Fix flaky optional_spec111 TCK multicast test

The test subscribes 3 subscribers to the same publisher and asserts all receive elements in the same order. With a new single-thread executor per mapping call, each CF ran on its own thread, making delivery order depend on thread scheduling. Sometimes elements arrived in order (test passed), sometimes not (assertion failed, caught by TCK, converted to skip). Use a shared single-thread executor per publisher (matching the pattern already used by the Ordered publisher variants) so CFs complete sequentially in submission order. The test now deterministically passes. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
andimarek · Mar 6, 2026 · Mar 6, 2026 · Mar 6, 2026 · Mar 6, 2026 · Mar 6, 2026
commit 4936a15a319bd8b5b2ca4c5172ffedc89567a65e
diff --git a/...cution/reactive/tck/CompletionStageMappingPublisherRandomCompleteTckVerificationTest.java b/...cution/reactive/tck/CompletionStageMappingPublisherRandomCompleteTckVerificationTest.java
@@ -12,6 +12,7 @@
 import java.util.Random;
 import java.util.concurrent.CompletableFuture;
 import java.util.concurrent.CompletionStage;
+import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Executors;
 import java.util.function.Function;
 
@@ -50,6 +51,7 @@ public boolean skipStochasticTests() {
 
     @NonNull
     private static Function<Integer, CompletionStage<String>> mapperFunc() {
+        ExecutorService executor = Executors.newSingleThreadExecutor();
         return i -> CompletableFuture.supplyAsync(() -> {
             int ms = rand(0, 5);
             try {
@@ -58,7 +60,7 @@ private static Function<Integer, CompletionStage<String>> mapperFunc() {
                 throw new RuntimeException(e);
             }
             return i + "!";
-        }, Executors.newSingleThreadExecutor());
+        }, executor);
     }
 
     static Random rn = new Random();

diff --git a/...vy/graphql/execution/reactive/tck/CompletionStageMappingPublisherTckVerificationTest.java b/...vy/graphql/execution/reactive/tck/CompletionStageMappingPublisherTckVerificationTest.java
@@ -10,6 +10,7 @@
 import java.time.Duration;
 import java.util.concurrent.CompletableFuture;
 import java.util.concurrent.CompletionStage;
+import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Executors;
 import java.util.function.Function;
 
@@ -32,14 +33,16 @@ public long maxElementsFromPublisher() {
     @Override
     public Publisher<String> createPublisher(long elements) {
         Publisher<Integer> publisher = Flowable.range(0, (int) elements);
-        Function<Integer, CompletionStage<String>> mapper = i -> CompletableFuture.supplyAsync(() -> i + "!", Executors.newSingleThreadExecutor());
+        ExecutorService executor = Executors.newSingleThreadExecutor();
+        Function<Integer, CompletionStage<String>> mapper = i -> CompletableFuture.supplyAsync(() -> i + "!", executor);
         return new CompletionStageMappingPublisher<>(publisher, mapper);
     }
 
     @Override
     public Publisher<String> createFailedPublisher() {
         Publisher<Integer> publisher = Flowable.error(() -> new RuntimeException("Bang"));
-        Function<Integer, CompletionStage<String>> mapper = i -> CompletableFuture.supplyAsync(() -> i + "!", Executors.newSingleThreadExecutor());
+        ExecutorService executor = Executors.newSingleThreadExecutor();
+        Function<Integer, CompletionStage<String>> mapper = i -> CompletableFuture.supplyAsync(() -> i + "!", executor);
         return new CompletionStageMappingPublisher<>(publisher, mapper);
     }