[SPARK-9448][SQL] GenerateUnsafeProjection should not share expressions across instances.

We accidentally moved the list of expressions from the generated code instance to the class wrapper, and as a result, different threads are sharing the same set of expressions, which cause problems for expressions with mutable state.

This pull request fixed that problem, and also added unit tests for all codegen classes, except GeneratedOrdering (which will never need any expressions since sort now only accepts bound references.

Author: Reynold Xin <rxin@databricks.com>

Closes #7759 from rxin/SPARK-9448 and squashes the following commits:

c09b50f [Reynold Xin] [SPARK-9448][SQL] GenerateUnsafeProjection should not share expressions across instances.

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

@@ -256,18 +256,18 @@ object GenerateUnsafeProjection extends CodeGenerator[Seq[Expression], UnsafePro
     eval.code = createCode(ctx, eval, expressions)
 
     val code = s"""
-      private $exprType[] expressions;
+      public Object generate($exprType[] exprs) {
-
+        return new SpecificProjection(exprs);
-      public Object generate($exprType[] expr) {
-        this.expressions = expr;
-        return new SpecificProjection();
       }
 
       class SpecificProjection extends ${classOf[UnsafeProjection].getName} {
 
+        private $exprType[] expressions;
+
         ${declareMutableStates(ctx)}
 
-        public SpecificProjection() {
+        public SpecificProjection($exprType[] expressions) {
+          this.expressions = expressions;
           ${initMutableStates(ctx)}
         }
 

sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/expressions/codegen/CodegenExpressionCachingSuite.scala

@@ -0,0 +1,90 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.spark.sql.catalyst.expressions.codegen
+
+import org.apache.spark.SparkFunSuite
+import org.apache.spark.sql.catalyst.InternalRow
+import org.apache.spark.sql.catalyst.expressions.{UnsafeProjection, LeafExpression}
+import org.apache.spark.sql.types.{BooleanType, DataType}
+
+/**
+ * A test suite that makes sure code generation handles expression internally states correctly.
+ */
+class CodegenExpressionCachingSuite extends SparkFunSuite {
+
+  test("GenerateUnsafeProjection") {
+    val expr1 = MutableExpression()
+    val instance1 = UnsafeProjection.create(Seq(expr1))
+    assert(instance1.apply(null).getBoolean(0) === false)
+
+    val expr2 = MutableExpression()
+    expr2.mutableState = true
+    val instance2 = UnsafeProjection.create(Seq(expr2))
+    assert(instance1.apply(null).getBoolean(0) === false)
+    assert(instance2.apply(null).getBoolean(0) === true)
+  }
+
+  test("GenerateProjection") {
+    val expr1 = MutableExpression()
+    val instance1 = GenerateProjection.generate(Seq(expr1))
+    assert(instance1.apply(null).getBoolean(0) === false)
+
+    val expr2 = MutableExpression()
+    expr2.mutableState = true
+    val instance2 = GenerateProjection.generate(Seq(expr2))
+    assert(instance1.apply(null).getBoolean(0) === false)
+    assert(instance2.apply(null).getBoolean(0) === true)
+  }
+
+  test("GenerateMutableProjection") {
+    val expr1 = MutableExpression()
+    val instance1 = GenerateMutableProjection.generate(Seq(expr1))()
+    assert(instance1.apply(null).getBoolean(0) === false)
+
+    val expr2 = MutableExpression()
+    expr2.mutableState = true
+    val instance2 = GenerateMutableProjection.generate(Seq(expr2))()
+    assert(instance1.apply(null).getBoolean(0) === false)
+    assert(instance2.apply(null).getBoolean(0) === true)
+  }
+
+  test("GeneratePredicate") {
+    val expr1 = MutableExpression()
+    val instance1 = GeneratePredicate.generate(expr1)
+    assert(instance1.apply(null) === false)
+
+    val expr2 = MutableExpression()
+    expr2.mutableState = true
+    val instance2 = GeneratePredicate.generate(expr2)
+    assert(instance1.apply(null) === false)
+    assert(instance2.apply(null) === true)
+  }
+
+}
+
+
+/**
+ * An expression with mutable state so we can change it freely in our test suite.
+ */
+case class MutableExpression() extends LeafExpression with CodegenFallback {
+  var mutableState: Boolean = false
+  override def eval(input: InternalRow): Any = mutableState
+
+  override def nullable: Boolean = false
+  override def dataType: DataType = BooleanType
+}