add several code comments and apply review comments

core/src/test/java/org/elasticsearch/action/admin/indices/create/CreateIndexIT.java

@@ -208,14 +208,15 @@ public class CreateIndexIT extends ESIntegTestCase {
 
     public void testCreateAndDeleteIndexConcurrently() throws InterruptedException {
         createIndex("test");
-        final AtomicInteger indexDeleteAction = new AtomicInteger(0);
+        final AtomicInteger indexVersion = new AtomicInteger(0);
+        final Object indexVersionLock = new Object();
         final CountDownLatch latch = new CountDownLatch(1);
         int numDocs = randomIntBetween(1, 10);
         for (int i = 0; i < numDocs; i++) {
-            client().prepareIndex("test", "test").setSource("index_version", indexDeleteAction.get()).get();
+            client().prepareIndex("test", "test").setSource("index_version", indexVersion.get()).get();
         }
-        synchronized (indexDeleteAction) { // not necessarily needed here
-            indexDeleteAction.incrementAndGet();
+        synchronized (indexVersionLock) { // not necessarily needed here but for completeness we lock here too
+            indexVersion.incrementAndGet();
         }
         client().admin().indices().prepareDelete("test").execute(new ActionListener<DeleteIndexResponse>() { // this happens async!!!
                 @Override
@@ -223,11 +224,13 @@ public class CreateIndexIT extends ESIntegTestCase {
                     Thread thread = new Thread() {
                      public void run() {
                          try {
-                             client().prepareIndex("test", "test").setSource("index_version", indexDeleteAction.get()).get(); // recreate that index
-                             synchronized (indexDeleteAction) {
-                                 indexDeleteAction.incrementAndGet();
+                             client().prepareIndex("test", "test").setSource("index_version", indexVersion.get()).get(); // recreate that index
+                             synchronized (indexVersionLock) {
+                                 // we sync here since we have to ensure that all indexing operations below for a given ID are done before we increment the
+                                 // index version otherwise a doc that is in-flight could make it into an index that it was supposed to be deleted for and our assertion fail...
+                                 indexVersion.incrementAndGet();
                              }
-                             client().admin().indices().prepareDelete("test").get(); // from here on all docs with index_version == 0|1 must be gone!!!! only 2 are ok;
+                             assertAcked(client().admin().indices().prepareDelete("test").get()); // from here on all docs with index_version == 0|1 must be gone!!!! only 2 are ok;
                          } finally {
                              latch.countDown();
                          }
@@ -238,15 +241,15 @@ public class CreateIndexIT extends ESIntegTestCase {
 
                 @Override
                 public void onFailure(Throwable e) {
-                 ExceptionsHelper.reThrowIfNotNull(e);
+                    throw new RuntimeException(e);
                 }
             }
         );
         numDocs = randomIntBetween(100, 200);
         for (int i = 0; i < numDocs; i++) {
             try {
-                synchronized (indexDeleteAction) {
-                    client().prepareIndex("test", "test").setSource("index_version", indexDeleteAction.get()).get();
+                synchronized (indexVersionLock) {
+                    client().prepareIndex("test", "test").setSource("index_version", indexVersion.get()).get();
                 }
             } catch (IndexNotFoundException inf) {
                 // fine
@@ -254,10 +257,11 @@ public class CreateIndexIT extends ESIntegTestCase {
         }
         latch.await();
         refresh();
-        SearchResponse expected = client().prepareSearch("test").setIndicesOptions(IndicesOptions.lenientExpandOpen()).setQuery(new RangeQueryBuilder("index_version").from(indexDeleteAction.get(), true)).get();
+
+        // we only really assert that we never reuse segments of old indices or anything like this here and that nothing fails with crazy exceptions
+        SearchResponse expected = client().prepareSearch("test").setIndicesOptions(IndicesOptions.lenientExpandOpen()).setQuery(new RangeQueryBuilder("index_version").from(indexVersion.get(), true)).get();
         SearchResponse all = client().prepareSearch("test").setIndicesOptions(IndicesOptions.lenientExpandOpen()).get();
-        assertEquals(expected + " vs. " + all, expected.getHits().getTotalHits(), all.getHits().getTotalHits()
-        );
+        assertEquals(expected + " vs. " + all, expected.getHits().getTotalHits(), all.getHits().getTotalHits());
         logger.info("total: {}", expected.getHits().getTotalHits());
     }