[GitHub] [incubator-druid] clintropolis commented on a change in pull request #8578: parallel broker merges on fork join pool

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clintropolis commented on a change in pull request #8578: parallel broker merges on fork join pool
URL: https://github.com/apache/incubator-druid/pull/8578#discussion_r327529254
 
 

 ##########
 File path: processing/src/main/java/org/apache/druid/guice/LifecycleForkJoinPool.java
 ##########
 @@ -0,0 +1,61 @@
+/*
+ * 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.druid.guice;
+
+
+import org.apache.druid.java.util.common.lifecycle.LifecycleStop;
+import org.apache.druid.java.util.common.logger.Logger;
+
+import java.util.concurrent.ForkJoinPool;
+import java.util.concurrent.TimeUnit;
+
+public class LifecycleForkJoinPool extends ForkJoinPool
 
 Review comment:
   This seems to be the cause of mysterious java 9+ compilation issues causing CI failures (my favorite part is how the compiler error doesn't at all specify what is causing the error). `ForkJoinPool` has the `@Contended` annotation, which from javadocs looks like it leaks to subclasses I guess?
   ```
    * <p>The class level {@code @Contended} annotation is not inherited and has
    * no effect on the fields declared in any sub-classes. The effects of all
    * {@code @Contended} annotations, however, remain in force for all
    * subclass instances, providing isolation of all the defined contention
    * groups. Contention group tags are not inherited, and the same tag used
    * in a superclass and subclass, represent distinct contention groups.
   ```
   
   This might be fixed by something like:
   
   ```
   <compilerArgs>
     <arg>--add-exports</arg>
     <arg>java.base/jdk.internal.misc=ALL-UNNAMED</arg>
   </compilerArgs>
   ```
   
   added to jdk9+ profile, but would also require removing all source/target directives into a jdk8 profile I think, since:
   
   ```
    error: option --add-exports not allowed with target 8
   ```
   happens otherwise.
   
   Not sure what is the best thing to do here. it could probably be worked around by I guess having a lifecycle'd module that wraps a `ForkJoinPool` for the provider instead of extending `ForkJoinPool`, since just using `ForkJoinPool` doesn't seem to cause this error in jdk9+, but I'm not sure if that is the better solution, or if we should try to add the compiler args.

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