From 91b722019d46d265ad6dde4c8d3a64b791902843 Mon Sep 17 00:00:00 2001
From: Vasiliy Mikhailov <vasiliy.mikhailov@gmail.com>
Date: Mon, 22 Jun 2026 21:18:56 +0300
Subject: [PATCH] Fix IllegalStateException in
 SchedulerToExecutorService.invokeAny

invokeAny() guarded its result check with f.exceptionNow() == null, but
Future.exceptionNow() throws IllegalStateException when the task completed
normally (i.e. there is no exception), per its contract. As a result the
first successfully completed task triggers an IllegalStateException instead
of being returned. Both invokeAny overloads are affected.

Replace the isDone/isCancelled/exceptionNow probe with a direct
Future.State.SUCCESS check, which is the intended state query and does not
throw.
---
 .../SchedulerToExecutorService.java           |  4 +-
 .../SchedulerToExecutorServiceTest.java       | 72 +++++++++++++++++++
 2 files changed, 74 insertions(+), 2 deletions(-)
 create mode 100644 src/test/java/io/reactivex/rxjava4/internal/schedulers/SchedulerToExecutorServiceTest.java

diff --git a/src/main/java/io/reactivex/rxjava4/internal/schedulers/SchedulerToExecutorService.java b/src/main/java/io/reactivex/rxjava4/internal/schedulers/SchedulerToExecutorService.java
index 729e0604fbd..5449901fab8 100644
--- a/src/main/java/io/reactivex/rxjava4/internal/schedulers/SchedulerToExecutorService.java
+++ b/src/main/java/io/reactivex/rxjava4/internal/schedulers/SchedulerToExecutorService.java
@@ -189,7 +189,7 @@ public <T> T invokeAny(Collection<? extends Callable<T>> tasks) throws Interrupt
 
         while (!isTerminated()) {
             for (var f : result) {
-                if (f.isDone() && !f.isCancelled() && f.exceptionNow() == null) {
+                if (f.state() == Future.State.SUCCESS) {
 
                     var v = f.resultNow();
 
@@ -224,7 +224,7 @@ public <T> T invokeAny(Collection<? extends Callable<T>> tasks, long timeout, Ti
             totalTime--;
 
             for (var f : result) {
-                if (f.isDone() && !f.isCancelled() && f.exceptionNow() == null) {
+                if (f.state() == Future.State.SUCCESS) {
 
                     var v = f.resultNow();
 
diff --git a/src/test/java/io/reactivex/rxjava4/internal/schedulers/SchedulerToExecutorServiceTest.java b/src/test/java/io/reactivex/rxjava4/internal/schedulers/SchedulerToExecutorServiceTest.java
new file mode 100644
index 00000000000..a5493e1ffc5
--- /dev/null
+++ b/src/test/java/io/reactivex/rxjava4/internal/schedulers/SchedulerToExecutorServiceTest.java
@@ -0,0 +1,72 @@
+/*
+ * Copyright (c) 2016-present, RxJava Contributors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in
+ * compliance with the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software distributed under the License is
+ * distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See
+ * the License for the specific language governing permissions and limitations under the License.
+ */
+
+package io.reactivex.rxjava4.internal.schedulers;
+
+import static org.junit.Assert.*;
+
+import java.util.Arrays;
+import java.util.concurrent.*;
+import java.util.concurrent.atomic.AtomicReference;
+
+import org.junit.Test;
+
+import io.reactivex.rxjava4.core.Scheduler;
+import io.reactivex.rxjava4.disposables.Disposable;
+import io.reactivex.rxjava4.schedulers.Schedulers;
+
+public class SchedulerToExecutorServiceTest {
+
+    @Test
+    public void invokeAnyShouldReturnResultOfCompletedTask() throws Exception {
+        Scheduler scheduler = Schedulers.trampoline();
+        SchedulerToExecutorService executor = new SchedulerToExecutorService(
+                scheduler, new AtomicReference<>(null));
+
+        Callable<String> task1 = () -> "result1";
+        Callable<String> task2 = () -> "result2";
+
+        String result = executor.invokeAny(Arrays.asList(task1, task2));
+
+        assertNotNull("invokeAny should return a result", result);
+        assertTrue("result should be one of the task results",
+                result.equals("result1") || result.equals("result2"));
+    }
+
+    @Test
+    public void invokeAnyWithSingleTask() throws Exception {
+        Scheduler scheduler = Schedulers.trampoline();
+        SchedulerToExecutorService executor = new SchedulerToExecutorService(
+                scheduler, new AtomicReference<>(null));
+
+        Callable<Integer> task = () -> 42;
+
+        Integer result = executor.invokeAny(Arrays.asList(task));
+
+        assertEquals("invokeAny should return the single task result", Integer.valueOf(42), result);
+    }
+
+    @Test
+    public void invokeAnyWithEmptyTasksShouldThrow() throws Exception {
+        Scheduler scheduler = Schedulers.trampoline();
+        SchedulerToExecutorService executor = new SchedulerToExecutorService(
+                scheduler, new AtomicReference<>(null));
+
+        try {
+            executor.invokeAny(Arrays.asList());
+            fail("invokeAny with empty tasks should throw IllegalArgumentException");
+        } catch (IllegalArgumentException expected) {
+            // expected
+        }
+    }
+}