Workaround for shutdown error (#722)

This commit is a workaround for an error which seems to happen since
the upgrade to Micronaut 4.6. In a nutshell, when the `/stop` endpoint
is called, the thread which was started to monitor if the service is
properly shutdown after a timeout was started and the application
context was closed, _before_ the `stop` method would return something
to the client. As a consequence, there was an error message saying
that the application context wasn't open and that a bean (the message
writers) weren't found. This was not quite true, since the application
context _used to be_ open but wasn't.

The workaround, which isn't great, is to use the task scheduler to
delay the shutdown by a few hundreds of milliseconds. This gives the
opportunity to send the response back to the client _before_ the
application context is shutdown.

Note that in any case, this wasn't a big issue, since the service
would be shutdown anyway, but the error message for the user wasn't
great.

test-resources-server/src/main/java/io/micronaut/testresources/server/TestResourcesController.java

@@ -22,6 +22,7 @@
 import io.micronaut.http.annotation.Post;
 import io.micronaut.runtime.server.EmbeddedServer;
 import io.micronaut.scheduling.TaskExecutors;
+import io.micronaut.scheduling.TaskScheduler;
 import io.micronaut.scheduling.annotation.ExecuteOn;
 import io.micronaut.testresources.core.ResolverLoader;
 import io.micronaut.testresources.core.TestResourcesResolutionException;
@@ -33,6 +34,7 @@
 
 import java.io.Closeable;
 import java.io.IOException;
+import java.time.Duration;
 import java.util.Collection;
 import java.util.Collections;
 import java.util.List;
@@ -57,15 +59,18 @@ public class TestResourcesController implements TestResourcesResolver {
     private final List<PropertyResolutionListener> propertyResolutionListeners;
     private final EmbeddedServer embeddedServer;
     private final ApplicationContext applicationContext;
+    private final TaskScheduler taskScheduler;
 
     public TestResourcesController(List<PropertyResolutionListener> propertyResolutionListeners,
                                    EmbeddedServer embeddedServer,
                                    ApplicationContext applicationContext,
-                                   ResolverLoader loader) {
+                                   ResolverLoader loader,
+                                   TaskScheduler taskScheduler) {
         this.propertyResolutionListeners = propertyResolutionListeners;
         this.embeddedServer = embeddedServer;
         this.applicationContext = applicationContext;
         this.loader = loader;
+        this.taskScheduler = taskScheduler;
     }
 
     /**
@@ -235,8 +240,8 @@ public List<TestContainer> listContainersByScope(@Nullable String scope) {
      * Requests a test resources service shutdown.
      */
     @Post("/stop")
-    public void stopService() {
-        var makeSureServerIsStopped = new Thread(() -> {
+    public boolean stopService() {
+        taskScheduler.schedule(Duration.ofMillis(200), () -> {
             try {
                 try {
                     embeddedServer.stop();
@@ -252,8 +257,7 @@ public void stopService() {
                 System.exit(0);
             }
         });
-        makeSureServerIsStopped.setDaemon(true);
-        makeSureServerIsStopped.start();
+        return true;
     }
 
     private void closeResolvers() {