fix: allow for providers to safely shutdown

Signed-off-by: Nicklas Lundin <nicklasl@spotify.com>

Author: nicklasl

src/main/java/dev/openfeature/sdk/ProviderRepository.java

@@ -10,6 +10,7 @@
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Executors;
+import java.util.concurrent.TimeUnit;
 import java.util.concurrent.atomic.AtomicReference;
 import java.util.function.BiConsumer;
 import java.util.function.Consumer;
@@ -277,5 +278,14 @@ public void shutdown() {
                 .forEach(this::shutdownProvider);
         this.stateManagers.clear();
         taskExecutor.shutdown();
+        try {
+            if (!taskExecutor.awaitTermination(3, TimeUnit.SECONDS)) {
+                log.warn("Task executor did not terminate before the timeout period had elapsed");
+                taskExecutor.shutdownNow();
+            }
+        } catch (InterruptedException e) {
+            taskExecutor.shutdownNow();
+            Thread.currentThread().interrupt();
+        }
     }
 }

src/test/java/dev/openfeature/sdk/ProviderRepositoryTest.java

@@ -15,6 +15,7 @@
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Executors;
 import java.util.concurrent.Future;
+import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.function.BiConsumer;
 import java.util.function.Consumer;
 import java.util.function.Function;
@@ -289,6 +290,78 @@ void shouldRunLambdasOnError() throws Exception {
                 verify(afterError, timeout(TIMEOUT)).accept(eq(errorFeatureProvider), any());
             }
         }
+
+        @Nested
+        class GracefulShutdownBehavior {
+
+            @Test
+            @DisplayName("should complete shutdown successfully when executor terminates within timeout")
+            void shouldCompleteShutdownSuccessfullyWhenExecutorTerminatesWithinTimeout() {
+                FeatureProvider provider = createMockedProvider();
+                setFeatureProvider(provider);
+
+                assertThatCode(() -> providerRepository.shutdown()).doesNotThrowAnyException();
+
+                verify(provider, timeout(TIMEOUT)).shutdown();
+            }
+
+            @Test
+            @DisplayName("should force shutdown when executor does not terminate within timeout")
+            void shouldForceShutdownWhenExecutorDoesNotTerminateWithinTimeout() throws Exception {
+                FeatureProvider provider = createMockedProvider();
+                AtomicBoolean wasInterrupted = new AtomicBoolean(false);
+                doAnswer(invocation -> {
+                    try {
+                        Thread.sleep(TIMEOUT);
+                    } catch (InterruptedException e) {
+                        wasInterrupted.set(true);
+                        throw e;
+                    }
+                    return null;
+                }).when(provider).shutdown();
+
+                setFeatureProvider(provider);
+
+                assertThatCode(() -> providerRepository.shutdown()).doesNotThrowAnyException();
+
+                verify(provider, timeout(TIMEOUT)).shutdown();
+                // Verify that shutdownNow() interrupted the running shutdown task
+                await().atMost(Duration.ofSeconds(1))
+                        .untilAsserted(() -> assertThat(wasInterrupted.get()).isTrue());
+            }
+
+            @Test
+            @DisplayName("should handle interruption during shutdown gracefully")
+            void shouldHandleInterruptionDuringShutdownGracefully() throws Exception {
+                FeatureProvider provider = createMockedProvider();
+                setFeatureProvider(provider);
+
+                Thread shutdownThread = new Thread(() -> {
+                    providerRepository.shutdown();
+                });
+
+                shutdownThread.start();
+                shutdownThread.interrupt();
+                shutdownThread.join(TIMEOUT);
+
+                assertThat(shutdownThread.isAlive()).isFalse();
+                verify(provider, timeout(TIMEOUT)).shutdown();
+            }
+
+            @Test
+            @DisplayName("should not hang indefinitely on shutdown")
+            void shouldNotHangIndefinitelyOnShutdown() {
+                FeatureProvider provider = createMockedProvider();
+                setFeatureProvider(provider);
+
+                await().alias("shutdown should complete within reasonable time")
+                        .atMost(Duration.ofSeconds(5))
+                        .until(() -> {
+                            providerRepository.shutdown();
+                            return true;
+                        });
+            }
+        }
     }
 
     @Test