Andrew Kerr updated TOREE-349:
    Attachment: avro-csv-addDeps.scala.ipynb

> ClassCastException when reading Avro from another thread (Toree master / 
> Spark 2.0.0)
> -------------------------------------------------------------------------------------
>                 Key: TOREE-349
>                 URL: https://issues.apache.org/jira/browse/TOREE-349
>             Project: TOREE
>          Issue Type: Bug
>            Reporter: Andrew Kerr
>         Attachments: avro-csv-addDeps.scala.ipynb, 
> avro-csv-threading.scala.ipynb, avro-csv-threading.scala.ipynb, run.sh
> When using Toree (master branch commit 
> e8ecd0623c65ad104045b1797fb27f69b8dfc23f)
> with `--packages=com.databricks:spark-avro_2.11:3.0.1` in `SPARK_OPTS`
> and attempting to load an avro file into a dataframe *in a separate thread*
> then an exception is thrown
> `java.lang.ClassCastException: 
> com.databricks.spark.avro.DefaultSource$SerializableConfiguration cannot be 
> cast to com.databricks.spark.avro.DefaultSource$SerializableConfiguration`
> here
> https://github.com/databricks/spark-avro/blob/v3.0.1/src/main/scala/com/databricks/spark/avro/DefaultSource.scala#L156
> Will attach a Jupyter notebook that illustrates the problem and includes full
> stack trace, with a script showing environment.
> The class that throws the exception `DefaultSource` broadcasts Hadoop config
> and returns an anonymous function that accesses that config. The exception
> occurs when that function is executed and it attempts to access the config.
> This looks like a class loader mismatch problem to me ("Class Identity 
> Crisis").
> With a bit of hacking of `spark-avro` I've seen the class loader for 
> `DefaultSource` when the config is broadcast to be 
> `scala.reflect.internal.util.ScalaClassLoader$URLClassLoader@31ac5411`
> and when the config is read to be
> `org.apache.spark.util.MutableURLClassLoader@3d3fcdb0`
> If a fat jar including `spark-avro` is built and included with `--jars=...`
> then the same problem occurs.
> Interestingly the Spark's included support for CSV uses the same pattern as
> Avro, broadcasting a config, but works as expected as shown in the notebook.
> https://github.com/apache/spark/blob/v2.0.0/sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/csv/CSVFileFormat.scala#L108
> Avro also works as expected when an application fat jar is built and passed 
> to 
> `spark-submit` without involving Toree.

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