netty4 io.netty.util.IllegalReferenceCountException: refCnt: 0, decrement: 1

╰半夏微凉° 2022-05-09 04:38 246阅读 0赞

在netty4中，对象的生命周期由引用计数器控制，ByteBuf就是如此，每个对象的初始化引用计数加1，调用一次release方法，引用计数器会减1，当尝试访问计数器为0时，对象时，会抛出`IllegalReferenceCountException`，正如`ensureAccessible`的实现，更加详细的解释可以参考[官方文档][Link 1]

原因分析：日志显示refCnt=0了，表明使用的这个ByteBuf已经被回收了，代码中调用ctx.writeAndFlush(buff)会使此次ByteBuf回收也即将refCnt置为0

个人理解：ack消息代码里;

buff.release();
    
    netty提供的一个释放ByteBuf内存的方法(ReferenceCountUtil.release(msg);)，
    如果不采用这个，直接调用ByteBuf.release方法也可以，但是因为上面调用了writeAndFlush方法，
    已经将ByteBuf的refCnt置为0了，这个里面调用的时候又会在设置一次，但是发现已经为0了，
    所以就抛出的该异常。

报错信息：

io.netty.util.IllegalReferenceCountException: refCnt: 0, decrement: 1
    	at io.netty.buffer.AbstractReferenceCountedByteBuf.release(AbstractReferenceCountedByteBuf.java:101)
    	at com.alex.data.netty.utils.NettyUtil.sendMessage(NettyUtil.java:35)
    	at com.alex.data.netty.service.ServiceMessage.handlerVehLoginData(ServiceMessage.java:124)
    	at com.alex.data.netty.service.ServiceMessage.analysisVehDataByMessage(ServiceMessage.java:69)
    	at com.alex.data.netty.server.VehMessageHandler.channelRead(VehMessageHandler.java:72)
    	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:318)
    	at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:304)
    	at io.netty.handler.timeout.IdleStateHandler.channelRead(IdleStateHandler.java:266)
    	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:318)
    	at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:304)
    	at io.netty.handler.codec.ByteToMessageDecoder.fireChannelRead(ByteToMessageDecoder.java:276)
    	at io.netty.handler.codec.ByteToMessageDecoder.channelRead(ByteToMessageDecoder.java:263)
    	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:318)
    	at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:304)
    	at io.netty.channel.DefaultChannelPipeline.fireChannelRead(DefaultChannelPipeline.java:846)
    	at io.netty.channel.nio.AbstractNioByteChannel$NioByteUnsafe.read(AbstractNioByteChannel.java:131)
    	at io.netty.channel.nio.NioEventLoop.processSelectedKey(NioEventLoop.java:511)
    	at io.netty.channel.nio.NioEventLoop.processSelectedKeysOptimized(NioEventLoop.java:468)
    	at io.netty.channel.nio.NioEventLoop.processSelectedKeys(NioEventLoop.java:382)
    	at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:354)
    	at io.netty.util.concurrent.SingleThreadEventExecutor$2.run(SingleThreadEventExecutor.java:112)
    	at io.netty.util.concurrent.DefaultThreadFactory$DefaultRunnableDecorator.run(DefaultThreadFactory.java:137)
    	at java.lang.Thread.run(Thread.java:745)

ack消息的方式如下

/**
    	 * 发送消息
    	 * @param msg
    	 * @param channel
    	 */
    	public static void sendMessage(byte[] msg, Channel channel) {
    		if(channel == null) {
    			logger.error("channel == null,can't ack msg|"+ CodecUtil.byte2HexStr(msg));
    			return;
    		}
    		ByteBuf buff = channel.alloc().buffer();
    		buff.writeBytes(msg);
    		channel.writeAndFlush(buff);
    //TODO		buff.release();//此处会引起 对象的生命周期由引用计数器控制异常分析 IllegalReferenceCountException refCnt: 0, decrement: 1
    	}

[Link 1]: https://netty.io/wiki/reference-counted-objects.html