Prevent race condition in TypeHandlerRegistry

Author: Pavel Lyubinskiy

src/main/java/org/apache/ibatis/type/TypeHandlerRegistry.java

@@ -393,9 +393,11 @@ private void register(Type javaType, JdbcType jdbcType, TypeHandler<?> handler)
       Map<JdbcType, TypeHandler<?>> map = typeHandlerMap.get(javaType);
       if (map == null || map == NULL_TYPE_HANDLER_MAP) {
         map = new HashMap<>();
+        map.put(jdbcType, handler);
         typeHandlerMap.put(javaType, map);
+      } else {
+        map.put(jdbcType, handler);
       }
-      map.put(jdbcType, handler);
     }
     allTypeHandlersMap.put(handler.getClass(), handler);
   }

src/test/java/org/apache/ibatis/submitted/typehandlerregistry_race_condition/TestEnum.java

@@ -0,0 +1,6 @@
+package org.apache.ibatis.submitted.typehandlerregistry_race_condition;
+
+enum TestEnum {
+  ONE,
+  TWO
+}

src/test/java/org/apache/ibatis/submitted/typehandlerregistry_race_condition/TypeHandlerRegistryHasHandlerRaceConditionTest.java

@@ -0,0 +1,70 @@
+/**
+ * Copyright 2009-2019 the original author or authors.
+ * <p>
+ * Licensed 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
+ * <p>
+ * http://www.apache.org/licenses/LICENSE-2.0
+ * <p>
+ * 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.ibatis.submitted.typehandlerregistry_race_condition;
+
+import org.apache.ibatis.type.JdbcType;
+import org.apache.ibatis.type.TypeHandlerRegistry;
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.testcontainers.shaded.com.google.common.util.concurrent.Futures;
+
+import java.util.List;
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.Future;
+import java.util.stream.Collectors;
+import java.util.stream.IntStream;
+
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+class TypeHandlerRegistryHasHandlerRaceConditionTest {
+
+  private static final int THREAD_COUNT = 4;
+
+  private ExecutorService executorService;
+
+  @BeforeEach
+  void setUp() {
+    executorService = Executors.newFixedThreadPool(THREAD_COUNT);
+  }
+
+  @AfterEach
+  void setDown() {
+    executorService.shutdownNow();
+  }
+
+  @Test
+  void shouldAutoRegisterEnumTypeInMultiThreadEnvironment() {
+    for (int iteration = 0; iteration < 1000; iteration++) {
+      TypeHandlerRegistry typeHandlerRegistry = new TypeHandlerRegistry();
+      CountDownLatch startLatch = new CountDownLatch(1);
+
+      List<Future<Object>> taskResults = IntStream.range(0, THREAD_COUNT)
+        .mapToObj(taskIndex -> executorService.submit(() -> {
+          startLatch.await();
+          assertTrue(typeHandlerRegistry.hasTypeHandler(TestEnum.class, JdbcType.VARCHAR),
+            "TypeHandler not registered");
+          return null;
+        })).collect(Collectors.toList());
+
+      startLatch.countDown();
+      taskResults.forEach(Futures::getUnchecked);
+    }
+  }
+
+}