serkan-ozal's final submission:

- start worker thread in advance
- increase region count

src/main/java/dev/morling/onebrc/CalculateAverage_serkan_ozal.java

@@ -37,6 +37,7 @@
 import java.util.TreeMap;
 import java.util.concurrent.Callable;
 import java.util.concurrent.ConcurrentLinkedQueue;
+import java.util.concurrent.CountDownLatch;
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Executors;
 import java.util.concurrent.Future;
@@ -72,7 +73,7 @@ public class CalculateAverage_serkan_ozal {
     private static final int THREAD_COUNT = Runtime.getRuntime().availableProcessors(); // getIntegerConfig("THREAD_COUNT", Runtime.getRuntime().availableProcessors());
     private static final boolean USE_VTHREADS = false; // getBooleanConfig("USE_VTHREADS", false);
     private static final int VTHREAD_COUNT = 1024; // getIntegerConfig("VTHREAD_COUNT", 1024);
-    private static final int REGION_COUNT = 256; // getIntegerConfig("REGION_COUNT", -1);
+    private static final int REGION_COUNT = 512; // getIntegerConfig("REGION_COUNT", -1);
     private static final boolean USE_SHARED_ARENA = true; // getBooleanConfig("USE_SHARED_ARENA", true);
     private static final boolean USE_SHARED_REGION = true; // getBooleanConfig("USE_SHARED_REGION", true);
     private static final int MAP_CAPACITY = 1 << 17; // getIntegerConfig("MAP_CAPACITY", 1 << 17);
@@ -130,8 +131,18 @@ public static void main(String[] args) throws Exception {
             }
 
             List<Task> tasks = new ArrayList<>(regionCount);
-            // Split whole file into regions and create tasks for each region
+            Queue<Task> sharedTasks = new ConcurrentLinkedQueue<>();
+            Request request = new Request(arena, sharedTasks, result);
             List<Future<Response>> futures = new ArrayList<>(regionCount);
+
+            // Start region processors earlier to process tasks for each region
+            for (int i = 0; i < concurrency; i++) {
+                RegionProcessor regionProcessor = createRegionProcessor(request);
+                Future<Response> future = executor.submit(regionProcessor);
+                futures.add(future);
+            }
+
+            // Split whole file into regions and create tasks for each region
             for (int i = 0; i < regionCount; i++) {
                 long endPos = Math.min(fileSize, startPos + regionSize);
                 // Lines might split into different regions.
@@ -144,15 +155,9 @@ public static void main(String[] args) throws Exception {
                 startPos = closestLineEndPos;
             }
 
-            Queue<Task> sharedTasks = new ConcurrentLinkedQueue<>(tasks);
-
-            // Start region processors to process tasks for each region
-            for (int i = 0; i < concurrency; i++) {
-                Request request = new Request(arena, sharedTasks, result);
-                RegionProcessor regionProcessor = createRegionProcessor(request);
-                Future<Response> future = executor.submit(regionProcessor);
-                futures.add(future);
-            }
+            // Submit all tasks
+            sharedTasks.addAll(tasks);
+            request.start();
 
             // Wait processors to complete
             for (Future<Response> future : futures) {
@@ -247,12 +252,14 @@ public Thread newThread(Runnable r) {
      */
     private static class RegionProcessor implements Callable<Response> {
 
+        private final Request request;
         private final Arena arena;
         private final Queue<Task> sharedTasks;
         private final Result result;
         private OpenMap map;
 
         private RegionProcessor(Request request) {
+            this.request = request;
             this.arena = request.arena;
             this.sharedTasks = request.sharedTasks;
             this.result = request.result;
@@ -282,6 +289,8 @@ private void processRegion() throws Exception {
             // If no shared global memory arena is used, create and use its own local memory arena
             Arena a = arenaGiven ? arena : Arena.ofConfined();
             try {
+                request.waitForStart();
+
                 for (Task task = sharedTasks.poll(); task != null; task = sharedTasks.poll()) {
                     boolean regionGiven = task.region != null;
                     MemorySegment r = regionGiven
@@ -562,13 +571,22 @@ private static final class Request {
         private final Arena arena;
         private final Queue<Task> sharedTasks;
         private final Result result;
+        private final CountDownLatch started = new CountDownLatch(1);
 
         private Request(Arena arena, Queue<Task> sharedTasks, Result result) {
             this.arena = arena;
             this.sharedTasks = sharedTasks;
             this.result = result;
         }
 
+        private void waitForStart() throws InterruptedException {
+            started.await();
+        }
+
+        private void start() {
+            started.countDown();
+        }
+
     }
 
     /**