From 6606a8d38c25db4180317cb7aa31fa5b9b5c4815 Mon Sep 17 00:00:00 2001
From: jonmv <venstad@gmail.com>
Date: Fri, 13 Oct 2023 17:25:45 +0200
Subject: Test sequencer with messenger and deep reply->send-next recursion

---
 .../main/java/com/yahoo/messagebus/Sequencer.java  |  2 +-
 .../com/yahoo/messagebus/SequencerTestCase.java    | 46 +++++++++++++++++++++-
 2 files changed, 46 insertions(+), 2 deletions(-)

(limited to 'messagebus/src')

diff --git a/messagebus/src/main/java/com/yahoo/messagebus/Sequencer.java b/messagebus/src/main/java/com/yahoo/messagebus/Sequencer.java
index 2244559b54a..05e71e0f006 100644
--- a/messagebus/src/main/java/com/yahoo/messagebus/Sequencer.java
+++ b/messagebus/src/main/java/com/yahoo/messagebus/Sequencer.java
@@ -148,7 +148,7 @@ public class Sequencer implements MessageHandler, ReplyHandler {
         private final Message msg;
         SequencedSendTask(Message msg) { this.msg = msg; }
         @Override public void run() { sequencedSend(msg); }
-        @Override public void destroy() { msg.discard(); }
+        @Override public void destroy() { }
     }
 
     private void sendNextInSequence(long seqId) {
diff --git a/messagebus/src/test/java/com/yahoo/messagebus/SequencerTestCase.java b/messagebus/src/test/java/com/yahoo/messagebus/SequencerTestCase.java
index f06ff4f5f73..493afe4f12d 100644
--- a/messagebus/src/test/java/com/yahoo/messagebus/SequencerTestCase.java
+++ b/messagebus/src/test/java/com/yahoo/messagebus/SequencerTestCase.java
@@ -6,8 +6,15 @@ import org.junit.jupiter.api.Test;
 
 import java.util.LinkedList;
 import java.util.Queue;
+import java.util.Set;
+import java.util.concurrent.ConcurrentLinkedQueue;
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicReference;
 
-import static org.junit.jupiter.api.Assertions.*;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertTrue;
 
 /**
  * @author Simon Thoresen Hult
@@ -102,6 +109,43 @@ public class SequencerTestCase {
         assertEquals(0, dst.size());
     }
 
+    @Test
+    void testRecursiveSending() throws InterruptedException {
+        // This test queues up a lot of replies, and then has them all ready to return at once.
+        int n = 10000;
+        CountDownLatch latch = new CountDownLatch(n);
+        AtomicReference<Reply> waiting = new AtomicReference<>();
+        MessageHandler sender = message -> {
+            Reply reply = new EmptyReply();
+            reply.swapState(message);
+            reply.setMessage(message);
+            if ( ! waiting.compareAndSet(null, reply)) reply.popHandler().handleReply(reply);
+        };
+
+        Queue<Message> answered = new ConcurrentLinkedQueue<>();
+        ReplyHandler handler = reply -> {
+            answered.add(reply.getMessage());
+            latch.countDown();
+        };
+
+        Messenger messenger = new Messenger();
+        messenger.start();
+        Sequencer sequencer = new Sequencer(sender, messenger);
+
+        Queue<Message> sent = new ConcurrentLinkedQueue<>();
+        for (int i = 0; i < 10000; i++) {
+            Message message = new MyMessage(true, 1);
+            message.pushHandler(handler);
+            sequencer.handleMessage(message);
+            sent.add(message);
+        }
+
+        waiting.get().popHandler().handleReply(waiting.get());
+        assertTrue(latch.await(10, TimeUnit.SECONDS), "All messages should obtain a reply within 10s");
+        assertEquals(Set.copyOf(sent), Set.copyOf(answered)); // Order is not guaranteed, but typically something like 2, 1, 4, 3, 6, 5, ...
+        messenger.destroy();
+    }
+
     private static class TestQueue extends LinkedList<Routable> implements ReplyHandler {
 
         void checkReply(boolean hasSeqId, long seqId) {
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