--- /dev/null
+/*
+ * Copyright (C) 2023, SAP SE and others
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Distribution License v. 1.0 which is available at
+ * https://www.eclipse.org/org/documents/edl-v10.php.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+package org.eclipse.jgit.internal.util;
+
+import java.text.MessageFormat;
+import java.util.Set;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.ExecutionException;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.RejectedExecutionException;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.TimeoutException;
+
+import org.eclipse.jgit.internal.JGitText;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * A hook registered as a JVM shutdown hook managing a set of objects needing
+ * cleanup during JVM shutdown. See {@link Runtime#addShutdownHook}.
+ */
+public enum ShutdownHook {
+ /**
+ * Singleton
+ */
+ INSTANCE;
+
+ /**
+ * Object that needs to cleanup on JVM shutdown.
+ */
+ public interface Listener {
+ /**
+ * Cleanup resources when JVM shuts down, called from JVM shutdown hook.
+ * <p>
+ * Implementations should be coded defensively
+ * <ul>
+ * <li>they should finish their work quickly
+ * <li>they should be written to be thread-safe and to avoid deadlocks
+ * insofar as possible
+ * <li>they should not rely blindly upon services that may have
+ * registered their own shutdown hooks and therefore may themselves be
+ * in the process of shutting down
+ * <li>attempts to use other thread-based services may lead to
+ * deadlocks.
+ * </ul>
+ * See {@link Runtime#addShutdownHook} for more details.
+ */
+ public void onShutdown();
+ }
+
+ private static final Logger LOG = LoggerFactory
+ .getLogger(ShutdownHook.class);
+
+ private final Set<Listener> listeners = ConcurrentHashMap.newKeySet();
+
+ private volatile boolean shutdownInProgress;
+
+ private ShutdownHook() {
+ try {
+ Runtime.getRuntime().addShutdownHook(new Thread(this::cleanup));
+ } catch (IllegalStateException e) {
+ // ignore - the VM is already shutting down
+ }
+ }
+
+ private void cleanup() {
+ shutdownInProgress = true;
+ ExecutorService runner = Executors.newWorkStealingPool();
+ try {
+ runner.submit(() -> {
+ this.doCleanup();
+ return null;
+ }).get(30L, TimeUnit.SECONDS);
+ } catch (RejectedExecutionException | InterruptedException
+ | ExecutionException | TimeoutException e) {
+ LOG.error(JGitText.get().shutdownCleanupFailed, e);
+ }
+ runner.shutdownNow();
+ }
+
+ private void doCleanup() {
+ listeners.parallelStream().forEach(this::notify);
+ }
+
+ private void notify(Listener l) {
+ LOG.warn(JGitText.get().shutdownCleanup, l);
+ try {
+ l.onShutdown();
+ } catch (RuntimeException e) {
+ LOG.error(MessageFormat.format(
+ JGitText.get().shutdownCleanupListenerFailed, l), e);
+ }
+ }
+
+ /**
+ * Register object that needs cleanup during JVM shutdown if it is not
+ * already registered. Registration is disabled when JVM shutdown is already
+ * in progress.
+ *
+ * @param l
+ * the object to call {@link Listener#onShutdown} on when JVM
+ * shuts down
+ * @return {@code true} if this object has been registered
+ */
+ public boolean register(Listener l) {
+ if (shutdownInProgress) {
+ return listeners.contains(l);
+ }
+ LOG.debug("register {} with shutdown hook", l); //$NON-NLS-1$
+ listeners.add(l);
+ return true;
+ }
+
+ /**
+ * Unregister object that no longer needs cleanup during JVM shutdown if it
+ * is still registered. Unregistration is disabled when JVM shutdown is
+ * already in progress.
+ *
+ * @param l
+ * the object registered to be notified for cleanup when the JVM
+ * shuts down
+ * @return {@code true} if this object is no longer registered
+ */
+ public boolean unregister(Listener l) {
+ if (shutdownInProgress) {
+ return !listeners.contains(l);
+ }
+ LOG.debug("unregister {} from shutdown hook", l); //$NON-NLS-1$
+ listeners.remove(l);
+ return true;
+ }
+
+ /**
+ * Whether a JVM shutdown is in progress
+ *
+ * @return {@code true} if a JVM shutdown is in progress
+ */
+ public boolean isShutdownInProgress() {
+ return shutdownInProgress;
+ }
+}
projects / jgit.git / commitdiff