Usage of Async DNSResolver

[etienne....@gmail.com]

Hi,

I am trying to use the netty DnsNameResolver . I correctly achieved to use it with Future in the "sync way" (get / getNow method).
I am now trying to have it work in the "callback method". In order to do so, I added a specific promise which will add a listener . Example of code is here : https://gist.github.com/etiennecarriere/cec6b37dec05a1b5301d59ec190c456a
Currently, I have a NPE on internal netty class :
java.lang.NullPointerException
    at io.netty.util.concurrent.DefaultPromise.notifyListeners(DefaultPromise.java:414) ~[netty-all-4.1.14.Final.jar:4.1.14.Final]
    at io.netty.util.concurrent.DefaultPromise.trySuccess(DefaultPromise.java:104) ~[netty-all-4.1.14.Final.jar:4.1.14.Final]
    at io.netty.resolver.dns.DnsQueryContext.setSuccess(DnsQueryContext.java:197) ~[netty-all-4.1.14.Final.jar:4.1.14.Final]
    at io.netty.resolver.dns.DnsQueryContext.finish(DnsQueryContext.java:180) ~[netty-all-4.1.14.Final.jar:4.1.14.Final]
    at io.netty.resolver.dns.DnsNameResolver$DnsResponseHandler.channelRead(DnsNameResolver.java:947) ~[netty-all-4.1.14.Final.jar:4.1.14.Final]
    at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:362) [netty-all-4.1.14.Final.jar:4.1.14.Final]
    at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:348) [netty-all-4.1.14.Final.jar:4.1.14.Final]
    at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:340) [netty-all-4.1.14.Final.jar:4.1.14.Final]
    at io.netty.handler.codec.MessageToMessageDecoder.channelRead(MessageToMessageDecoder.java:102) [netty-all-4.1.14.Final.jar:4.1.14.Final]
    at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:362) [netty-all-4.1.14.Final.jar:4.1.14.Final]
    at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:348) [netty-all-4.1.14.Final.jar:4.1.14.Final]
    at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:340) [netty-all-4.1.14.Final.jar:4.1.14.Final]
    at io.netty.channel.DefaultChannelPipeline$HeadContext.channelRead(DefaultChannelPipeline.java:1342) [netty-all-4.1.14.Final.jar:4.1.14.Final]
    at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:362) [netty-all-4.1.14.Final.jar:4.1.14.Final]
    at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:348) [netty-all-4.1.14.Final.jar:4.1.14.Final]
    at io.netty.channel.DefaultChannelPipeline.fireChannelRead(DefaultChannelPipeline.java:934) [netty-all-4.1.14.Final.jar:4.1.14.Final]
    at io.netty.channel.nio.AbstractNioMessageChannel$NioMessageUnsafe.read(AbstractNioMessageChannel.java:93) [netty-all-4.1.14.Final.jar:4.1.14.Final]
    at io.netty.channel.nio.NioEventLoop.processSelectedKey(NioEventLoop.java:645) [netty-all-4.1.14.Final.jar:4.1.14.Final]
    at io.netty.channel.nio.NioEventLoop.processSelectedKeysOptimized(NioEventLoop.java:580) [netty-all-4.1.14.Final.jar:4.1.14.Final]
    at io.netty.channel.nio.NioEventLoop.processSelectedKeys(NioEventLoop.java:497) [netty-all-4.1.14.Final.jar:4.1.14.Final]
    at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:459) [netty-all-4.1.14.Final.jar:4.1.14.Final]
    at io.netty.util.concurrent.SingleThreadEventExecutor$5.run(SingleThreadEventExecutor.java:858) [netty-all-4.1.14.Final.jar:4.1.14.Final]
    at io.netty.util.concurrent.DefaultThreadFactory$DefaultRunnableDecorator.run(DefaultThreadFactory.java:138) [netty-all-4.1.14.Final.jar:4.1.14.Final]
    at java.lang.Thread.run(Thread.java:748) [?:1.8.0_131]

When put the code in debug, I see no missing/null attribute to DnsNameResolver. 

Thank you for your help,

Regards,

Etienne Carrière

[Norman Maurer]

Thats because you not specify the EventExecutor for the Promise. 

That said I am not sure why you not just add the listener to the returned Future ?

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