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From Stefan Richter <s.rich...@data-artisans.com>
Subject Re: [BUG?] Cannot Load User Class on Local Environment
Date Wed, 26 Apr 2017 14:03:28 GMT
Ok, now the question is also about what classloaders Ignite is creating and how they are used,
but the relevant code line in Flink is probably in FlinkMiniCluster.scala, line 538 (current

 try {
} finally {
   if(!useSingleActorSystem) {
     // we have to shutdown the just created actor system

This is what is executed as part of executing a job through LocalEnvironment. As we can see,
the classloader is set to the classloader of FlinkMiniCluster. Depending on the classloader
structure inside Ignite, this classloader might not know your user code. What you could do
is changing this line in a custom Flink build, changing line 538 for example to Thread.currentThread().getContextClassloader()
and ensuring that the context classloader ins the runnable is a classloader that a) knows
the user code and b) is a child of the classloader that knows the Ignite and Flink classes.
Notice that this is not a general solution and should not become a general fix.

I have heard that Till is about to change some things about local execution, so I included
him in CC. Maybe he can provide additional hints how your use case might be better supported
in the upcoming Flink 1.3.


> Am 25.04.2017 um 22:50 schrieb Matt <dromitlabs@gmail.com>:
> I updated the code a little bit for clarity, now the line #56 mentioned in my previous
message is line #25.
> In summary the error I'm getting is this:
> ---
> Caused by: org.apache.flink.streaming.runtime.tasks.StreamTaskException: Cannot load
user class: com.test.Test
> ClassLoader info: URL ClassLoader:
> Class not resolvable through given classloader.
> ---
> But if I'm not wrong, after trying to load the class through URLClassLoader, Flink should
try loading it with its parent ClassLoader, which should be the same ClassLoader that executed
the environment, and it does have access to the class.
> Not sure what is wrong.
> On Tue, Apr 25, 2017 at 5:38 PM, Matt <dromitlabs@gmail.com <mailto:dromitlabs@gmail.com>>
> Hi Stefan,
> Check the code here: https://gist.github.com/17d82ee7dd921a0d649574a361cc017d <https://gist.github.com/17d82ee7dd921a0d649574a361cc017d>
, the output is at the bottom of the page.
> Here are the results of the additional tests you mentioned:
> 1. I was able to instantiate an inner class (Test$Foo) inside the Ignite closure, no
problem with that
> 2. I tried implementing SourceFunction and SinkFunction in Test itself, I was able to
instantiate the class inside the Ignite closure
> 3. I'm not sure what you meant in this point, is it something like what I tried in line
> Additionally, I tried implementing the SourceFunction and SinkFunction in Test$Foo with
the same result: it says "Cannot load user class: com.test.Test$Foo"
> Looks like Flink is not using the correct ClassLoader. Any idea?
> Regards,
> Matt
> On Tue, Apr 25, 2017 at 7:00 AM, Stefan Richter <s.richter@data-artisans.com <mailto:s.richter@data-artisans.com>>
> Hi,
> I would expect that the local environment picks up the class path from the code that
launched it. So I think the question is what happens behind the scenes when you call ignite.compute().broadcast(runnable);
. Which classes are shipped and how is the classpath build in the environment that runs the
code. Your example is also not fully conclusive, because com.myproj.Test (which you can successfully
instantiate) and com.myproj.Test$1$2 (which fails) are different classes, so maybe only the
outer class is shipped with the broadcast call. My theory is that not all classes are shipped
(e.g. inner classes), but only Test . You could try three things to analyze to problem a little
> 1) Create another inner class inside Test and try if you are still able to instantiate
also this class via reflection.
> 2) Let Test class itself implement the map function (avoiding the usage of other/inner
classes) and see if this works.
> 3) Check and set the thread’s context classloader inside the runnable to something
that contains all required classes and see if this gets picked up by Flink.
> Best,
> Stefan
>> Am 25.04.2017 um 07:27 schrieb Matt <dromitlabs@gmail.com <mailto:dromitlabs@gmail.com>>:
>> Hi all,
>> I'm trying to run Flink using a local environment, but on an Ignite node to achieve
collocation (as mentioned in my previous message on this list).
>> Have a look at the code in [1]. It's pretty simple, but I'm getting a "cannot load
user class" error as shown in [2].
>> If you check line #29 on the code, I'm able to create an instance of class Test,
and it's the same context from which I'm creating the Flink job. Shouldn't it work provided
I'm using a local environment?
>> It would be really nice to be able to inject a ClassLoader into the chunk of code
that creates the job. Is this currently possible?
>> Any fix or workaround is appreciated!
>> Best,
>> Matt
>> [1] https://gist.github.com/f248187b9638023b95ba8bd9d7f06215 <https://gist.github.com/f248187b9638023b95ba8bd9d7f06215>
>> [2] https://gist.github.com/796ee05425535ece1736df7b1e884cce <https://gist.github.com/796ee05425535ece1736df7b1e884cce>

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