[java] Stopping sessions when the Node is gracefully shutdown

A manager for shutdown hooks was added, so the http client
is closed after all shutdown hooks that potentially need it
are executed.

This will help to stop running Docker containers when the Node
or Standalone are gracefully shutdown and sessions are still
running.

Author: diemol

java/src/org/openqa/selenium/grid/node/httpd/NodeServer.java

@@ -17,6 +17,14 @@
 
 package org.openqa.selenium.grid.node.httpd;
 
+import static java.net.HttpURLConnection.HTTP_INTERNAL_ERROR;
+import static java.net.HttpURLConnection.HTTP_NO_CONTENT;
+import static org.openqa.selenium.grid.config.StandardGridRoles.EVENT_BUS_ROLE;
+import static org.openqa.selenium.grid.config.StandardGridRoles.HTTPD_ROLE;
+import static org.openqa.selenium.grid.config.StandardGridRoles.NODE_ROLE;
+import static org.openqa.selenium.grid.data.Availability.DOWN;
+import static org.openqa.selenium.remote.http.Route.get;
+
 import com.google.auto.service.AutoService;
 import com.google.common.collect.ImmutableSet;
 import com.google.common.net.MediaType;
@@ -46,6 +54,7 @@
 import org.openqa.selenium.grid.server.NetworkOptions;
 import org.openqa.selenium.grid.server.Server;
 import org.openqa.selenium.internal.Require;
+import org.openqa.selenium.internal.ShutdownHooks;
 import org.openqa.selenium.netty.server.NettyServer;
 import org.openqa.selenium.remote.http.Contents;
 import org.openqa.selenium.remote.http.HttpClient;
@@ -60,14 +69,6 @@
 import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.logging.Logger;
 
-import static java.net.HttpURLConnection.HTTP_INTERNAL_ERROR;
-import static java.net.HttpURLConnection.HTTP_NO_CONTENT;
-import static org.openqa.selenium.grid.config.StandardGridRoles.EVENT_BUS_ROLE;
-import static org.openqa.selenium.grid.config.StandardGridRoles.HTTPD_ROLE;
-import static org.openqa.selenium.grid.config.StandardGridRoles.NODE_ROLE;
-import static org.openqa.selenium.grid.data.Availability.DOWN;
-import static org.openqa.selenium.remote.http.Route.get;
-
 @AutoService(CliCommand.class)
 public class NodeServer extends TemplateGridServerCommand {
 
@@ -226,7 +227,7 @@ public NettyServer start() {
   protected void execute(Config config) {
     Require.nonNull("Config", config);
 
-    Runtime.getRuntime().addShutdownHook(shutdownHook);
+    ShutdownHooks.add(shutdownHook);
     Server<?> server = asServer(config).start();
 
     BuildInfo info = new BuildInfo();

java/src/org/openqa/selenium/grid/node/local/LocalNode.java

@@ -66,8 +66,10 @@
 import org.openqa.selenium.grid.node.SessionFactory;
 import org.openqa.selenium.grid.node.config.NodeOptions;
 import org.openqa.selenium.grid.security.Secret;
+import org.openqa.selenium.internal.Debug;
 import org.openqa.selenium.internal.Either;
 import org.openqa.selenium.internal.Require;
+import org.openqa.selenium.internal.ShutdownHooks;
 import org.openqa.selenium.io.TemporaryFilesystem;
 import org.openqa.selenium.io.Zip;
 import org.openqa.selenium.json.Json;
@@ -141,16 +143,17 @@ private LocalNode(
     Require.nonNull("Registration secret", registrationSecret);
 
     this.healthCheck = healthCheck == null ?
-      () -> new HealthCheck.Result(
-        isDraining() ? DRAINING : UP,
-        String.format("%s is %s", uri, isDraining() ? "draining" : "up")) :
-      healthCheck;
+                       () -> new HealthCheck.Result(
+                         isDraining() ? DRAINING : UP,
+                         String.format("%s is %s", uri, isDraining() ? "draining" : "up")) :
+                       healthCheck;
 
     this.currentSessions = CacheBuilder.newBuilder()
       .expireAfterAccess(sessionTimeout)
       .ticker(ticker)
       .removalListener((RemovalListener<SessionId, SessionSlot>) notification -> {
         // Attempt to stop the session
+        LOG.log(Debug.getDebugLogLevel(), "Stopping session %s", notification.getKey().toString());
         SessionSlot slot = notification.getValue();
         if (!slot.isAvailable()) {
           slot.stop();
@@ -185,6 +188,7 @@ private LocalNode(
       }
     }));
 
