1 files changed, 152 insertions, 0 deletions
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/util/ShutdownHook.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/util/ShutdownHook.java
new file mode 100644
index 0000000000..f6b4723489
--- /dev/null
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/internal/util/ShutdownHook.java
@@ -0,0 +1,152 @@
+/*
+ * 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.TimeUnit;
+import java.util.concurrent.TimeoutException;
+import java.util.concurrent.atomic.AtomicBoolean;
+
+import org.eclipse.jgit.internal.JGitText;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * The singleton {@link ShutdownHook} provides a means to register
+ * {@link Listener}s that are run when JGit is uninstalled, either
+ * <ul>
+ * <li>in an OSGi framework when this bundle is deactivated, or</li>
+ * <li>otherwise, when the JVM as a whole shuts down.</li>
+ * </ul>
+ */
+@SuppressWarnings("ImmutableEnumChecker")
+public enum ShutdownHook {
+	/**
+	 * Singleton
+	 */
+	INSTANCE;
+
+	/**
+	 * Object that needs to cleanup on shutdown.
+	 */
+	public interface Listener {
+		/**
+		 * Cleanup resources when JGit is shut down.
+		 * <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 final AtomicBoolean shutdownInProgress = new AtomicBoolean();
+
+	private ShutdownHook() {
+		CleanupService.getInstance().register(this::cleanup);
+	}
+
+	private void cleanup() {
+		if (!shutdownInProgress.getAndSet(true)) {
+			ExecutorService runner = Executors.newWorkStealingPool();
+			try {
+				runner.submit(() -> {
+					this.doCleanup();
+					return null;
+				}).get(30L, TimeUnit.SECONDS);
+			} catch (InterruptedException | ExecutionException
+					| TimeoutException e) {
+				throw new RuntimeException(e.getMessage(), e);
+			} finally {
+				runner.shutdownNow();
+			}
+		}
+	}
+
+	private void doCleanup() {
+		listeners.parallelStream().forEach(this::notify);
+	}
+
+	private void notify(Listener l) {
+		LOG.debug(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 JGit shutdown if it is not
+	 * already registered. Registration is disabled when JGit shutdown is
+	 * already in progress.
+	 *
+	 * @param l
+	 *            the object to call {@link Listener#onShutdown} on when JGit
+	 *            shuts down
+	 * @return {@code true} if this object has been registered
+	 */
+	public boolean register(Listener l) {
+		if (shutdownInProgress.get()) {
+			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 JGit shutdown if it
+	 * is still registered. Unregistration is disabled when JGit 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.get()) {
+			return !listeners.contains(l);
+		}
+		LOG.debug("unregister {} from shutdown hook", l); //$NON-NLS-1$
+		listeners.remove(l);
+		return true;
+	}
+
+	/**
+	 * Whether a JGit shutdown is in progress
+	 *
+	 * @return {@code true} if a JGit shutdown is in progress
+	 */
+	public boolean isShutdownInProgress() {
+		return shutdownInProgress.get();
+	}
+}