内存泄漏检测要点

• 默认级别是 SIMPLE，意味着不是每次都检测；
• GC 后，才有可能检测到；
• 注意日志的级别，ERROR；
• 上线前用最高级别，上线后用默认级别；

开启内存泄漏检测

• -Dio.netty.leakDetection.level=PAPANOID；

测试步骤

• 创建一个 ByteBuf 对象不 release()；
• 客户端频繁的发消息，用于触发 GC；
• 日志级别改成 error；
• -Dio.netty.leakDetection.level=PAPANOID；

检测到内存泄露的输出

• 会有指出发生内存泄漏的位置：io.netty.example.study.server.codec.handler.OrderServerProcessHandler.channelRead0(OrderServerProcessHandler.java:25)

19:23:44 [worker-3-1] ResourceLeakDetector: LEAK: ByteBuf.release() was not called before it's garbage-collected. See https://netty.io/wiki/reference-counted-objects.html for more information.
Recent access records: 
Created at:
    io.netty.buffer.PooledByteBufAllocator.newDirectBuffer(PooledByteBufAllocator.java:349)
    io.netty.buffer.AbstractByteBufAllocator.directBuffer(AbstractByteBufAllocator.java:187)
    io.netty.buffer.AbstractByteBufAllocator.directBuffer(AbstractByteBufAllocator.java:173)
    io.netty.buffer.AbstractByteBufAllocator.buffer(AbstractByteBufAllocator.java:107)
    io.netty.example.study.server.codec.handler.OrderServerProcessHandler.channelRead0(OrderServerProcessHandler.java:25)
    io.netty.example.study.server.codec.handler.OrderServerProcessHandler.channelRead0(OrderServerProcessHandler.java:17)
    io.netty.channel.SimpleChannelInboundHandler.channelRead(SimpleChannelInboundHandler.java:105)
    io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:374)
    io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:360)
    io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:352)
    io.netty.handler.logging.LoggingHandler.channelRead(LoggingHandler.java:241)
    io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:374)
    io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:360)
    io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:352)
    io.netty.handler.codec.MessageToMessageDecoder.channelRead(MessageToMessageDecoder.java:102)
    io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:374)
    io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:360)
    io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:352)
    io.netty.handler.codec.ByteToMessageDecoder.fireChannelRead(ByteToMessageDecoder.java:328)
    io.netty.handler.codec.ByteToMessageDecoder.fireChannelRead(ByteToMessageDecoder.java:315)
    io.netty.handler.codec.ByteToMessageDecoder.callDecode(ByteToMessageDecoder.java:429)
    io.netty.handler.codec.ByteToMessageDecoder.channelRead(ByteToMessageDecoder.java:283)
    io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:374)
    io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:360)
    io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:352)
    io.netty.handler.logging.LoggingHandler.channelRead(LoggingHandler.java:241)
    io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:374)
    io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:360)
    io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:352)
    io.netty.channel.DefaultChannelPipeline$HeadContext.channelRead(DefaultChannelPipeline.java:1421)
    io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:374)
    io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:360)
    io.netty.channel.DefaultChannelPipeline.fireChannelRead(DefaultChannelPipeline.java:930)
    io.netty.channel.nio.AbstractNioByteChannel$NioByteUnsafe.read(AbstractNioByteChannel.java:163)
    io.netty.channel.nio.NioEventLoop.processSelectedKey(NioEventLoop.java:697)
    io.netty.channel.nio.NioEventLoop.processSelectedKeysOptimized(NioEventLoop.java:632)
    io.netty.channel.nio.NioEventLoop.processSelectedKeys(NioEventLoop.java:549)
    io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:511)
    io.netty.util.concurrent.SingleThreadEventExecutor$5.run(SingleThreadEventExecutor.java:918)
    io.netty.util.internal.ThreadExecutorMap$2.run(ThreadExecutorMap.java:74)
    io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30)
    java.lang.Thread.run(Thread.java:748)