[SPARK-5952][SQL] Lock when using hive metastore client

Author: Michael Armbrust <michael@databricks.com>

Closes #4746 from marmbrus/hiveLock and squashes the following commits:

8b871cf [Michael Armbrust] [SPARK-5952][SQL] Lock when using hive metastore client

sql/hive/src/main/scala/org/apache/spark/sql/hive/HiveMetastoreCatalog.scala

@@ -52,6 +52,7 @@ private[hive] class HiveMetastoreCatalog(hive: HiveContext) extends Catalog with
   /** Connection to hive metastore.  Usages should lock on `this`. */
   protected[hive] val client = Hive.get(hive.hiveconf)
 
+  /** Usages should lock on `this`. */
   protected[hive] lazy val hiveWarehouse = new Warehouse(hive.hiveconf)
 
   // TODO: Use this everywhere instead of tuples or databaseName, tableName,.
@@ -65,7 +66,9 @@ private[hive] class HiveMetastoreCatalog(hive: HiveContext) extends Catalog with
     val cacheLoader = new CacheLoader[QualifiedTableName, LogicalPlan]() {
       override def load(in: QualifiedTableName): LogicalPlan = {
         logDebug(s"Creating new cached data source for $in")
-        val table = client.getTable(in.database, in.name)
+        val table = synchronized {
+          client.getTable(in.database, in.name)
+        }
         val schemaString = table.getProperty("spark.sql.sources.schema")
         val userSpecifiedSchema =
           if (schemaString == null) {
@@ -134,15 +137,18 @@ private[hive] class HiveMetastoreCatalog(hive: HiveContext) extends Catalog with
     }
   }
 
-  def hiveDefaultTableFilePath(tableName: String): String = {
+  def hiveDefaultTableFilePath(tableName: String): String = synchronized {
     val currentDatabase = client.getDatabase(hive.sessionState.getCurrentDatabase)
+
     hiveWarehouse.getTablePath(currentDatabase, tableName).toString
   }
 
-  def tableExists(tableIdentifier: Seq[String]): Boolean = {
+  def tableExists(tableIdentifier: Seq[String]): Boolean = synchronized {
     val tableIdent = processTableIdentifier(tableIdentifier)
-    val databaseName = tableIdent.lift(tableIdent.size - 2).getOrElse(
-      hive.sessionState.getCurrentDatabase)
+    val databaseName =
+      tableIdent
+        .lift(tableIdent.size - 2)
+        .getOrElse(hive.sessionState.getCurrentDatabase)
     val tblName = tableIdent.last
     client.getTable(databaseName, tblName, false) != null
   }
@@ -219,7 +225,7 @@ private[hive] class HiveMetastoreCatalog(hive: HiveContext) extends Catalog with
     }
   }
 
-  override def getTables(databaseName: Option[String]): Seq[(String, Boolean)] = {
+  override def getTables(databaseName: Option[String]): Seq[(String, Boolean)] = synchronized {
     val dbName = if (!caseSensitive) {
       if (databaseName.isDefined) Some(databaseName.get.toLowerCase) else None
     } else {