Thread-safe access to static collection
private static Dictionary<Type, List<PropertyInfo>> PropertyCache { get; set; }

// I will do this
PropertyCache.Add(typeof(string), new List<PropertyInfo>());
PropertyCache.Remove(typeof(string));

// I will never do this
PropertyCache = new Dictionary<Type, List<PropertyInfo>>();

lock(((ICollection)myObject).SyncRoot)
{
    //Code that should be executed by only one concurrent thread
    //This is add/insert/remove/iterate/clear/etc.
}