Instance Re-entrancy Guard

gistfile1.txt

using System;
using System.Runtime.CompilerServices;

internal class InstanceReEntrancyGuard : IDisposable {
	private class Ref<T> where T : struct { public T Value { get; set; } }
	private static readonly ConditionalWeakTable<Object, Ref<Boolean>> reEntranceEphemerons = new ConditionalWeakTable<Object, Ref<Boolean>>();
	private readonly Ref<Boolean> hasEnteredOnce;
	public InstanceReEntrancyGuard(Object instance, String reEntrantMessage = null) {
		hasEnteredOnce = reEntranceEphemerons.GetValue(instance, x => new Ref<Boolean>());
		if (hasEnteredOnce.Value)
			throw new InvalidOperationException((hasEnteredOnce.Value ? "Re-entrance detected." : null) + (String.IsNullOrWhiteSpace(reEntrantMessage) ? null : (" " + reEntrantMessage)));
		hasEnteredOnce.Value = true;
	}
	public void Dispose() {
		hasEnteredOnce.Value = false;
	}
}