From 3510956935745871a7774628265b7b9492f6c155 Mon Sep 17 00:00:00 2001
From: jonmv <venstad@gmail.com>
Date: Fri, 13 Oct 2023 18:36:41 +0200
Subject: Fix test to fail when sequenced-task discards it on destroy()

---
 .../java/com/yahoo/messagebus/SequencerTestCase.java  | 19 +++++++++++++------
 1 file changed, 13 insertions(+), 6 deletions(-)

(limited to 'messagebus/src')

diff --git a/messagebus/src/test/java/com/yahoo/messagebus/SequencerTestCase.java b/messagebus/src/test/java/com/yahoo/messagebus/SequencerTestCase.java
index 493afe4f12d..e13d370fe8c 100644
--- a/messagebus/src/test/java/com/yahoo/messagebus/SequencerTestCase.java
+++ b/messagebus/src/test/java/com/yahoo/messagebus/SequencerTestCase.java
@@ -9,6 +9,8 @@ import java.util.Queue;
 import java.util.Set;
 import java.util.concurrent.ConcurrentLinkedQueue;
 import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.Executor;
+import java.util.concurrent.Executors;
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.atomic.AtomicReference;
 
@@ -115,11 +117,16 @@ public class SequencerTestCase {
         int n = 10000;
         CountDownLatch latch = new CountDownLatch(n);
         AtomicReference<Reply> waiting = new AtomicReference<>();
+        Executor executor = Executors.newSingleThreadExecutor();
         MessageHandler sender = message -> {
-            Reply reply = new EmptyReply();
-            reply.swapState(message);
-            reply.setMessage(message);
-            if ( ! waiting.compareAndSet(null, reply)) reply.popHandler().handleReply(reply);
+            Runnable task = () -> {
+                Reply reply = new EmptyReply();
+                reply.swapState(message);
+                reply.setMessage(message);
+                if ( ! waiting.compareAndSet(null, reply)) reply.popHandler().handleReply(reply);
+            };
+            if (Math.random() < 0.5) executor.execute(task); // Usually, RPC thread runs this.
+            else task.run();                                 // But on, e.g., timeouts, it runs in the caller thread instead.
         };
 
         Queue<Message> answered = new ConcurrentLinkedQueue<>();
@@ -130,7 +137,7 @@ public class SequencerTestCase {
 
         Messenger messenger = new Messenger();
         messenger.start();
-        Sequencer sequencer = new Sequencer(sender, messenger);
+        Sequencer sequencer = new Sequencer(sender, messenger); // Not using the messenger results in a stack overflow error.
 
         Queue<Message> sent = new ConcurrentLinkedQueue<>();
         for (int i = 0; i < 10000; i++) {
@@ -142,7 +149,7 @@ public class SequencerTestCase {
 
         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, ...
+        assertEquals(Set.copyOf(sent), Set.copyOf(answered)); // Order is not guaranteed at all!
         messenger.destroy();
     }
 
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