C# helper class that generates numbers and IDs sequentially, in a thread-safe manner.

using System;
using System.Threading;

/// <summary>
/// Generates numbers and ids sequentially in a thread-safe manner
/// </summary>
public class SequenceGenerator
{
    bool _excludeNegativeNumbers;
    long _current;

    /// <summary>
    /// Initializes a new <see cref="SequenceGenerator"/>
    /// </summary>
    /// <param name="startValue">Value to start generating sequences from</param>
    /// <param name="excludeNegativeNumbers">Set to true to always generate positive numbers, false to include the negative number range</param>
    public SequenceGenerator(long startValue, bool excludeNegativeNumbers)
    {
        if (!excludeNegativeNumbers && startValue < 0) throw new ArgumentException("startValue argument is negative while excludeNegativeNumbers argument is set to true!");
        this._excludeNegativeNumbers = excludeNegativeNumbers;
        _current = startValue - 1;
    }

    public static SequenceGenerator FromUtcNow()
    {
        return new SequenceGenerator(DateTime.UtcNow.Ticks, false);
    }

    public long GetNext()
    {
        var val = Interlocked.Increment(ref _current);

        if(val < 0 && _excludeNegativeNumbers)
        {
            do
            {
                if (Interlocked.CompareExchange(ref _current, 0, val) == val)
                {
                    //Current was successfully set to 0;
                    val = 0;
                    break;
                }
                else
                {
                    //A different thread changed _current, so increment and read again
                    val = Interlocked.Increment(ref _current);
                }
            }
            while (val < 0);
        }

        return val;
    }

    public string GetNextId()
    {
        return GetNext().ToString("x");
    }
}

//
// Usage
//

var correlationIdGen = SequenceGenerator.FromUtcNow();
System.Console.WriteLine(correlationIdGen.GetNextId());
System.Console.WriteLine(correlationIdGen.GetNextId());

//
// Also see <https://github.com/tenor/RestBus/blob/283671e21e53bf3ae275469295baa81d7b388797/src/Brokers/RabbitMQ/RestBus.RabbitMQ/Client/RestBusClient.cs>
// real-world example (line: 16 - `static SequenceGenerator correlationIdGen = SequenceGenerator.FromUtcNow();`)