+    ShutdownHooks.add(new Thread(this::stopAllSessions));
     new JMXHelper().register(this);
   }
 
@@ -438,6 +442,13 @@ public void stop(SessionId id) throws NoSuchSessionException {
     tempFileSystems.invalidate(id);
   }
 
+  private void stopAllSessions() {
+    if (currentSessions.size() > 0) {
+      LOG.info("Trying to stop all running sessions before shutting down...");
+      currentSessions.invalidateAll();
+    }
+  }
+
   private Session createExternalSession(ActiveSession other, URI externalUri,
                                         boolean isSupportingCdp) {
     Capabilities toUse = ImmutableCapabilities.copyOf(other.getCapabilities());

java/src/org/openqa/selenium/internal/ShutdownHooks.java

@@ -0,0 +1,88 @@
+// Licensed to the Software Freedom Conservancy (SFC) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The SFC licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+package org.openqa.selenium.internal;
+
+import java.util.Collection;
+import java.util.IdentityHashMap;
+
+/**
+ * A simple manager for shutdown hooks, with plenty of room for improvement.
+ */
+public class ShutdownHooks {
+
+  private static IdentityHashMap<Thread, Thread> defaultHooks;
+  private static IdentityHashMap<Thread, Thread> atEndHooks;
+
+  static {
+    defaultHooks = new IdentityHashMap<>();
+    atEndHooks = new IdentityHashMap<>();
+    Runtime.getRuntime().addShutdownHook(new Thread(ShutdownHooks::runShutdownHooks));
+  }
+
+  private ShutdownHooks() {
+    // Utility class
+  }
+
+  public static void add(Thread hook, HookExecutionStrategy strategy) {
+    if (strategy.equals(HookExecutionStrategy.DEFAULT)) {
+      defaultHooks.put(hook, hook);
+    } else {
+      atEndHooks.put(hook, hook);
+    }
+  }
+
+  public static void add(Thread hook) {
+    add(hook, HookExecutionStrategy.DEFAULT);
+  }
+
+  static void runShutdownHooks() {
+    Collection<Thread> threads;
+    synchronized (ShutdownHooks.class) {
+      threads = defaultHooks.keySet();
+      defaultHooks = null;
+    }
+    runHooks(threads);
+    Collection<Thread> atEndThreads;
+    synchronized (ShutdownHooks.class) {
+      atEndThreads = atEndHooks.keySet();
+      atEndHooks = null;
+    }
+    runHooks(atEndThreads);
+  }
+
+  private static void runHooks(Collection<Thread> threads) {
+    for (Thread hook : threads) {
+      hook.start();
+    }
+    for (Thread hook : threads) {
+      while (true) {
+        try {
+          hook.join();
+          break;
+        } catch (InterruptedException ignored) {
+        }
+      }
+    }
+  }
+
+  public enum HookExecutionStrategy {
+    AT_END,      // Hook will be executed after all DEFAULT ones are executed
+    DEFAULT      // Hook will be executed before all AT_END ones
+  }
+
+}

java/src/org/openqa/selenium/remote/http/netty/NettyClient.java

@@ -17,6 +17,8 @@
 
 package org.openqa.selenium.remote.http.netty;
 
+import static org.openqa.selenium.internal.ShutdownHooks.HookExecutionStrategy.AT_END;
+
 import com.google.auto.service.AutoService;
 
 import org.asynchttpclient.AsyncHttpClient;
@@ -27,6 +29,7 @@
 import org.openqa.selenium.Credentials;
 import org.openqa.selenium.UsernameAndPassword;
 import org.openqa.selenium.internal.Require;
+import org.openqa.selenium.internal.ShutdownHooks;
 import org.openqa.selenium.remote.http.ClientConfig;
 import org.openqa.selenium.remote.http.Filter;
 import org.openqa.selenium.remote.http.HttpClient;
@@ -71,7 +74,7 @@ private NettyClient(ClientConfig config) {
     this.handler = new NettyHttpHandler(config, client).with(config.filter());
     this.toWebSocket = NettyWebSocket.create(config, client);
     if (!addedHook.get()) {
-      Runtime.getRuntime().addShutdownHook(new Thread(this::shutdownClient));
+      ShutdownHooks.add(new Thread(this::shutdownClient), AT_END);
       addedHook.set(true);
     }
   }