rename to addImmutableStateIfNotExists

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/MonotonicallyIncreasingID.scala

@@ -68,7 +68,7 @@ case class MonotonicallyIncreasingID() extends LeafExpression with Nondeterminis
     val countTerm = ctx.freshName("count")
     val partitionMaskTerm = "partitionMask"
     ctx.addMutableState(ctx.JAVA_LONG, countTerm)
-    ctx.addSingleMutableState(ctx.JAVA_LONG, partitionMaskTerm)
+    ctx.addImmutableStateIfNotExists(ctx.JAVA_LONG, partitionMaskTerm)
     ctx.addPartitionInitializationStatement(s"$countTerm = 0L;")
     ctx.addPartitionInitializationStatement(s"$partitionMaskTerm = ((long) partitionIndex) << 33;")
 

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/SparkPartitionID.scala

@@ -44,7 +44,7 @@ case class SparkPartitionID() extends LeafExpression with Nondeterministic {
 
   override def doGenCode(ctx: CodegenContext, ev: ExprCode): ExprCode = {
     val idTerm = "partitionId"
-    ctx.addSingleMutableState(ctx.JAVA_INT, idTerm)
+    ctx.addImmutableStateIfNotExists(ctx.JAVA_INT, idTerm)
     ctx.addPartitionInitializationStatement(s"$idTerm = partitionIndex;")
     ev.copy(code = s"final ${ctx.javaType(dataType)} ${ev.value} = $idTerm;", isNull = "false")
   }

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/codegen/CodeGenerator.scala

@@ -195,17 +195,20 @@ class CodegenContext {
   }
 
   /**
-   * Add a mutable state as a field to the generated class only if it does not exist yet a field
+   * Add an immutable state as a field to the generated class only if it does not exist yet a field
    * with that name. This helps reducing the number of the generated class' fields, since the same
    * variable can be reused by many functions.
    *
+   * Even though the added variables are not declared as final, they should never be reassigned in
+   * the generated code to prevent errors and unexpected behaviors.
+   *
    * Internally, this method calls `addMutableState`.
    *
    * @param javaType Java type of the field.
    * @param variableName Name of the field.
    * @param initCode The statement(s) to put into the init() method to initialize this field.
    */
-  def addSingleMutableState(
+  def addImmutableStateIfNotExists(
       javaType: String,
       variableName: String,
       initCode: String = ""): Unit = {

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/datetimeExpressions.scala

@@ -444,7 +444,8 @@ case class DayOfWeek(child: Expression) extends UnaryExpression with ImplicitCas
       val cal = classOf[Calendar].getName
       val c = "calDayOfWeek"
       val dtu = DateTimeUtils.getClass.getName.stripSuffix("$")
-      ctx.addSingleMutableState(cal, c, s"""$c = $cal.getInstance($dtu.getTimeZone("UTC"));""")
+      ctx.addImmutableStateIfNotExists(cal, c,
+        s"""$c = $cal.getInstance($dtu.getTimeZone("UTC"));""")
       s"""
         $c.setTimeInMillis($time * 1000L * 3600L * 24L);
         ${ev.value} = $c.get($cal.DAY_OF_WEEK);
@@ -486,7 +487,7 @@ case class WeekOfYear(child: Expression) extends UnaryExpression with ImplicitCa
       val cal = classOf[Calendar].getName
       val c = "calWeekOfYear"
       val dtu = DateTimeUtils.getClass.getName.stripSuffix("$")
-      ctx.addSingleMutableState(cal, c,
+      ctx.addImmutableStateIfNotExists(cal, c,
         s"""
            |$c = $cal.getInstance($dtu.getTimeZone("UTC"));
            |$c.setFirstDayOfWeek($cal.MONDAY);
@@ -1019,7 +1020,8 @@ case class FromUTCTimestamp(left: Expression, right: Expression)
         val tzClass = classOf[TimeZone].getName
         val dtu = DateTimeUtils.getClass.getName.stripSuffix("$")
         ctx.addMutableState(tzClass, tzTerm, s"""$tzTerm = $dtu.getTimeZone("$tz");""")
-        ctx.addSingleMutableState(tzClass, utcTerm, s"""$utcTerm = $dtu.getTimeZone("UTC");""")
+        ctx.addImmutableStateIfNotExists(tzClass, utcTerm,
+          s"""$utcTerm = $dtu.getTimeZone("UTC");""")
         val eval = left.genCode(ctx)
         ev.copy(code = s"""
            |${eval.code}
@@ -1195,7 +1197,8 @@ case class ToUTCTimestamp(left: Expression, right: Expression)
         val tzClass = classOf[TimeZone].getName
         val dtu = DateTimeUtils.getClass.getName.stripSuffix("$")
         ctx.addMutableState(tzClass, tzTerm, s"""$tzTerm = $dtu.getTimeZone("$tz");""")
-        ctx.addSingleMutableState(tzClass, utcTerm, s"""$utcTerm = $dtu.getTimeZone("UTC");""")
+        ctx.addImmutableStateIfNotExists(tzClass, utcTerm,
+          s"""$utcTerm = $dtu.getTimeZone("UTC");""")
         val eval = left.genCode(ctx)
         ev.copy(code = s"""
            |${eval.code}

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/objects/objects.scala

@@ -1169,7 +1169,7 @@ case class EncodeUsingSerializer(child: Expression, kryo: Boolean)
          $serializer = ($serializerInstanceClass) new $serializerClass($env.conf()).newInstance();
        }
      """
-    ctx.addSingleMutableState(serializerInstanceClass, serializer, serializerInit)
+    ctx.addImmutableStateIfNotExists(serializerInstanceClass, serializer, serializerInit)
 
     // Code to serialize.
     val input = child.genCode(ctx)
@@ -1218,7 +1218,7 @@ case class DecodeUsingSerializer[T](child: Expression, tag: ClassTag[T], kryo: B
          $serializer = ($serializerInstanceClass) new $serializerClass($env.conf()).newInstance();
        }
      """
-    ctx.addSingleMutableState(serializerInstanceClass, serializer, serializerInit)
+    ctx.addImmutableStateIfNotExists(serializerInstanceClass, serializer, serializerInit)
 
     // Code to deserialize.
     val input = child.genCode(ctx)

sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/expressions/CodeGenerationSuite.scala

@@ -406,11 +406,11 @@ class CodeGenerationSuite extends SparkFunSuite with ExpressionEvalHelper {
     val ctx = new CodegenContext
     val mutableState1 = "field1"
     val mutableState2 = "field2"
-    ctx.addSingleMutableState("int", mutableState1)
-    ctx.addSingleMutableState("int", mutableState1)
-    ctx.addSingleMutableState("String", mutableState2)
-    ctx.addSingleMutableState("int", mutableState1)
-    ctx.addSingleMutableState("String", mutableState2)
+    ctx.addImmutableStateIfNotExists("int", mutableState1)
+    ctx.addImmutableStateIfNotExists("int", mutableState1)
+    ctx.addImmutableStateIfNotExists("String", mutableState2)
+    ctx.addImmutableStateIfNotExists("int", mutableState1)
+    ctx.addImmutableStateIfNotExists("String", mutableState2)
     assert(ctx.mutableStates.length == 2)
   }
 }