[SPARK-8306] [SQL] AddJar command needs to set the new class loader to the HiveConf inside executionHive.state.

sql/hive/src/main/scala/org/apache/spark/sql/hive/client/ClientWrapper.scala

@@ -95,6 +95,7 @@ private[hive] class ClientWrapper(
     case hive.v14 => new Shim_v0_14()
   }
 
+  // Create an internal session state for this ClientWrapper.
   val state = {
     val original = Thread.currentThread().getContextClassLoader
     Thread.currentThread().setContextClassLoader(getClass.getClassLoader)
@@ -131,8 +132,15 @@ private[hive] class ClientWrapper(
    */
   private def withHiveState[A](f: => A): A = synchronized {
     val original = Thread.currentThread().getContextClassLoader
+    // This setContextClassLoader is used for Hive 0.12's metastore since Hive 0.12 will not
+    // internally override the context class loader of the current thread with the class loader
+    // associated with the HiveConf in `state`.
     Thread.currentThread().setContextClassLoader(getClass.getClassLoader)
+    // Set the thread local metastore client to the client associated with this ClientWrapper.
     Hive.set(client)
+    // Starting from Hive 0.13.0, setCurrentSessionState will use the classLoader associated
+    // with the HiveConf in `state` to override the context class loader of the current
+    // thread.
     shim.setCurrentSessionState(state)
     val ret = try f finally {
       Thread.currentThread().setContextClassLoader(original)

sql/hive/src/main/scala/org/apache/spark/sql/hive/execution/commands.scala

@@ -91,9 +91,15 @@ case class AddJar(path: String) extends RunnableCommand {
     val jarURL = new java.io.File(path).toURL
     val newClassLoader = new java.net.URLClassLoader(Array(jarURL), currentClassLoader)
     Thread.currentThread.setContextClassLoader(newClassLoader)
-    org.apache.hadoop.hive.ql.metadata.Hive.get().getConf().setClassLoader(newClassLoader)
-
-    // Add jar to isolated hive classloader
+    // We need to explicitly set the class loader associated with the conf in executionHive's
+    // state because this class loader will be used as the context class loader of the current
+    // thread to execute any Hive command.
+    // We cannot use `org.apache.hadoop.hive.ql.metadata.Hive.get().getConf()` because Hive.get()
+    // returns the value of a thread local variable and its HiveConf may not be the HiveConf
+    // associated with `executionHive.state` (for example, HiveContext is created in one thread
+    // and then add jar is called from another thread).
+    hiveContext.executionHive.state.getConf.setClassLoader(newClassLoader)
+    // Add jar to isolated hive (metadataHive) class loader.
     hiveContext.runSqlHive(s"ADD JAR $path")
 
     // Add jar to executors

sql/hive/src/test/scala/org/apache/spark/sql/hive/execution/SQLQuerySuite.scala

@@ -934,4 +934,32 @@ class SQLQuerySuite extends QueryTest {
       sql("set hive.exec.dynamic.partition.mode=strict")
     }
   }
+
+  test("Call add jar in a different thread (SPARK-8306)") {
+    @volatile var error: Option[Throwable] = None
+    val thread = new Thread {
+      override def run() {
+        // To make sure this test works, this jar should not be loaded in another place.
+        TestHive.sql(
+          s"ADD JAR ${TestHive.getHiveFile("hive-contrib-0.13.1.jar").getCanonicalPath()}")
+        try {
+          TestHive.sql(
+            """
+              |CREATE TEMPORARY FUNCTION example_max
+              |AS 'org.apache.hadoop.hive.contrib.udaf.example.UDAFExampleMax'
+            """.stripMargin)
+        } catch {
+          case throwable: Throwable =>
+            error = Some(throwable)
+        }
+      }
+    }
+    thread.start()
+    thread.join()
+    error match {
+      case Some(throwable) =>
+        fail("CREATE TEMPORARY FUNCTION should not fail.", throwable)
+      case None => // OK
+    }
+  }
 }