Merge pull request #484 from ekuvardin/475.SyncWriter-and-flush-problem-throwing-Exception

SyncWriter.flush() now throw Exception when previous task was failed

Author: alex268

topic/src/main/java/tech/ydb/topic/write/impl/WriterImpl.java

@@ -269,16 +269,19 @@ protected CompletableFuture<CompletableFuture<WriteAck>> sendImpl(Message messag
         return tryToEnqueue(enqueuedMessage, instant).thenApply(v -> enqueuedMessage.getFuture());
     }
 
+    /**
+     * Create a wrapper upon the future for the flush method.
+     *
+     * @return an empty Future if successful. Throw CompletionException when an error occurs.
+     */
     protected CompletableFuture<Void> flushImpl() {
         if (this.lastAcceptedMessageFuture == null) {
             return CompletableFuture.completedFuture(null);
         }
         incomingQueueLock.lock();
 
         try {
-            return this.lastAcceptedMessageFuture.isDone()
-                    ? CompletableFuture.completedFuture(null)
-                    : this.lastAcceptedMessageFuture.thenApply(v -> null);
+            return this.lastAcceptedMessageFuture.thenApply(v -> null);
         } finally {
             incomingQueueLock.unlock();
         }