Netty ByteBuf泄露定位修改。

1. ByteBuf

 

2. 问题描述

日志记录中报堆外内存溢出。

 

3. 问题定位及修改

Netty提供了ByteBuf泄露的检测机制。

JVM启动参数中添加： -Dio.netty.leakDetectionLevel=advanced ， log4j2.xml配置io.netty日志记录即可。

禁用（DISABLED） – 完全禁止泄露检测，省点消耗。
简单（SIMPLE）   – 默认等级，告诉我们取样的1%的ByteBuf是否发生了泄露，但总共一次只打印一次，看不到就没有了。 高级（ADVANCED） – 告诉我们取样的1%的ByteBuf发生泄露的地方。每种类型的泄漏（创建的地方与访问路径一致）只打印一次。对性能有影响。 偏执（PARANOID） – 跟高级选项类似，但此选项检测所有ByteBuf，而不仅仅是取样的那1%。对性能有绝大的影响。

 

检测到如下泄露点，

举例1：

 13:29:25.273 [MODBUS_MESSAGE_POOL-thread-14] [] [] [] ERROR io.netty.util.ResourceLeakDetector - LEAK: ByteBuf.release() was not called before it's garbage-collected. See http://netty.io/wiki/reference-counted-objects.html for more information.
Created at:
    io.netty.buffer.AdvancedLeakAwareByteBuf.writeBytes(AdvancedLeakAwareByteBuf.java:604)
    io.netty.buffer.AbstractByteBuf.readBytes(AbstractByteBuf.java:849)
    com.pinnet.protocol.hwmodbus.message.ModbusMessageRunnable.run(ModbusMessageRunnable.java:46)
    java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
    java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
    java.lang.Thread.run(Thread.java:748)

 可以看到readBytes()创建后，没有释放。

修改：

buffer.readBytes(4).release();

举例2：

2018-06-30 13:29:25.278 [MESSAGE_POOL-thread-14] [] [] [] ERROR io.netty.util.ResourceLeakDetector - LEAK: ByteBuf.release() was not called before it's garbage-collected. See http://netty.io/wiki/reference-counted-objects.html for more information.
    #1:
    io.netty.handler.codec.ByteToMessageDecoder.channelRead(ByteToMessageDecoder.java:273) io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:362) io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:348) io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:340) io.netty.handler.timeout.IdleStateHandler.channelRead(IdleStateHandler.java:286) io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:362) io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:348) io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:340) io.netty.handler.ssl.SslHandler.unwrap(SslHandler.java:1380) io.netty.handler.ssl.SslHandler.decodeJdkCompatible(SslHandler.java:1159) io.netty.handler.ssl.SslHandler.decode(SslHandler.java:1194) io.netty.handler.codec.ByteToMessageDecoder.decodeRemovalReentryProtection(ByteToMessageDecoder.java:489) #2: io.netty.buffer.AdvancedLeakAwareByteBuf.getUnsignedShort(AdvancedLeakAwareByteBuf.java:172) io.netty.handler.codec.LengthFieldBasedFrameDecoder.getUnadjustedFrameLength(LengthFieldBasedFrameDecoder.java:469) io.netty.handler.codec.LengthFieldBasedFrameDecoder.decode(LengthFieldBasedFrameDecoder.java:417) com.pinnet.protocol.hwmodbus.tcp.MobusLengthDecoder.decode(MobusLengthDecoder.java:32) #3: io.netty.buffer.AdvancedLeakAwareByteBuf.order(AdvancedLeakAwareByteBuf.java:70) io.netty.handler.codec.LengthFieldBasedFrameDecoder.getUnadjustedFrameLength(LengthFieldBasedFrameDecoder.java:462) io.netty.handler.codec.LengthFieldBasedFrameDecoder.decode(LengthFieldBasedFrameDecoder.java:417) com.pinnet.protocol.hwmodbus.tcp.MobusLengthDecoder.decode(MobusLengthDecoder.java:32) io.netty.handler.codec.LengthFieldBasedFrameDecoder.decode(LengthFieldBasedFrameDecoder.java:343) io.netty.handler.codec.ByteToMessageDecoder.decodeRemovalReentryProtection(ByteToMessageDecoder.java:489) io.netty.handler.codec.ByteToMessageDecoder.callDecode(ByteToMessageDecoder.java:428) io.netty.handler.codec.ByteToMessageDecoder.channelRead(ByteToMessageDecoder.java:265) #4: Hint: 'decoder' will handle the message from this point. #5: Hint: 'idleHandler' will handle the message from this point.

 

 修改：解码器中释放Bytebuf in

public class MobusLengthDecoder extends LengthFieldBasedFrameDecoder { public MobusLengthDecoder(ByteOrder byteOrder, int maxFrameLength, int lengthFieldOffset, int lengthFieldLength, int lengthAdjustment, int initialBytesToStrip, boolean failFast) { super(byteOrder, maxFrameLength, lengthFieldOffset, lengthFieldLength, lengthAdjustment, initialBytesToStrip, failFast); } @Override protected Object decode(ChannelHandlerContext ctx, io.netty.buffer.ByteBuf in) throws Exception { ByteBuf buf = (ByteBuf) super.decode(ctx, in); // LEAK: ByteBuf.release() was not called before it's garbage-collected.  in.release(); ... } }