#5737 - Nima: Add WebServer.Builder configuration option to support not registering JVM shutdown hook

- Add WebServer.Builder.shutdownHook(false) configuration option
- Add support for de-registering the shutdown hook when the webserver is explicitly stopped
- Modify HelidonServerJunitExtension to use shutdownHook(false)

Author: rbygrave

lra/coordinator/server/src/test/java/io/helidon/lra/coordinator/CoordinatorTest.java

@@ -63,6 +63,7 @@ static void beforeAll() {
                         .build().get(CoordinatorService.CONFIG_PREFIX))
                 .build();
         server = WebServer.builder()
+                .shutdownHook(true)
                 .host("localhost")
                 .routing(r -> r.register(CONTEXT_PATH, () -> rules -> rules.put((req, res) -> res.send())))
                 .socket(COORDINATOR_ROUTING_NAME, (socket, routing) -> {

nima/testing/junit5/webserver/src/main/java/io/helidon/nima/testing/junit5/webserver/HelidonServerJunitExtension.java

@@ -76,6 +76,7 @@ public void beforeAll(ExtensionContext context) {
 
         WebServer.Builder builder = WebServer.builder()
                 .port(0)
+                .shutdownHook(false)
                 .host("localhost");
 
         setupServer(builder);

nima/webserver/webserver/src/main/java/io/helidon/nima/webserver/LoomServer.java

@@ -44,11 +44,14 @@ class LoomServer implements WebServer {
     private final AtomicBoolean running = new AtomicBoolean();
     private final Lock lifecycleLock = new ReentrantLock();
     private final ExecutorService executorService;
+    private final boolean registerShutdownHook;
+    private volatile Thread shutdownHook;
 
     private volatile List<ListenerFuture> startFutures;
     private volatile boolean alreadyStarted = false;
 
     LoomServer(Builder builder, DirectHandlers simpleHandlers) {
+        this.registerShutdownHook = builder.shutdownHook();
         ServerContextImpl serverContext = new ServerContextImpl(builder.context(),
                                                                 builder.mediaContext(),
                                                                 builder.contentEncodingContext());
@@ -162,6 +165,7 @@ private void stopIt() {
         running.set(false);
 
         LOGGER.log(System.Logger.Level.INFO, "Níma server stopped all channels.");
+        deregisterShutdownHook();
     }
 
     private void startIt() {
@@ -175,13 +179,9 @@ private void startIt() {
             }
             return;
         }
-        Runtime.getRuntime()
-                .addShutdownHook(new Thread(() -> {
-                    listeners.values().forEach(ServerListener::stop);
-                    if (startFutures != null) {
-                        startFutures.forEach(future -> future.future().cancel(true));
-                    }
-                }, "shutdown-hook"));
+        if (registerShutdownHook) {
+            registerShutdownHook();
+        }
         now = System.currentTimeMillis() - now;
         long uptime = ManagementFactory.getRuntimeMXBean().getUptime();
 
@@ -197,6 +197,24 @@ private void startIt() {
         }
     }
 
+    private void registerShutdownHook() {
+        this.shutdownHook = new Thread(() -> {
+                    listeners.values().forEach(ServerListener::stop);
+                    if (startFutures != null) {
+                        startFutures.forEach(future -> future.future().cancel(true));
+                    }
+                }, "shutdown-hook");
+
+        Runtime.getRuntime().addShutdownHook(shutdownHook);
+    }
+
+    private void deregisterShutdownHook() {
+        if (shutdownHook != null) {
+            Runtime.getRuntime().removeShutdownHook(shutdownHook);
+            shutdownHook = null;
+        }
+    }
+
     // return false if anything fails
     private boolean parallel(String taskName, Consumer<ServerListener> task) {
         boolean result = true;

nima/webserver/webserver/src/main/java/io/helidon/nima/webserver/WebServer.java

@@ -143,6 +143,7 @@ class Builder implements io.helidon.common.Builder<Builder, WebServer>, Router.R
         private MediaContext mediaContext = MediaContext.create();
         private ContentEncodingContext contentEncodingContext = ContentEncodingContext.create();
 
+        private boolean shutdownHook = true;
         private Context context;
 
         Builder(Config rootConfig) {
@@ -407,10 +408,27 @@ public Builder context(Context context) {
             return this;
         }
 
+        /**
+         * When true the webserver registers a shutdown hook with the JVM Runtime.
+         * <p>
+         * Defaults to true. Set this to false such that a shutdown hook is not registered.
+         *
+         * @param shutdownHook When true register a shutdown hook
+         * @return updated builder
+         */
+        public Builder shutdownHook(boolean shutdownHook) {
+            this.shutdownHook = shutdownHook;
+            return this;
+        }
+
         Context context() {
             return context;
         }
 
+        boolean shutdownHook() {
+            return shutdownHook;
+        }
+
         MediaContext mediaContext() {
             return this.mediaContext;
         }