Merge pull request #228 from AxonFramework/bugfix/shutdown-order

[#215] Fix: Reverse Component Deregistration Order in AxonServerTenantProvider

multitenancy-spring-boot-autoconfigure/src/main/java/org/axonframework/extensions/multitenancy/autoconfig/AxonServerTenantProvider.java

@@ -238,9 +238,29 @@ public void registerLifecycleHandlers(@Nonnull LifecycleRegistry lifecycle) {
         lifecycle.onShutdown(Phase.INSTRUCTION_COMPONENTS + 10, this::shutdown);
     }
 
-    private void shutdown() {
-        registrationMap.forEach((tenant, registrationList) -> {
-            registrationList.forEach(Registration::cancel);
+    /**
+     * Shuts down the AxonServerTenantProvider by deregistering all subscribed components.
+     * This method is designed to be invoked by a lifecycle handler (e.g., a shutdown hook)
+     * to ensure proper cleanup when the application is shutting down.
+     * <p>
+     * The shutdown process involves the following steps:
+     * <ol>
+     *     <li>Iterates through all registered components for each tenant.</li>
+     *     <li>Reverses the order of registrations for each tenant to ensure
+     *         last-registered components are deregistered first.</li>
+     *     <li>Invokes the cancel method on each registration, effectively
+     *         deregistering the component from the tenant.</li>
+     * </ol>
+     * <p>
+     * This method ensures that all resources associated with tenant management are properly
+     * released and that components are given the opportunity to perform any necessary cleanup
+     * in the reverse order of their registration.
+     */
+    public void shutdown() {
+        registrationMap.values().forEach(registrationList -> {
+            ArrayList<Registration> reversed = new ArrayList<>(registrationList);
+            Collections.reverse(reversed);
+            reversed.forEach(Registration::cancel);
         });
     }
 }

multitenancy-spring-boot-autoconfigure/src/test/java/org/axonframework/extensions/multitenancy/autoconfig/AxonServerTenantProviderTest.java

@@ -24,6 +24,7 @@
 import io.axoniq.axonserver.grpc.admin.ContextUpdateType;
 import io.axoniq.axonserver.grpc.admin.ReplicationGroupOverview;
 import org.axonframework.axonserver.connector.AxonServerConnectionManager;
+import org.axonframework.common.Registration;
 import org.axonframework.extensions.multitenancy.components.MultiTenantAwareComponent;
 import org.axonframework.extensions.multitenancy.components.TenantConnectPredicate;
 import org.axonframework.extensions.multitenancy.components.TenantDescriptor;
@@ -264,4 +265,40 @@ public Optional<Throwable> getError() {
             return Optional.ofNullable(error);
         }
     }
+
+    @Test
+    void whenShutdownThenDeregisterComponentsInReverseOrder() {
+        testSubject = new AxonServerTenantProvider("default, tenant-1, tenant-2",
+                tenantConnectPredicate,
+                axonServerConnectionManager);
+        testSubject.start();
+
+        MultiTenantAwareComponent component1 = mock(MultiTenantAwareComponent.class);
+        MultiTenantAwareComponent component2 = mock(MultiTenantAwareComponent.class);
+        MultiTenantAwareComponent component3 = mock(MultiTenantAwareComponent.class);
+
+        // Create mocked Registration objects
+        Registration registration1 = mock(Registration.class);
+        Registration registration2 = mock(Registration.class);
+        Registration registration3 = mock(Registration.class);
+
+        // Setup the mocks to return the registrations
+        when(component1.registerTenant(any())).thenReturn(() -> registration1.cancel());
+        when(component2.registerTenant(any())).thenReturn(() -> registration2.cancel());
+        when(component3.registerTenant(any())).thenReturn(() -> registration3.cancel());
+
+        // Subscribe components in order
+        testSubject.subscribe(component1);
+        testSubject.subscribe(component2);
+        testSubject.subscribe(component3);
+
+        // Shutdown the provider
+        testSubject.shutdown();
+
+        // Verify that cancellations happened in reverse order
+        InOrder inOrder = inOrder(registration3, registration2, registration1);
+        inOrder.verify(registration3).cancel();
+        inOrder.verify(registration2).cancel();
+        inOrder.verify(registration1).cancel();
+    }
 }