[jira] [Created] (SPARK-9339) Use of Class.forName(String) should be replaced with version taking classloader

["Mridul Muralidharan (JIRA)" <ji...@apache.org>]

Mridul Muralidharan created SPARK-9339:
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             Summary: Use of Class.forName(String) should be replaced with version taking classloader
                 Key: SPARK-9339
                 URL: https://issues.apache.org/jira/browse/SPARK-9339
             Project: Spark
          Issue Type: Bug
            Reporter: Mridul Muralidharan



In spark, multiple places have ability to take external class as input - example: listener.
Other than in specific cases (like SparkEnv), the code typically calls Class.forName(clazzName)

This works when the class is from within spark - but when the referenced class is from external jar (user provided), it tends to fail.

For example, in 1.3 we get this when using custom listener:

ERROR ApplicationMaster: User class threw exception: Exception when registering SparkListener
org.apache.spark.SparkException: Exception when registering SparkListener
	at org.apache.spark.SparkContext.setupAndStartListenerBus(SparkContext.scala:1726)
	at org.apache.spark.SparkContext.<init>(SparkContext.scala:429)
	at org.apache.spark.SparkContext.<init>(SparkContext.scala:134)
	at com.yahoo.corp.yst.webmap.spark.PageRankDataGenerator$.main(PageRankDataGenerator.scala:170)
	at com.yahoo.corp.yst.webmap.spark.PageRankDataGenerator.main(PageRankDataGenerator.scala)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:606)
	at org.apache.spark.deploy.yarn.ApplicationMaster$$anon$2.run(ApplicationMaster.scala:480)
Caused by: java.lang.ClassNotFoundException: <MySparkListener>
	at java.net.URLClassLoader$1.run(URLClassLoader.java:366)
	at java.net.URLClassLoader$1.run(URLClassLoader.java:355)
	at java.security.AccessController.doPrivileged(Native Method)
	at java.net.URLClassLoader.findClass(URLClassLoader.java:354)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:425)
	at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:308)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:358)
	at java.lang.Class.forName0(Native Method)
	at java.lang.Class.forName(Class.java:190)
	at org.apache.spark.SparkContext$$anonfun$setupAndStartListenerBus$1.apply(SparkContext.scala:1694)
	at org.apache.spark.SparkContext$$anonfun$setupAndStartListenerBus$1.apply(SparkContext.scala:1691)
	at scala.collection.IndexedSeqOptimized$class.foreach(IndexedSeqOptimized.scala:33)
	at scala.collection.mutable.WrappedArray.foreach(WrappedArray.scala:34)
	at org.apache.spark.SparkContext.setupAndStartListenerBus(SparkContext.scala:1691)
	... 9 more



Instead of
"val listenerClass = Class.forName(className)" in SparkContext.setupAndStartListenerBus, we should use 
"val listenerClass = Class.forName(className, true, Thread.currentThread().getContextClassLoader)"

Note - this is a common pattern in spark, and might be relevant elsewhere too.



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