.remove();
????????????????????if?(selectionKey.isAcceptable())?{
????????????????????????System.out.println("有一個客戶端連接了。。。");
????????????????????????acceptHandler(selectionKey);
????????????????????}?else?if?(selectionKey.isReadable())?{
????????????????????????selectionKey.cancel();
????????????????????????System.out.println("cancel函數(shù)，取消了accept事件");
????????????????????????readHandler(selectionKey);
????????????????????}
????????????????}
????????????}
????????}
????}
????private?static?void?readHandler(SelectionKey?key)?{
????????SocketChannel?client?=?(SocketChannel)?key.channel();
????????ByteBuffer?buffer?=?(ByteBuffer)?key.attachment();
????????buffer.clear();
????????int?read;
????????try?{
????????????while?(true)?{
????????????????read?=?client.read(buffer);
????????????????if?(read?>?0)?{
????????????????????buffer.flip();
????????????????????while?(buffer.hasRemaining())?{
????????????????????????client.write(buffer);
????????????????????}
????????????????????buffer.clear();
????????????????}?else?if?(read?==?0)?{
????????????????????break;
????????????????}?else?{
????????????????????client.close();
????????????????????break;
????????????????}
????????????}
????????}?catch?(IOException?e)?{
????????????e.printStackTrace();
????????}
????}
????private?static?void?acceptHandler(SelectionKey?selectionKey)?throws?IOException?{
????????ServerSocketChannel?serverSocketChannel?=?(ServerSocketChannel)?selectionKey.channel();
????????SocketChannel?accept?=?serverSocketChannel.accept();
????????accept.configureBlocking(false);
????????ByteBuffer?byteBuffer?=?ByteBuffer.allocateDirect(1024);
????????accept.register(selector,?SelectionKey.OP_READ,?byteBuffer);
????}
}

以上就是小編今天的分享了，希望可以幫助到大家。