Correlation Part 1: The Context

CorrelationContext.cs

public static class CorrelationContext
{
    public static Stack<Guid> GetCorrelationStack() {}
    public static Guid? GetCorrelationId() {}
    public static IDisposable CreateCorrelation(Guid? correlationId = null) {}
    public static IDisposable CreateCorrelationIfNotExists(Guid? correlationId = null) {}
}

CorrelationContext_Example.cs

class Program
{
    static void Main(string[] args)
    {
        using(CorrelationContext.CreateCorrelationIfNotExists())
        {
            Console.WriteLine(CorrelationContext.GetCorrelationId());

            using(CorrelationContext.CreateCorrelationIfNotExists())
            {
                Console.WriteLine(CorrelationContext.GetCorrelationId());
            }
        }
    }
}

CorrelationContext_Full.cs

public static class CorrelationContext
{
    private static readonly AsyncLocal<Stack<Guid>> _correlationStack = new AsyncLocal<Stack<Guid>>();
    public static Stack<Guid> GetCorrelationStack() => _correlationStack.Value ?? new Stack<Guid>();
    public static Guid? GetCorrelationId() 
    {
        var stack = GetCorrelationStack();
        if(stack.Count > 0)
            return stack.Peek();

        return null; // TODO :: decide what you are going to do
    } 
    public static IDisposable CreateCorrelation(Guid? correlationId = null)
    {
        lock(_correlationStack)
        {
            if (_correlationStack.Value == null)
                _correlationStack.Value = new Stack<Guid>();

            _correlationStack.Value.Push(correlationId ?? Guid.NewGuid());
        }

        return new DisposeCorrelation(_correlationStack);
    }
    public static IDisposable CreateCorrelationIfNotExists(Guid? correlationId = null)
    {
        if(GetCorrelationStack().Count > 0)
            return new EmptyDisposable();

        return CreateCorrelation(correlationId);
    }
    private class EmptyDisposable : IDisposable { public void Dispose() { } }
    private class DisposeCorrelation : IDisposable
    {
        private readonly AsyncLocal<Stack<Guid>> _localStack;

        public DisposeCorrelation(AsyncLocal<Stack<Guid>> localStack)
        {
            _localStack = localStack;
        }
        public void Dispose()
        {
            var stack = _localStack.Value ?? new Stack<Guid>();

            if(stack.Count > 0)
                stack.Pop();
        }
    }
}

Create_Correlation.cs

public static IDisposable CreateCorrelation(Guid? correlationId = null)
{
    lock(_correlationStack)
    {
        if (_correlationStack.Value == null)
            _correlationStack.Value = new Stack<Guid>();

        _correlationStack.Value.Push(correlationId ?? Guid.NewGuid());
    }

    return new DisposeCorrelation(_correlationStack);
}

Create_Correlation_If_Not_Exists.cs

public static IDisposable CreateCorrelationIfNotExists(Guid? correlationId = null)
{
    if(GetCorrelationStack().Count > 0)
        return new EmptyDisposable();

    return CreateCorrelation(correlationId);
}

Dispose_Correlation.cs

private class DisposeCorrelation : IDisposable
{
    private readonly AsyncLocal<Stack<Guid>> _localStack;

    public DisposeCorrelation(AsyncLocal<Stack<Guid>> localStack)
    {
        _localStack = localStack;
    }
    public void Dispose()
    {
        var stack = _localStack.Value ?? new Stack<Guid>();

        if(stack.Count > 0)
            stack.Pop();
    }
}

Get_Correlation_Id.cs

public static Guid? GetCorrelationId() 
{
    var stack = GetCorrelationStack();
    if(stack.Count > 0)
        return stack.Peek();

    return null; // TODO :: decide what you are going to do
} 

Get_Correlation_Stack.cs

private static readonly AsyncLocal<Stack<Guid>> _correlationStack = new AsyncLocal<Stack<Guid>>();
public static Stack<Guid> GetCorrelationStack() => _correlationStack.Value ?? new Stack<Guid>();