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https://issues.apache.org/jira/browse/TINKERPOP-2005?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16555779#comment-16555779
 ] 

Dmitri Bourlatchkov commented on TINKERPOP-2005:
------------------------------------------------

The problem appears to be that if the script execution timeout happens right 
after the script produced results, while the server is sending a "successful" 
reply (see {{org.apache.tinkerpop.gremlin.server.op.AbstractOpProcessor}}, line 
194, statement: {{ctx.writeAndFlush(frame)}}), the server may also 
_asynchronously_ send a "timeout" reply.

Depending on the order of arrival of those messages, the client may receive the 
"successful" reply after it removed the corresponding entry from the "pending" 
map in {{org.apache.tinkerpop.gremlin.driver.Handler.GremlinResponseHandler}}, 
hence the NPE.

> Intermittent NullPointerException in response handling
> ------------------------------------------------------
>
>                 Key: TINKERPOP-2005
>                 URL: https://issues.apache.org/jira/browse/TINKERPOP-2005
>             Project: TinkerPop
>          Issue Type: Improvement
>          Components: driver
>    Affects Versions: 3.2.9
>            Reporter: stephen mallette
>            Priority: Minor
>
> This stacktrace was reported to me:
> {code}
> 06:11:01 2018-07-05 13:11:01,706 ERROR 13:11:01,618 Could not process the 
> response
> 06:11:01 java.lang.NullPointerException: null
> 06:11:01      at 
> org.apache.tinkerpop.gremlin.driver.Handler$GremlinResponseHandler.lambda$channelRead0$39(Handler.java:220)
> 06:11:01      at java.util.ArrayList.forEach(ArrayList.java:1257)
> 06:11:01      at 
> org.apache.tinkerpop.gremlin.driver.Handler$GremlinResponseHandler.channelRead0(Handler.java:220)
> 06:11:01      at 
> org.apache.tinkerpop.gremlin.driver.Handler$GremlinResponseHandler.channelRead0(Handler.java:197)
> 06:11:01      at 
> io.netty.channel.SimpleChannelInboundHandler.channelRead(SimpleChannelInboundHandler.java:105)
> 06:11:01      at 
> io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:362)
> 06:11:01      at 
> io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:348)
> 06:11:01      at 
> io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:340)
> 06:11:01      at 
> org.apache.tinkerpop.gremlin.driver.Handler$GremlinSaslAuthenticationHandler.channelRead0(Handler.java:123)
> 06:11:01      at 
> org.apache.tinkerpop.gremlin.driver.Handler$GremlinSaslAuthenticationHandler.channelRead0(Handler.java:67)
> 06:11:01      at 
> io.netty.channel.SimpleChannelInboundHandler.channelRead(SimpleChannelInboundHandler.java:105)
> 06:11:01      at 
> io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:362)
> 06:11:01      at 
> io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:348)
> 06:11:01      at 
> io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:340)
> 06:11:01      at 
> io.netty.handler.codec.MessageToMessageDecoder.channelRead(MessageToMessageDecoder.java:102)
> 06:11:01      at 
> io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:362)
> 06:11:01      at 
> io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:348)
> 06:11:01      at 
> io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:340)
> 06:11:01      at 
> org.apache.tinkerpop.gremlin.driver.handler.WebSocketClientHandler.channelRead0(WebSocketClientHandler.java:94)
> 06:11:01      at 
> io.netty.channel.SimpleChannelInboundHandler.channelRead(SimpleChannelInboundHandler.java:105)
> 06:11:01      at 
> io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:362)
> 06:11:01      at 
> io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:348)
> 06:11:01      at 
> io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:340)
> 06:11:01      at 
> io.netty.handler.codec.ByteToMessageDecoder.fireChannelRead(ByteToMessageDecoder.java:310)
> 06:11:01      at 
> io.netty.handler.codec.ByteToMessageDecoder.channelRead(ByteToMessageDecoder.java:284)
> 06:11:01      at 
> io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:362)
> 06:11:01      at 
> io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:348)
> 06:11:01      at 
> io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:340)
> 06:11:01      at 
> io.netty.channel.DefaultChannelPipeline$HeadContext.channelRead(DefaultChannelPipeline.java:1334)
> 06:11:01      at 
> io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:362)
> 06:11:01      at 
> io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:348)
> 06:11:01      at 
> io.netty.channel.DefaultChannelPipeline.fireChannelRead(DefaultChannelPipeline.java:926)
> 06:11:01      at 
> io.netty.channel.nio.AbstractNioByteChannel$NioByteUnsafe.read(AbstractNioByteChannel.java:134)
> 06:11:01      at 
> io.netty.channel.nio.NioEventLoop.processSelectedKey(NioEventLoop.java:644)
> 06:11:01      at 
> io.netty.channel.nio.NioEventLoop.processSelectedKeysOptimized(NioEventLoop.java:579)
> 06:11:01      at 
> io.netty.channel.nio.NioEventLoop.processSelectedKeys(NioEventLoop.java:496)
> 06:11:01      at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:458)
> 06:11:01      at 
> io.netty.util.concurrent.SingleThreadEventExecutor$5.run(SingleThreadEventExecutor.java:858)
> 06:11:01      at java.lang.Thread.run(Thread.java:748)
> {code}
> Some initial investigation seems to indicate that it is intermittent and 
> likely some form of timing issue. Will probably be hard to recreate. Hesitant 
> to just make the problem go away without understanding why it is happening. 



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