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netty中epoll server和nio server的使用

netty中epoll server和nio server的使用


這幾天有空研究了下netty中的EpollEventLoopGroupNioEventLoopGroup的用法,在編碼上沒有顯著的不同,對應的epoll,有一套的api供於使用,但是因為只能在linux機上使用,因此又藉助了docker執行linux容器來執行相應程式,這節就來具體的講述下。

nio server


編寫了一個簡單的Hello world的http server,不講述詳細程式碼了,只講下最後的server中的部分原始碼,我採用的netty的版本是netty 4.0的,在這就不再使用netty5了,netty5因為一些更為複雜的特性和沒有顯著的提高效能已經被放棄了,這裡就不再提了。

HttpHelloWorldServerHandler:

package cn.com.epoll;

import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelFutureListener;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInboundHandlerAdapter;
import io.netty.handler.codec.http.*;
import io.netty.util.AsciiString;

/**
 * Created by xiaxuan on 17/11/14.
 */
public class HttpHelloWorldServerHandler extends ChannelInboundHandlerAdapter { private static final byte[] CONTENT = { 'H', 'e', 'l', 'l', 'o', ' ', 'W', 'o', 'r', 'l', 'd'}; private static final AsciiString CONTENT_TYPE = new AsciiString("Content-Type"); private static final AsciiString CONTENT_LENGTH = new
AsciiString("Content-Length"); private static final AsciiString CONNECTION = new AsciiString("Connection"); private static final AsciiString KEEP_ALIVE = new AsciiString("keep-alive"); @Override public void channelReadComplete(ChannelHandlerContext ctx) throws Exception { ctx.flush(); } @Override public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception { if (msg instanceof HttpRequest) { HttpRequest req = (HttpRequest) msg; if (HttpUtil.is100ContinueExpected(req)) { ctx.write(new DefaultFullHttpResponse(HttpVersion.HTTP_1_1, HttpResponseStatus.CONTINUE)); } boolean keepAlive = HttpUtil.isKeepAlive(req); FullHttpResponse response = new DefaultFullHttpResponse(HttpVersion.HTTP_1_1, HttpResponseStatus.OK, Unpooled.wrappedBuffer(CONTENT)); response.headers().set(CONTENT_TYPE, "text/plain"); response.headers().set(CONTENT_LENGTH, response.content().readableBytes()); if (!keepAlive) { ctx.write(response).addListener(ChannelFutureListener.CLOSE); } else { response.headers().set(CONNECTION, KEEP_ALIVE); ctx.write(response); } } } @Override public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception { cause.printStackTrace(); ctx.close(); } }

channelRead的方法很簡單,就是判斷當前是不是http請求,是的話就輸出Hello World,功能比較簡單。

HttpHelloWorldServerInitializer:

public class HttpHelloWorldServerInitializer extends ChannelInitializer<SocketChannel> {
    @Override
    protected void initChannel(SocketChannel ch) throws Exception {
        ch.pipeline().addLast(new HttpServerCodec());
        ch.pipeline().addLast(new HttpHelloWorldServerHandler());
    }
}

pipline新增Handler處理。

NioHttpHelloWorldServer:

package cn.com.epoll;

import io.netty.bootstrap.ServerBootstrap;
import io.netty.buffer.PooledByteBufAllocator;
import io.netty.channel.Channel;
import io.netty.channel.ChannelOption;
import io.netty.channel.EventLoopGroup;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.nio.NioServerSocketChannel;

/**
 * Created by xiaxuan on 17/11/14.
 */
public class NioHttpHelloWorldServer {

    private static final int PORT = Integer.parseInt(System.getProperty("port", "8080"));

    public static void main(String[] args) {
        EventLoopGroup bossGroup = new NioEventLoopGroup(1);
        EventLoopGroup workerGroup = new NioEventLoopGroup();
        ServerBootstrap b = new ServerBootstrap();
        try {
            b.group(bossGroup, workerGroup)
                    .channel(NioServerSocketChannel.class)
                    .option(ChannelOption.SO_BACKLOG, 1024)
                    .childOption(ChannelOption.ALLOCATOR, PooledByteBufAllocator.DEFAULT)
                    .childHandler(new HttpHelloWorldServerInitializer());

            Channel ch = b.bind(PORT).channel();
            ch.closeFuture().sync();
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            bossGroup.shutdownGracefully();
            workerGroup.shutdownGracefully();
        }

    }
}

普通的netty演示程式的寫法,沒什麼特殊的,但是還是需要提一下其中使用的NioEventLoopGroup,NioEventLoopGroup就是一個簡單的執行緒池排程服務,我們再追溯NioEventLoopGroup的原始碼的時候可以發現最終NioEventLoopGroup繼承的就是ScheduledExecutorService,就是有多個NioEventLoop物件的執行緒池,如果不指定執行緒池的的容量的話,預設就是當前cpu * 2的數量,轉到原始碼可以看到傳入的建構函式為0,為以下:

 * Create a new instance using the default number of threads, the default {@link ThreadFactory} and
     * the {@link SelectorProvider} which is returned by {@link SelectorProvider#provider()}.
     */
    public NioEventLoopGroup() {
        this(0);
    }

但是轉到最終原始碼會發現當判斷為0的時候,去了預設值,原始碼如下:

 static {
        DEFAULT_EVENT_LOOP_THREADS = Math.max(1, SystemPropertyUtil.getInt(
                "io.netty.eventLoopThreads", NettyRuntime.availableProcessors() * 2));

        if (logger.isDebugEnabled()) {
            logger.debug("-Dio.netty.eventLoopThreads: {}", DEFAULT_EVENT_LOOP_THREADS);
        }
    }

