[Spark] Handle concurrent CREATE TABLE IF NOT EXISTS ... LIKE ... table commands (#3306)

#### Which Delta project/connector is this regarding?
- [x] Spark
- [ ] Standalone
- [ ] Flink
- [ ] Kernel
- [ ] Other (fill in here)

## Description

When 2 or more CREATE TABLE IF NOT EXISTS table commands are run
concurrently, they both think the table doesn't exist yet and the second
command fails with TABLE_ALREADY_EXISTS error.

With this PR, we aim to make sure the second command end up in a no-op
instead of a failure.

## How was this patch tested?

UTs

## Does this PR introduce _any_ user-facing changes?

No

Author: sumeet-db

spark/src/main/scala/org/apache/spark/sql/delta/commands/CreateDeltaTableCommand.scala

@@ -603,7 +603,7 @@ case class CreateDeltaTableCommand(
       case TableCreationModes.Create =>
         spark.sessionState.catalog.createTable(
           cleaned,
-          ignoreIfExists = existingTableOpt.isDefined,
+          ignoreIfExists = existingTableOpt.isDefined || mode == SaveMode.Ignore,
           validateLocation = false)
       case TableCreationModes.Replace | TableCreationModes.CreateOrReplace
           if existingTableOpt.isDefined =>

spark/src/test/scala/org/apache/spark/sql/delta/DeltaCreateTableLikeSuite.scala

@@ -17,14 +17,21 @@
 package org.apache.spark.sql.delta
 
 import java.io.File
+import java.net.URI
+import java.util.UUID
 
+import org.apache.spark.sql.delta.catalog.DeltaCatalog
+import org.apache.spark.sql.delta.commands.{CreateDeltaTableCommand, TableCreationModes}
 import org.apache.spark.sql.delta.test.DeltaSQLCommandTest
 import org.scalatest.exceptions.TestFailedException
 
 import org.apache.spark.sql.QueryTest
+import org.apache.spark.sql.SaveMode
 import org.apache.spark.sql.catalyst.TableIdentifier
+import org.apache.spark.sql.catalyst.catalog.{CatalogStorageFormat, CatalogTable, CatalogTableType}
 import org.apache.spark.sql.functions.lit
 import org.apache.spark.sql.test.SharedSparkSession
+import org.apache.spark.sql.types.StructType
 
 class DeltaCreateTableLikeSuite extends QueryTest
   with SharedSparkSession
@@ -277,6 +284,42 @@ class DeltaCreateTableLikeSuite extends QueryTest
     }
   }
 
+  test("concurrent create Managed Catalog table commands should not fail") {
+    withTempDir { dir =>
+      withTable("t") {
+        def getCatalogTable: CatalogTable = {
+          val storage = CatalogStorageFormat.empty.copy(
+            locationUri = Some(new URI(s"$dir/${UUID.randomUUID().toString}")))
+          val catalogTableTarget = CatalogTable(
+            identifier = TableIdentifier("t"),
+            tableType = CatalogTableType.MANAGED,
+            storage = storage,
+            provider = Some("delta"),
+            schema = new StructType().add("id", "long"))
+          new DeltaCatalog()
+            .verifyTableAndSolidify(
+              tableDesc = catalogTableTarget,
+              query = None,
+              maybeClusterBySpec = None)
+        }
+        CreateDeltaTableCommand(
+          getCatalogTable,
+          existingTableOpt = None,
+          mode = SaveMode.Ignore,
+          query = None,
+          operation = TableCreationModes.Create).run(spark)
+        assert(spark.sessionState.catalog.tableExists(TableIdentifier("t")))
+        CreateDeltaTableCommand(
+          getCatalogTable,
+          existingTableOpt = None, // Set to None to simulate concurrent table creation commands.
+          mode = SaveMode.Ignore,
+          query = None,
+          operation = TableCreationModes.Create).run(spark)
+        assert(spark.sessionState.catalog.tableExists(TableIdentifier("t")))
+      }
+    }
+  }
+
   test("CREATE TABLE LIKE where sourceTable is a json table") {
     val srcTbl = "srcTbl"
     val targetTbl = "targetTbl"