chore: suggestions to the fix (#325)

Author: gastonfournier

src/main/java/io/getunleash/util/UnleashScheduledExecutorImpl.java

@@ -54,15 +54,17 @@ public Future<Void> scheduleOnce(Runnable runnable) {
     }
 
     @Override
-    public void shutdown() {
+    public synchronized void shutdown() {
         this.scheduledThreadPoolExecutor.shutdown();
+        this.executorService.shutdown();
         INSTANCE = null;
         LOG.info("Shutdown - Scheduled Executor");
     }
 
     @Override
-    public void shutdownNow() {
+    public synchronized void shutdownNow() {
         this.scheduledThreadPoolExecutor.shutdownNow();
+        this.executorService.shutdownNow();
         INSTANCE = null;
         LOG.info("Shutdown Now - Scheduled Executor");
     }

src/test/java/io/getunleash/HotReloadSchedulerReuseTest.java

@@ -0,0 +1,72 @@
+package io.getunleash;
+
+import io.getunleash.util.UnleashConfig;
+import org.junit.jupiter.api.*;
+
+import java.lang.reflect.Field;
+import java.util.concurrent.ScheduledThreadPoolExecutor;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+class HotReloadSchedulerReuseTest {
+
+
+    private UnleashConfig baseConfig() {
+        return UnleashConfig.builder()
+            .appName("hot-reload-test-app")
+            .instanceId("A")
+            .unleashAPI("http://localhost")    // never hit
+            .synchronousFetchOnInitialisation(false)
+            .fetchTogglesInterval(100)
+            .sendMetricsInterval(100)
+            .build();
+    }
+
+    private ScheduledThreadPoolExecutor currentGlobalExecutor() throws Exception {
+        Class<?> execClazz = Class.forName("io.getunleash.util.UnleashScheduledExecutorImpl");
+        Field instance = execClazz.getDeclaredField("INSTANCE");
+        instance.setAccessible(true);
+        Object inst = instance.get(null);
+        if (inst == null) return null;
+
+        Field pool = execClazz.getDeclaredField("scheduledThreadPoolExecutor");
+        pool.setAccessible(true);
+        return (ScheduledThreadPoolExecutor) pool.get(inst);
+    }
+
+    @Test
+    void secondClientDoesNotReuseSchedulerExecutor() throws Exception {
+        // 1) Create first client; let it schedule background tasks
+        DefaultUnleash first = new DefaultUnleash(
+            baseConfig()
+        );
+
+        // Let it initialize/schedule
+        Thread.sleep(150);
+
+        // Snapshot the global executor
+        ScheduledThreadPoolExecutor execBeforeShutdown = currentGlobalExecutor();
+        assertThat(execBeforeShutdown).isNotNull();
+        assertThat(execBeforeShutdown.isShutdown()).isFalse();
+
+        // 2) Simulate app stop (DevTools restart) by shutting the client
+        first.shutdown();
+
+        // After shutdown, the global executor instance is properly reset to null
+        ScheduledThreadPoolExecutor execAfterShutdown = currentGlobalExecutor();
+        assertThat(execAfterShutdown).isNull();
+
+        // 3) "Reloaded app": create a second client in the same JVM (statics still around)
+        DefaultUnleash second = new DefaultUnleash(
+            baseConfig()
+        );
+
+        // 4) Assert that the second client creates a fresh executor (not reusing the terminated one)
+        ScheduledThreadPoolExecutor execUsedBySecond = currentGlobalExecutor();
+        assertThat(execUsedBySecond).isNotNull();
+        assertThat(execUsedBySecond.isShutdown()).isFalse(); // it's a new one
+
+        // Clean up
+        second.shutdown();
+    }
+}