Netty 中的 ByteBuffers 导致内存泄漏

Question

我创建了一个小型 Netty 服务器来计算 BigInteger 的阶乘并发送结果。代码如下

Factorial.java

public class Factorial {

    private int port;

    public Factorial(int port) {
        this.port = port;
    }

    public void run(int threadcount) throws Exception {
        EventLoopGroup bossGroup = new NioEventLoopGroup();
        EventLoopGroup workerGroup = new NioEventLoopGroup(threadcount);
        try {
            ServerBootstrap b = new ServerBootstrap();
            b.group(bossGroup, workerGroup)
             .channel(NioServerSocketChannel.class)
             .childHandler(new ChannelInitializer<SocketChannel>() {
                 @Override
                 public void initChannel(SocketChannel ch) throws Exception {
                     ch.pipeline().addLast(new FactorialHandler());
                 }
             })
             .option(ChannelOption.SO_BACKLOG, 128)          
             .childOption(ChannelOption.SO_KEEPALIVE, true); 

            ChannelFuture f = b.bind(port).sync(); 

            f.channel().closeFuture().sync();
        } finally {
            workerGroup.shutdownGracefully();
            bossGroup.shutdownGracefully();
        }
    }

    public static void main(String[] args) throws Exception {
        int port = 15000;
        new Factorial(port).run(Integer.parseInt(args[0]));
    }
}

FactorialHandler.java

public class FactorialHandler extends ChannelInboundHandlerAdapter {

    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) { 
        BigInteger result = BigInteger.ONE;
        String resultString;
        for (int i=2000; i>0; i--)
            result = result.multiply(BigInteger.valueOf(i));
        resultString = result.toString().substring(0, 3)+"\n";
        ByteBuf buf = Unpooled.copiedBuffer(resultString.getBytes());
        ctx.write(buf);
        ctx.flush();
    }

    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) {
        cause.printStackTrace();
        ctx.close();
    }
}

当我运行这个我得到了以下错误

Jun 08, 2018 5:28:09 PM io.netty.util.ResourceLeakDetector reportTracedLeak
SEVERE: LEAK: ByteBuf.release() was not called before it's garbage-collected. See http://netty.io/wiki/reference-counted-objects.html for more information.
Recent access records:

正如给定的link中所解释的，我在ctx.flush()之后的channelRead方法中调用buf.release()释放了ByteBuffer。

但是当我这样做时，服务器开始抛出以下异常

io.netty.util.IllegalReferenceCountException: refCnt: 0, increment: 1

有人可以告诉我如何解决这个问题吗？

Answer 1

因为你没有调用msg.release()（msg是ByteBuf的一个实例）

Answer 2

问题不在于出站 ByteBuf。 Outbound ByteBufs 总是为你处理（参见 OutboundMessages). The problem is the inbound ByteBuf. I'm looking at you, FactorialHandler. It extends ChannelInboundHandlerAdapter。注意 JavaDoc 中的这一点：

Be aware that messages are not released after the channelRead(ChannelHandlerContext, Object) method returns automatically. If you are looking for a ChannelInboundHandler implementation that releases the received messages automatically, please see SimpleChannelInboundHandler.

您的处理程序具有如下签名：

public void channelRead(ChannelHandlerContext ctx, Object msg)

那个 msg，（顺便说一句，你不使用它）实际上是一个 ByteBuf，这正是上面的 JavaDoc 注释警告你的内容。（在没有任何其他 ChannelHandler 的情况下，消息将始终是 ByteBuf 的实例。）

所以你的选择是：

使用 SimpleChannelInboundHandler 将为您清理该引用。
在处理程序结束时，使用 ReferenceCountUtil.release(java.lang.Object msg) 释放入站 ByteBuf。

Netty 中的 ByteBuffers 导致内存泄漏

Memory leak due to ByteBuffers in Netty

java

netty