I’m currently developing a java package similar to .net signalr that utilizes netty. As I tried to benchmark it I realized that there’s a memory leak in my application. I narrowed down my search to the section where I write the result of the client request back to the TCP channel. Code below is where the memory leak is happening.

private ChannelFuture writeMessageInternal(Message message) {
        ByteBuf buf;
        Codec codec = message.getCodec();
        try {
            buf = codec.encode(message);
        } catch (Exception e) {
            throw new RuntimeException();
        }
        ChannelFuture channelFuture = channel.writeAndFlush(buf);
        return channelFuture;
    }

If I comment ChannelFuture channelFuture = channel.writeAndFlush(buf); and change the code like:

private ChannelFuture writeMessageInternal(Message message) {
        ByteBuf buf;
        Codec codec = message.getCodec();
        try {
            buf = codec.encode(message);
        } catch (Exception e) {
            throw new RuntimeException();
        }
        // ChannelFuture channelFuture = channel.writeAndFlush(buf);
        return null;
    }

then no memory leak happens. buf is an unpooled bytebuf. So it didn’t require to be released manually.

Currently java 21 and netty-all of version 4.1.58.Final is benig used.