fix: ability to set provider after shutdown (#556)

* fix shutdown

Signed-off-by: Kavindu Dodanduwa <kavindudodanduwa@gmail.com>

* Grammer fix for code comment 

Signed-off-by: Kavindu Dodanduwa <Kavindu-Dodan@users.noreply.github.com>

---------

Signed-off-by: Kavindu Dodanduwa <kavindudodanduwa@gmail.com>
Signed-off-by: Kavindu Dodanduwa <Kavindu-Dodan@users.noreply.github.com>

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

@@ -145,7 +145,11 @@ class EventSupport {
      * Stop the event handler task executor.
      */
     public void shutdown() {
+        try {
             taskExecutor.shutdown();
+        } catch (Exception e) {
+            log.warn("Exception while attempting to shutdown task executor", e);
+        }
     }
 
     // Handler store maintains a set of handlers for each event type.

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

@@ -21,13 +21,15 @@ import lombok.extern.slf4j.Slf4j;
 public class OpenFeatureAPI implements EventBus<OpenFeatureAPI> {
     // package-private multi-read/single-write lock
     static AutoCloseableReentrantReadWriteLock lock = new AutoCloseableReentrantReadWriteLock();
-    private EvaluationContext evaluationContext;
     private final List<Hook> apiHooks;
-    private ProviderRepository providerRepository = new ProviderRepository();
+    private ProviderRepository providerRepository;
-    private EventSupport eventSupport = new EventSupport();
+    private EventSupport eventSupport;
+    private EvaluationContext evaluationContext;
 
     protected OpenFeatureAPI() {
         apiHooks = new ArrayList<>();
+        providerRepository = new ProviderRepository();
+        eventSupport = new EventSupport();
     }
 
     private static class SingletonHolder {
@@ -190,9 +192,19 @@ public class OpenFeatureAPI implements EventBus<OpenFeatureAPI> {
         }
     }
 
+    /**
+     * Shut down and reset the current status of OpenFeature API.
+     * This call cleans up all active providers and attempts to shut down internal event handling mechanisms.
+     * Once shut down is complete, API is reset and ready to use again.
+     * */
     public void shutdown() {
+        try (AutoCloseableLock __ = lock.writeLockAutoCloseable()) {
             providerRepository.shutdown();
             eventSupport.shutdown();
+
+            providerRepository = new ProviderRepository();
+            eventSupport = new EventSupport();
+        }
     }
 
     /**
@@ -264,15 +276,6 @@ public class OpenFeatureAPI implements EventBus<OpenFeatureAPI> {
         }
     }
 
-    /**
-     * This method is only here for testing as otherwise all tests after the API
-     * shutdown test would fail.
-     */
-    final void reset() {
-        providerRepository = new ProviderRepository();
-        eventSupport = new EventSupport();
-    }
-
     /**
      * Runs the handlers associated with a particular provider.
      * 

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

@@ -109,9 +109,22 @@ class ShutdownBehaviorSpecTest {
                             verify(defaultProvider).shutdown();
                             verify(namedProvider).shutdown();
                         });
+            }
+        }
 
-                api.reset();
+
-            }
+        @Test
+        @DisplayName("once shutdown is complete, api must be ready to use again")
+        void apiIsReadyToUseAfterShutdown() {
+            final OpenFeatureAPI openFeatureAPI = OpenFeatureAPI.getInstance();
+
+            NoOpProvider p1 = new NoOpProvider();
+            openFeatureAPI.setProvider(p1);
+
+            openFeatureAPI.shutdown();
+
+            NoOpProvider p2 = new NoOpProvider();
+            openFeatureAPI.setProvider(p2);
         }
     }
 }