Addressing bulk ingester stuck threads (#870)

* signaling after successfully adding

* stress test unit test

* removed memory calc

java-client/src/main/java/co/elastic/clients/elasticsearch/_helpers/bulk/BulkIngester.java

@@ -358,6 +358,9 @@ public void add(BulkOperation operation, Context context) {
             if (!canAddOperation()) {
                 flush();
             }
+            else {
+                addCondition.signalIfReady();
+            }
         });
     }
 

java-client/src/test/java/co/elastic/clients/elasticsearch/_helpers/bulk/BulkIngesterTest.java

@@ -28,6 +28,7 @@
 import co.elastic.clients.elasticsearch.core.bulk.BulkResponseItem;
 import co.elastic.clients.elasticsearch.core.bulk.OperationType;
 import co.elastic.clients.elasticsearch.end_to_end.RequestTest;
+import co.elastic.clients.elasticsearch.indices.IndicesStatsResponse;
 import co.elastic.clients.json.JsonpMapper;
 import co.elastic.clients.json.SimpleJsonpMapper;
 import co.elastic.clients.transport.ElasticsearchTransport;
@@ -146,6 +147,50 @@ private void multiThreadTest(int maxOperations, int maxRequests, int numThreads,
         assertEquals(expectedRequests, transport.requestsStarted.get());
     }
 
+    @Test
+    public void multiThreadStressTest() throws InterruptedException, IOException {
+
+        String index = "bulk-ingester-stress-test";
+        ElasticsearchClient client = ElasticsearchTestServer.global().client();
+
+        // DISCLAIMER: this configuration is highly inefficient and only used here to showcase an extreme
+        // situation where the number of adding threads greatly exceeds the number of concurrent requests
+        // handled by the ingester. It's strongly recommended to always tweak maxConcurrentRequests accordingly.
+        BulkIngester<?> ingester = BulkIngester.of(b -> b
+                .client(client)
+                .globalSettings(s -> s.index(index))
+                .flushInterval(5, TimeUnit.SECONDS)
+        );
+
+        RequestTest.AppData appData = new RequestTest.AppData();
+        appData.setIntValue(42);
+        appData.setMsg("Some message");
+
+        ExecutorService executor = Executors.newFixedThreadPool(50);
+
+        for (int i = 0; i < 100000; i++) {
+            int ii = i;
+            Runnable thread = () -> {
+                int finalI = ii;
+                ingester.add(_1 -> _1
+                    .create(_2 -> _2
+                        .id(String.valueOf(finalI))
+                        .document(appData)
+                    ));
+            };
+            executor.submit(thread);
+        }
+
+        executor.awaitTermination(10,TimeUnit.SECONDS);
+        ingester.close();
+
+        client.indices().refresh();
+
+        IndicesStatsResponse indexStats = client.indices().stats(g -> g.index(index));
+
+        assertTrue(indexStats.indices().get(index).primaries().docs().count()==100000);
+    }
+
     @Test
     public void sizeLimitTest() throws Exception {
         TestTransport transport = new TestTransport();