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Neo4j kernel is a lightweight, embedded Java database designed to store data structured as graphs rather than tables. For more information, see http://neo4j.org.

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/*
 * Copyright (c) "Neo4j"
 * Neo4j Sweden AB [https://neo4j.com]
 *
 * This file is part of Neo4j.
 *
 * Neo4j is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see .
 */
package org.neo4j.kernel.database;

import org.neo4j.kernel.api.KernelTransaction;
import org.neo4j.kernel.impl.api.KernelTransactionImplementation;
import org.neo4j.kernel.impl.locking.LockManager;
import org.neo4j.lock.Lock;
import org.neo4j.lock.LockTracer;
import org.neo4j.lock.ResourceType;

interface UpgradeLocker {
    Lock acquireWriteLock(KernelTransaction tx);

    Lock acquireReadLock(KernelTransaction tx);

    UpgradeLocker DEFAULT = new UpgradeLocker() {
        private static final long ID = Long.MAX_VALUE;
        private final ResourceType type = ResourceType.NODE;

        @Override
        public Lock acquireWriteLock(KernelTransaction tx) {
            LockManager.Client lockClient = getLockClient(tx);
            lockClient.acquireExclusive(LockTracer.NONE, type, ID);
            return new Lock() {
                @Override
                public void release() {
                    lockClient.releaseExclusive(type, ID);
                }
            };
        }

        @Override
        public Lock acquireReadLock(KernelTransaction tx) {
            LockManager.Client lockClient = getLockClient(tx);
            lockClient.acquireShared(LockTracer.NONE, type, ID);
            return new Lock() {
                @Override
                public void release() {
                    lockClient.releaseShared(type, ID);
                }
            };
        }

        private LockManager.Client getLockClient(KernelTransaction tx) {
            return ((KernelTransactionImplementation) tx)
                    .lockClient(); // Only one KernelTransaction implementation exists
        }
    };
}