From 9abc5d265baa1bc5af4e14c9c982d6b4ab4de53f Mon Sep 17 00:00:00 2001
From: Axel Uhl <axel.uhl@sap.com>
Date: Fri, 12 Aug 2016 13:19:00 +0200
Subject: [PATCH] introduced follow-up tasks; wait until executor has finished
 executing all tasks

Change-Id: Ibb1ab9eb8e5dcf1b9cd4acc60bff520931f58c6a
---
 .../OutperformingTheGarbageCollectorTest.java | 37 +++++++++++++------
 1 file changed, 25 insertions(+), 12 deletions(-)

diff --git a/java/com.sap.sailing.domain.test/src/com/sap/sailing/domain/common/test/OutperformingTheGarbageCollectorTest.java b/java/com.sap.sailing.domain.test/src/com/sap/sailing/domain/common/test/OutperformingTheGarbageCollectorTest.java
index efee387f13e..61c8ad3d88d 100644
--- a/java/com.sap.sailing.domain.test/src/com/sap/sailing/domain/common/test/OutperformingTheGarbageCollectorTest.java
+++ b/java/com.sap.sailing.domain.test/src/com/sap/sailing/domain/common/test/OutperformingTheGarbageCollectorTest.java
@@ -1,46 +1,59 @@
 package com.sap.sailing.domain.common.test;
 
+import java.util.HashMap;
 import java.util.Iterator;
 import java.util.Map.Entry;
 import java.util.NoSuchElementException;
 import java.util.Random;
-import java.util.concurrent.ConcurrentHashMap;
-import java.util.concurrent.Executor;
 import java.util.concurrent.LinkedBlockingQueue;
 import java.util.concurrent.ThreadPoolExecutor;
 import java.util.concurrent.TimeUnit;
+import java.util.logging.Level;
 import java.util.logging.Logger;
 
 import org.junit.Test;
 
 public class OutperformingTheGarbageCollectorTest {
     private static final Logger logger = Logger.getLogger(OutperformingTheGarbageCollectorTest.class.getName());
-    private static final int MAX_THREADPOOL_SIZE = 300;
-    private static final int NUMBER_OF_OBJECTS_TO_CREATE = 50000000;
+    private static final int MAX_THREADPOOL_SIZE = 50;
+    private static final int NUMBER_OF_OBJECTS_TO_CREATE_INITIALLY = 50000000;
+    private static final int NUMBER_OF_FOLLOW_UP_TASKS_TO_CREATE = 1000000000;
     private final Random random = new Random();
-    private final Executor executor = new ThreadPoolExecutor(MAX_THREADPOOL_SIZE, MAX_THREADPOOL_SIZE, 1, TimeUnit.SECONDS, new LinkedBlockingQueue<Runnable>());
-    private final ConcurrentHashMap<Integer, String> mapTemporarilyHoldingGarbage = new ConcurrentHashMap<>();
+    private final ThreadPoolExecutor executor = new ThreadPoolExecutor(MAX_THREADPOOL_SIZE, MAX_THREADPOOL_SIZE, 1, TimeUnit.SECONDS, new LinkedBlockingQueue<Runnable>());
+    private final ThreadLocal<HashMap<Integer, String>> mapTemporarilyHoldingGarbage = ThreadLocal.withInitial(HashMap::new);
+    private int numberOfFollowUpTasksCreated;
     
     @Test
     public void testOutperformingTheGarbageCollector() throws InterruptedException {
-        for (int i=0; i<NUMBER_OF_OBJECTS_TO_CREATE; i++) {
+        for (int i=0; i<NUMBER_OF_OBJECTS_TO_CREATE_INITIALLY; i++) {
             executor.execute(()->produceSomeContentAndRemoveSomeOtherContent());
         }
-        logger.info("Done with producing tasks");
+        logger.info("Done with producing tasks; waiting for task queue to become empty.");
+        while (!executor.getQueue().isEmpty()) {
+            logger.info("Queue still has "+executor.getQueue().size()+" elements; still "+
+                    numberOfFollowUpTasksCreated+" follow-up tasks to produce; waiting...");
+            Thread.sleep(1000);
+        }
+        logger.info("Task queue empty; terminating");
     }
     
     private void produceSomeContentAndRemoveSomeOtherContent() {
-        mapTemporarilyHoldingGarbage.put(random.nextInt(Integer.MAX_VALUE), ""+random.nextDouble());
-        final Iterator<Entry<Integer, String>> i = mapTemporarilyHoldingGarbage.entrySet().iterator();
+        mapTemporarilyHoldingGarbage.get().put(random.nextInt(Integer.MAX_VALUE), ""+random.nextDouble());
+        final Iterator<Entry<Integer, String>> i = mapTemporarilyHoldingGarbage.get().entrySet().iterator();
         try {
             if (i.hasNext()) {
-                i.next();
-                i.remove();
+                final Entry<Integer, String> entry = i.next();
+                mapTemporarilyHoldingGarbage.get().remove(entry.getKey());
             } else {
                 logger.info("Strange; the collection is empty although we just added an element; welcome to concurrency...");
             }
         } catch (NoSuchElementException e) {
             // ignore because some other thread may already have removed the last element, and that's OK then
+            logger.log(Level.INFO, "Very strange", e);
+        }
+        if (numberOfFollowUpTasksCreated < NUMBER_OF_FOLLOW_UP_TASKS_TO_CREATE) {
+            numberOfFollowUpTasksCreated++;
+            executor.execute(()->produceSomeContentAndRemoveSomeOtherContent());
         }
     }
 }