Add a non-daemon thread. (#9642)

Signed-off-by: Cody Littley <cody@swirldslabs.com>

platform-sdk/swirlds-platform-core/src/main/java/com/swirlds/platform/JvmAnchor.java

@@ -0,0 +1,77 @@
+/*
+ * Copyright (C) 2023 Hedera Hashgraph, LLC
+ *
+ * Licensed 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 com.swirlds.platform;
+
+import static java.util.concurrent.TimeUnit.SECONDS;
+
+import com.swirlds.base.state.Startable;
+import com.swirlds.base.state.Stoppable;
+import com.swirlds.common.threading.framework.config.ThreadConfiguration;
+import com.swirlds.common.threading.manager.ThreadManager;
+import edu.umd.cs.findbugs.annotations.NonNull;
+
+/**
+ * Creates a non-daemon JVM thread that does nothing. Keeps the JVM alive if all other threads are daemon threads.
+ */
+public class JvmAnchor implements Startable, Stoppable {
+
+    private final Thread thread;
+
+    /**
+     * Constructor.
+     *
+     * @param threadManager the thread manager
+     */
+    public JvmAnchor(@NonNull final ThreadManager threadManager) {
+        thread = new ThreadConfiguration(threadManager)
+                .setComponent("platform")
+                .setThreadName("jvm-anchor")
+                .setRunnable(this::run)
+                .setDaemon(false)
+                .build();
+    }
+
+    /**
+     * {@inheritDoc}
+     */
+    @Override
+    public void start() {
+        thread.start();
+    }
+
+    /**
+     * {@inheritDoc}
+     */
+    @Override
+    public void stop() {
+        thread.interrupt();
+    }
+
+    /**
+     * Runs and does nothing until interrupted.
+     */
+    private void run() {
+        while (!Thread.currentThread().isInterrupted()) {
+            try {
+                SECONDS.sleep(Integer.MAX_VALUE);
+            } catch (final InterruptedException e) {
+                Thread.currentThread().interrupt();
+                return;
+            }
+        }
+    }
+}

platform-sdk/swirlds-platform-core/src/main/java/com/swirlds/platform/SwirldsPlatform.java

@@ -737,6 +737,10 @@ public class SwirldsPlatform implements Platform {
                         Pair.of(consensusRoundHandler, "consensusRoundHandler"),
                         Pair.of(transactionPool, "transactionPool")));
 
+        if (platformContext.getConfiguration().getConfigData(ThreadConfig.class).jvmAnchor()) {
+            components.add(new JvmAnchor(threadManager));
+        }
+
         // To be removed once the GUI component is better integrated with the platform.
         GuiPlatformAccessor.getInstance().setShadowGraph(selfId, shadowGraph);
         GuiPlatformAccessor.getInstance().setStateManagementComponent(selfId, stateManagementComponent);

platform-sdk/swirlds-platform-core/src/main/java/com/swirlds/platform/config/ThreadConfig.java

@@ -24,22 +24,20 @@
 /**
  * Thread related config
  *
- * @param logStackTracePauseDuration
- * 		If a thread takes longer than this duration to {@link StoppableThread#pause()}, log a stack trace for debugging
- * 		purposes. A value of {@link Duration#ZERO} means never log.
- * @param threadPrioritySync
- * 		priority for threads that sync (in SyncCaller, SyncListener, SyncServer)
- * @param threadPriorityNonSync
- * 		priority for threads that don't sync (all but SyncCaller, SyncListener,SyncServer)
- * @param threadDumpPeriodMs
- * 		period of generating thread dump file in the unit of milliseconds
- * @param threadDumpLogDir
- * 		thread dump files will be generated in this directory
+ * @param logStackTracePauseDuration If a thread takes longer than this duration to {@link StoppableThread#pause()}, log
+ *                                   a stack trace for debugging purposes. A value of {@link Duration#ZERO} means never
+ *                                   log.
+ * @param threadPrioritySync         priority for threads that sync (in SyncCaller, SyncListener, SyncServer)
+ * @param threadPriorityNonSync      priority for threads that don't sync (all but SyncCaller, SyncListener,SyncServer)
+ * @param threadDumpPeriodMs         period of generating thread dump file in the unit of milliseconds
+ * @param threadDumpLogDir           thread dump files will be generated in this directory
+ * @param jvmAnchor                  if true then create a non-daemon thread that will keep the JVM alive
  */
 @ConfigData("thread")
 public record ThreadConfig(
         @ConfigProperty(defaultValue = "5s") Duration logStackTracePauseDuration,
         @ConfigProperty(defaultValue = "5") int threadPrioritySync,
         @ConfigProperty(defaultValue = "5") int threadPriorityNonSync,
         @ConfigProperty(defaultValue = "0") long threadDumpPeriodMs,
-        @ConfigProperty(defaultValue = "data/threadDump") String threadDumpLogDir) {}
+        @ConfigProperty(defaultValue = "data/threadDump") String threadDumpLogDir,
+        @ConfigProperty(defaultValue = "true") boolean jvmAnchor) {}