Add `flush` method for BulkProcessor class

There is no explicit method `flush/execute` in `BulkProcessor` class. This can be useful in certain scenarios.
Currently it requires to close and create a new BulkProcessor if one wants an immediate flush.

Closes #5575.
Closes #5570.

src/main/java/org/elasticsearch/action/bulk/BulkProcessor.java

@@ -33,6 +33,7 @@ import org.elasticsearch.common.unit.ByteSizeValue;
 import org.elasticsearch.common.unit.TimeValue;
 import org.elasticsearch.common.util.concurrent.EsExecutors;
 
+import java.io.Closeable;
 import java.util.concurrent.*;
 import java.util.concurrent.atomic.AtomicLong;
 
@@ -43,7 +44,7 @@ import java.util.concurrent.atomic.AtomicLong;
  * <p/>
  * In order to create a new bulk processor, use the {@link Builder}.
  */
-public class BulkProcessor {
+public class BulkProcessor implements Closeable {
 
     /**
      * A listener for the execution.
@@ -191,6 +192,7 @@ public class BulkProcessor {
         }
     }
 
+    @Override
     /**
      * Closes the processor. If flushing by time is enabled, then its shutdown. Any remaining bulk actions are flushed.
      */
@@ -235,7 +237,14 @@ public class BulkProcessor {
         return this;
     }
 
+    public void ensureOpen() {
+        if (closed) {
+            throw new ElasticsearchIllegalStateException("bulk process already closed");
+        }
+    }
+
     private synchronized void internalAdd(ActionRequest request, @Nullable Object payload) {
+        ensureOpen();
         bulkRequest.add(request, payload);
         executeIfNeeded();
     }
@@ -251,9 +260,7 @@ public class BulkProcessor {
     }
 
     private void executeIfNeeded() {
-        if (closed) {
+        ensureOpen();
-            throw new ElasticsearchIllegalStateException("bulk process already closed");
-        }
         if (!isOverTheLimit()) {
             return;
         }
@@ -322,6 +329,16 @@ public class BulkProcessor {
         return false;
     }
 
+    /**
+     * Flush pending delete or index requests.
+     */
+    public synchronized void flush() {
+        ensureOpen();
+        if (bulkRequest.numberOfActions() > 0) {
+            execute();
+        }
+    }
+
     class Flush implements Runnable {
 
         @Override

src/test/java/org/elasticsearch/document/BulkTests.java

@@ -587,9 +587,8 @@ public class BulkTests extends ElasticsearchIntegrationTest {
             public void afterBulk(long executionId, BulkRequest request, Throwable failure) {}
         };
 
-        BulkProcessor processor = null;
+        try (BulkProcessor processor = BulkProcessor.builder(client(), listener).setBulkActions(5)
-        try {
+                                        .setConcurrentRequests(1).setName("foo").build()) {
-            processor = BulkProcessor.builder(client(), listener).setBulkActions(5).setConcurrentRequests(1).setName("foo").build();
             Map<String, Object> data = Maps.newHashMap();
             data.put("foo", "bar");
 
@@ -602,10 +601,6 @@ public class BulkTests extends ElasticsearchIntegrationTest {
             BulkResponse response = responseQueue.poll(5, TimeUnit.SECONDS);
             assertThat("Could not get a bulk response in 5 seconds", response, is(notNullValue()));
             assertThat(response.getItems().length, is(5));
-        } finally {
-            if (processor != null) {
-                processor.close();
-            }
         }
     }
 
@@ -626,4 +621,40 @@ public class BulkTests extends ElasticsearchIntegrationTest {
             assertThat(bulkResponse.getItems()[i].isFailed(), is(expectedFailures[i]));
         }
     }
+
+    @Test
+    public void testBulkProcessorFlush() throws InterruptedException {
+        final BlockingQueue<BulkResponse> responseQueue = new SynchronousQueue();
+
+        BulkProcessor.Listener listener = new BulkProcessor.Listener() {
+            @Override
+            public void beforeBulk(long executionId, BulkRequest request) {}
+
+            @Override
+            public void afterBulk(long executionId, BulkRequest request, BulkResponse response) {
+                responseQueue.add(response);
+            }
+
+            @Override
+            public void afterBulk(long executionId, BulkRequest request, Throwable failure) {}
+        };
+
+        try (BulkProcessor processor = BulkProcessor.builder(client(), listener).setBulkActions(6)
+                                        .setConcurrentRequests(1).setName("foo").build()) {
+            Map<String, Object> data = Maps.newHashMap();
+            data.put("foo", "bar");
+
+            processor.add(new IndexRequest("test", "test", "1").source(data));
+            processor.add(new IndexRequest("test", "test", "2").source(data));
+            processor.add(new IndexRequest("test", "test", "3").source(data));
+            processor.add(new IndexRequest("test", "test", "4").source(data));
+            processor.add(new IndexRequest("test", "test", "5").source(data));
+
+            processor.flush();
+
+            BulkResponse response = responseQueue.poll(1, TimeUnit.SECONDS);
+            assertThat("Could not get a bulk response even after an explicit flush.", response, is(notNullValue()));
+            assertThat(response.getItems().length, is(5));
+        }
+    }
 }