    /**
     * @see MultithreadEventExecutorGroup#MultithreadEventExecutorGroup(int, Executor, Object...)
     */
    protected MultithreadEventLoopGroup(int nThreads, Executor executor, Object... args) {
        super(nThreads == 0 ? DEFAULT_EVENT_LOOP_THREADS : nThreads, executor, args);
    }

如上,最終取得預設值就是cpu * 2。

而這裡最終還是需要提一下NioEventLoop,NioEventLoop的父類繼承了SingleThreadEventExecutor,也是一個執行緒池排程服務,但是隻有一個單執行緒,在NioEventLoop建立的時候,同時也會建立一個Selector,selector管理channel,所以實際上NioEventLoopGroup就是一組管理Channel的執行緒池。

原始碼解析就到此未知,執行程式,在web端請求的效果如下:

十分簡單,這是nio server的執行。

epoll server


epoll server的原始碼主要在server上的不同,其他的與上相同,server如下:

package cn.com.epoll;

import io.netty.bootstrap.ServerBootstrap;
import io.netty.buffer.PooledByteBufAllocator;
import io.netty.channel.Channel;
import io.netty.channel.ChannelOption;
import io.netty.channel.EventLoopGroup;
import io.netty.channel.epoll.EpollEventLoopGroup;
import io.netty.channel.epoll.EpollServerSocketChannel;

/**
 * Created by xiaxuan on 17/11/14.
 */
public class HttpHelloWorldServer {

    static final int PORT = Integer.parseInt(System.getProperty("port", "8080"));

    public static void main(String[] args) {
        EventLoopGroup bossGroup = new EpollEventLoopGroup(1);
        EventLoopGroup workerGroup = new EpollEventLoopGroup();

        try {
            ServerBootstrap b = new ServerBootstrap();
            b.channel(EpollServerSocketChannel.class);
            b.option(ChannelOption.SO_BACKLOG, 1024);
            b.childOption(ChannelOption.ALLOCATOR, PooledByteBufAllocator.DEFAULT);
            b.group(bossGroup, workerGroup)
                    .childHandler(new HttpHelloWorldServerInitializer());
            Channel ch = b.bind(PORT).sync().channel();
            ch.closeFuture().sync();
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            bossGroup.shutdownGracefully();
            workerGroup.shutdownGracefully();
        }
    }
}

暫時先不講Epoll和nio selector特性的不同,首先先把這裡的應用程式講完,在普通的windows或者mac上運行當前的程式會執行不起來的,會報錯為:

Exception in thread "main" java.lang.UnsatisfiedLinkError: failed to load the required native library
    at io.netty.channel.epoll.Epoll.ensureAvailability(Epoll.java:78)
    at io.netty.channel.epoll.EpollEventLoopGroup.<clinit>(EpollEventLoopGroup.java:38)
    at cn.com.epoll.HttpHelloWorldServer.main(HttpHelloWorldServer.java:19)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:483)
    at com.intellij.rt.execution.application.AppMain.main(AppMain.java:147)
Caused by: java.lang.ExceptionInInitializerError
    at io.netty.channel.epoll.Epoll.<clinit>(Epoll.java:33)
    ... 7 more
Caused by: java.lang.IllegalStateException: Only supported on Linux
    at io.netty.channel.epoll.Native.loadNativeLibrary(Native.java:189)
    at io.netty.channel.epoll.Native.<clinit>(Native.java:61)
    ... 8 more

epoll模型只有在linux kernel 2.6以上才能支援,在windows和mac都是不支援的,因此需要在linux上執行這個程式,但是本機是mac系統,因此不能在本地執行,然後本地也沒有安裝linux虛擬機器,因此便藉助了docker來使程式執行,於此同時為了方便執行maven打出的jar包,藉助了一個maven外掛以供打出一個可執行的jar包,外掛如下:

<plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-shade-plugin</artifactId>
                <version>2.3</version>
                <executions>
                    <execution>
                        <phase>package</phase>
                        <goals>
                            <goal>shade</goal>
                        </goals>
                        <configuration>
                            <transformers>
                                <transformer implementation="org.apache.maven.plugins.shade.resource.ManifestResourceTransformer">
                                    <mainClass>${exec.mainClass}</mainClass>
                                </transformer>
                            </transformers>
                            <artifactSet>
                            </artifactSet>
                        </configuration>
                    </execution>
                </executions>
            </plugin>

然後編寫的Dockerfile檔案如下:

FROM java:8
MAINTAINER bingwenwuhen bingwenwuhen@163.com

RUN mkdir /app
COPY target/epoll-server-1.0-SNAPSHOT.jar /app

ENTRYPOINT ["java", "-jar", "app/epoll-server-1.0-SNAPSHOT.jar"]
EXPOSE 8080

我拉取的這個java:8基礎映象就是以centos為基礎映象,因此就是linux環境,在可能一些基礎映象上並非支援epoll模型的可能性上,可以直接拉取centos映象,然後配置java環境等等,在此不再詳述,這個在網上有著足夠的資料。

在maven編譯打包之後,docker進行映象構建,執行,最後執行docker ps命令,檢視容器執行情況,如下:

容器正常執行,使用curl命令請求服務,將會獲取如上一樣的結果,epoll server正常執行。

我們在檢視EpollEventLoopGroup原始碼的時候可以發現,NioEventLoopGroup和EpollEventgroup最終繼承的類都是相同,只是部分特性不同而已,因此在這就不再講述EpollEventLoopGroup的原始碼,然而epoll模型本身講述起來又相當複雜,不是本節能夠講述清楚的,對於EpollEventLoopGroup與epoll模型,以後有空再做專題詳述。

原始碼下載地址


NioEventLoopGroup的原始碼下載地址就不再給出,下面是epoll server的原始碼下載地址:

原始碼下載地址