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/*
 * Copyright (C) 2020 Graylog, Inc.
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the Server Side Public License, version 1,
 * as published by MongoDB, Inc.
 *
 * 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
 * Server Side Public License for more details.
 *
 * You should have received a copy of the Server Side Public License
 * along with this program. If not, see
 * .
 */
/*
 *
 * Taken from
 * https://github.com/Netflix/netflix-commons/blob/v0.3.0/netflix-commons-util/src/main/java/com/netflix/util/concurrent/ConcurrentUUIDFactory.java
 *
 * Original License:
 *
 * Copyright 2015 Netflix, Inc.
 *
 * 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 org.graylog.util.uuid;

import java.util.Random;
import java.util.UUID;
import java.util.concurrent.ThreadLocalRandom;

public class ConcurrentUUID {
    /**
     * Generate a random UUID v4 that will perform reasonably when used by
     * multiple threads under load.
     *
     * @see ConcurrentUUIDFactory
     * @return random UUID
     */
    public static UUID generateRandomUuid() {
        final Random rnd = ThreadLocalRandom.current();
        long mostSig  = rnd.nextLong();
        long leastSig = rnd.nextLong();

        // Identify this as a version 4 UUID, that is one based on a random value.
        mostSig &= 0xffffffffffff0fffL;
        mostSig |= 0x0000000000004000L;

        // Set the variant identifier as specified for version 4 UUID values.  The two
        // high order bits of the lower word are required to be one and zero, respectively.
        leastSig &= 0x3fffffffffffffffL;
        leastSig |= 0x8000000000000000L;

        return new UUID(mostSig, leastSig);
    }
}