public sealed class Singleton {
    private static Singleton instance; // zadny "= null"
    private static readonly object padlock = new object();

    public static Singleton Instance {
        get {
            var result = instance;
            if (null == result) { // pro kontrolu na NULL neni potreba lock
                lock(padlock) {
                    // zkontrolujeme jeste jednou, jestli se pred ziskanim zamku nahodou
                    // uz singleton neinicializoval z jinyho vlakna
                    if(null == (result = instance)) {
                        instance = result = new Singleton();
                    }
                }
            }

            return result;
        }
    }
}