[jira] [Created] (SPARK-23598) WholeStageCodegen can lead to IllegalAccessError calling append for HashAggregateExec

["David Vogelbacher (JIRA)" <ji...@apache.org>]

David Vogelbacher created SPARK-23598:
-----------------------------------------

             Summary: WholeStageCodegen can lead to IllegalAccessError  calling append for HashAggregateExec
                 Key: SPARK-23598
                 URL: https://issues.apache.org/jira/browse/SPARK-23598
             Project: Spark
          Issue Type: Bug
          Components: Spark Core
    Affects Versions: 2.4.0
            Reporter: David Vogelbacher


Got the following stacktrace for a large QueryPlan using WholeStageCodeGen:
{code:java}
java.lang.IllegalAccessError: tried to access method org.apache.spark.sql.execution.BufferedRowIterator.append(Lorg/apache/spark/sql/catalyst/InternalRow;)V from class org.apache.spark.sql.catalyst.expressions.GeneratedClass$GeneratedIteratorForCodegenStage7$agg_NestedClass
at org.apache.spark.sql.catalyst.expressions.GeneratedClass$GeneratedIteratorForCodegenStage7$agg_NestedClass.agg_doAggregateWithKeysOutput$(Unknown Source)
at org.apache.spark.sql.catalyst.expressions.GeneratedClass$GeneratedIteratorForCodegenStage7.processNext(Unknown Source)
at org.apache.spark.sql.execution.BufferedRowIterator.hasNext(BufferedRowIterator.java:43)
at org.apache.spark.sql.execution.WholeStageCodegenExec$$anonfun$10$$anon$1.hasNext(WholeStageCodegenExec.scala:614)
at scala.collection.Iterator$$anon$11.hasNext(Iterator.scala:408)
at org.apache.spark.shuffle.sort.BypassMergeSortShuffleWriter.write(BypassMergeSortShuffleWriter.java:125)
at org.apache.spark.scheduler.ShuffleMapTask.runTask(ShuffleMapTask.scala:96)
at org.apache.spark.scheduler.ShuffleMapTask.runTask(ShuffleMapTask.scala:53)
at org.apache.spark.scheduler.Task.run(Task.scala:109)
at org.apache.spark.executor.Executor$TaskRunner.run(Executor.scala:345)
{code}

After disabling codegen, everything works.

The root cause seems to be that we are trying to call the protected _append_ method of [BufferedRowIterator|https://github.com/apache/spark/blob/master/sql/core/src/main/java/org/apache/spark/sql/execution/BufferedRowIterator.java#L68] __ from an inner-class of a sub-class that is loaded by a different class-loader (after codegen compilation).

[https://docs.oracle.com/javase/specs/jvms/se7/html/jvms-5.html#jvms-5.4.4] states that a protected method _R_ can be accessed only if one of the following two conditions is fulfilled:
 # R is protected and is declared in a class C, and D is either a subclass of C or C itself. Furthermore, if R is not static, then the symbolic reference to R must contain a symbolic reference to a class T, such that T is either a subclass of D, a superclass of D, or D itself.
 # R is either protected or has default access (that is, neither public nor protected nor private), and is declared by a class in the same run-time package as D.

2.) doesn't apply as we have loaded the class with a different class loader (and are in a different package) and 1.) doesn't apply because we are apparently trying to call the method from an inner class of a subclass of _BufferedRowIterator_.



Looking at the Code path of _WholeStageCodeGen_, the following happens:
 # In [WholeStageCodeGen|https://github.com/apache/spark/blob/master/sql/core/src/main/scala/org/apache/spark/sql/execution/WholeStageCodegenExec.scala#L527], we create the subclass of _BufferedRowIterator_, along with a _processNext_ method for processing the output of the child plan.
 # In the child, which is a [HashAggregateExec|https://github.com/apache/spark/blob/master/sql/core/src/main/scala/org/apache/spark/sql/execution/aggregate/HashAggregateExec.scala#L517], we create the method which shows up at the top of the stack trace (called _doAggregateWithKeysOutput_ )
 # We add this method to the compiled code invoking _addNewFunction_ of [CodeGenerator|https://github.com/apache/spark/blob/master/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/codegen/CodeGenerator.scala#L460]

Now, this method states that:
{noformat}
If the code for the `OuterClass` grows too large, the function will be inlined into a new private, inner class
{noformat}
This indeed seems to happen: the _doAggregateWithKeysOutput_ method is put into a new private inner class. Thus, it doesn't have access to the protected _append_ method anymore but still tries to call it, which results in the ___IllegalAccessError._ 

Possible fixes:
 * Pass in the _inlineToOuterClass_ flag when invoking __ _addNewFunction_
 * Make the _append_ method public
 * Re-declare the _append_ method in the generated subclass (just invoking _super_). This way, inner classes should have access to it.

 



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