name the ForkJoinPool threads

fixes #4329

Author: vladak

opengrok-indexer/src/main/java/org/opengrok/indexer/configuration/OpenGrokThreadFactory.java

@@ -18,7 +18,7 @@
  */
 
 /*
- * Copyright (c) 2022, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2022, 2023, Oracle and/or its affiliates. All rights reserved.
  */
 package org.opengrok.indexer.configuration;
 
@@ -33,6 +33,8 @@
 public class OpenGrokThreadFactory implements ThreadFactory {
     private final String threadPrefix;
 
+    public static final String PREFIX = "OpenGrok-";
+
     public OpenGrokThreadFactory(String name) {
         if (!name.endsWith("-")) {
             threadPrefix = name + "-";
@@ -44,7 +46,7 @@ public OpenGrokThreadFactory(String name) {
     @Override
     public Thread newThread(@NotNull Runnable runnable) {
         Thread thread = Executors.defaultThreadFactory().newThread(runnable);
-        thread.setName("OpenGrok-" + threadPrefix + thread.getId());
+        thread.setName(PREFIX + threadPrefix + thread.getId());
         return thread;
     }
 }

opengrok-indexer/src/main/java/org/opengrok/indexer/index/IndexerParallelizer.java

@@ -26,6 +26,7 @@
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Executors;
 import java.util.concurrent.ForkJoinPool;
+import java.util.concurrent.ForkJoinWorkerThread;
 import java.util.concurrent.ScheduledThreadPoolExecutor;
 
 import org.opengrok.indexer.analysis.Ctags;
@@ -37,6 +38,8 @@
 import org.opengrok.indexer.util.ObjectFactory;
 import org.opengrok.indexer.util.ObjectPool;
 
+import static java.util.concurrent.ForkJoinPool.defaultForkJoinWorkerThreadFactory;
+
 /**
  * Represents a container for executors that enable parallelism for indexing
  * across projects and repositories and also within any {@link IndexDatabase}
@@ -230,7 +233,11 @@ private void bounceXrefWatcherExecutor() {
 
     private void createLazyForkJoinPool() {
         lzForkJoinPool = LazilyInstantiate.using(() ->
-                new ForkJoinPool(indexingParallelism));
+                new ForkJoinPool(indexingParallelism, forkJoinPool -> {
+                    ForkJoinWorkerThread thread = defaultForkJoinWorkerThreadFactory.newThread(forkJoinPool);
+                    thread.setName(OpenGrokThreadFactory.PREFIX + "ForkJoinPool-" + thread.getId());
+                    return thread;
+                }, null, false));
     }
 
     private void createLazyCtagsPool() {