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/*******************************************************************************
 * Copyright (c) 2022, 2024 IBM Corporation and others.
 *
 * This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License 2.0
 * which accompanies this distribution, and is available at
 * https://www.eclipse.org/legal/epl-2.0/
 *
 * SPDX-License-Identifier: EPL-2.0
 *
 * Contributors:
 *     IBM Corporation - initial API and implementation
 *******************************************************************************/
package org.eclipse.osgi.internal.container;

import java.lang.ref.ReferenceQueue;
import java.lang.ref.WeakReference;
import java.util.concurrent.ConcurrentHashMap;
import java.util.function.Function;

public final class KeyBasedLockStore {

	final ReferenceQueue refQueue = new ReferenceQueue<>();
	private final ConcurrentHashMap lockMap = new ConcurrentHashMap<>();
	private final Function lockCreator;

	public KeyBasedLockStore(Function lockCreator) {
		this.lockCreator = lockCreator;
	}

	private final class LockWeakRef extends WeakReference {
		final Key key;

		public LockWeakRef(Lock referent, Key keyValue) {
			super(referent, refQueue);
			key = keyValue;
		}
	}

	public final Lock getLock(Key key) {
		poll();
		LockWeakRef lockRef = lockMap.get(key);
		Lock lock = lockRef != null ? lockRef.get() : null;
		if (lock != null) {
			return lock;
		}

		lock = lockCreator.apply(key);

		while (true) {
			LockWeakRef retVal = lockMap.putIfAbsent(key, new LockWeakRef(lock, key));
			if (retVal == null) {
				return lock;
			}

			Lock retLock = retVal.get();
			if (retLock != null) {
				return retLock;
			}
			lockMap.remove(key, retVal);
		}
	}

	@SuppressWarnings("unchecked")
	private final void poll() {
		LockWeakRef lockRef;
		while ((lockRef = (LockWeakRef) refQueue.poll()) != null) {
			lockMap.remove(lockRef.key, lockRef);
		}
	}
}