64 bits Sufficiently Unique Id Generator

SUID.cs

/****************************************************************************
 * Copyright 2009-2020 Jean-Philippe Gravel, P. Eng. PSEM
 * Conversion to C# from https://gist.github.com/formix/d9521fd49cbeee305e2a
 * 
 * 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.
 ***************************************************************************/
using System;
using System.Security.Cryptography;

namespace Utils
{
    /// <summary>
    /// Sufficiently unique identifier.
    /// </summary>
    public static class SUID
    {
        private static ushort _counter = 0;
        private static readonly object _mutex = new object();

        static SUID()
        {
            var word = new byte[2];
            RandomNumberGenerator.Create().GetBytes(word);
            _counter = BitConverter.ToUInt16(word, 0);
        }

        /// <summary>
        /// Creates a unique 64 bits ID by aggregating the current time in
        /// milliseconds since epoch(Jan. 1, 1) and using a 16 bits counter.The
        /// counter is initialized at a random number.This generator can create up
        /// to 65536 different id per millisecond, which translate to 1 id every
        /// 16 microseconds.
        /// </summary>
        /// <returns>A new 64 bit value.</returns>
        public static ulong Next()
        {
            lock (_mutex)
            {
                ulong now = (ulong)(DateTime.Now.Ticks / 10000);
                ulong id = (now << 16) | _counter;
                _counter++;
                return id;
            }
        }
    }
}