I agree, this would be nice to support in Flink.
The important parts are on the client side (which may be embedded). The
classloaders are used there as part of the de-serialization of messages
that contain user-defined types (such as in collect() or in accumulators
and in exception reporting).
How are you starting the program in your web-app, by the way?
If you would be up for contributing this fix, that would be great! One
could approach this in two ways:
- Simple, but not sure if completely future proof: we take always the
context classloader as the parent, and if that is null, the system class
loader
- More elaborate: We allow to set a root classloader on the
ExecutionEnvironment. That one should be passed as parent class loader to
the Remote Executor and the Client.
Greetings,
Stephan
On Mon, Dec 21, 2015 at 4:41 PM, peterpanne <e...@peukert.org> wrote:
> I identified the root-cause of the problem:
>
> When the FlinkUserCodeClassLoader ist created it simply instantiates the
> URLClassLoader which takes the System-Classloader as parent. However in the
> web-application-setting the current thread-webapp-classloader should be
> taken. I tried to change the class slightly to take the "right" threads
> class loader as parent.
> private static class FlinkUserCodeClassLoader extends URLClassLoader {
> public FlinkUserCodeClassLoader(URL[] urls) {
> super(urls,
> Thread.currentThread().getContextClassLoader());}}
>
> Unfortunately there are multiple places where the system-classloader ist
> taken instead of the thread class loader:
>
> flink-runtime/src/main/java/org/apache/flink/runtime/accumulators/AccumulatorSnapshot.java
> That solved my problem for the moment.
> However, I am not sure if that introduces problems somewhere else. In
> theory
> it should not be critical since the web-appclassloader simply introduces an
> additional level of classes to look for.
>
> It would cool if that problem could be resolved in flink ;-)
>
>
>
>
>
> --
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