Personally, the database option sounds like overkill to me just based on the notion of storing current users. If you are actually storing more than that, then using a database may make sense. But assuming you simply want a list of current users from both instances of your WCF service, I would use an in-memory solution, something like a static generic dictionary. As long as the services can be uniquely identified, I'd use the unique service ID as the key into the dictionary and just pair each key with a generic list of user names (or some appropriate user data structure) for that service. Something like:
private static Dictionary<Guid, List<string>> _currentUsers;
Since this dictionary would be shared between two WCF services, you'll need to synchronize access to it. Here's an example.
public class MyWCFService : IMyWCFService
{
private static Dictionary<Guid, List<string>> _currentUsers =
new Dictionary<Guid, List<string>>();
private void AddUser(Guid serviceID, string userName)
{
// Synchronize access to the collection via the SyncRoot property.
lock (((ICollection)_currentUsers).SyncRoot)
{
// Check if the service's ID has already been added.
if (!_currentUsers.ContainsKey(serviceID))
{
_currentUsers[serviceID] = new List<string>();
}
// Make sure to only store the user name once for each service.
if (!_currentUsers[serviceID].Contains(userName))
{
_currentUsers[serviceID].Add(userName);
}
}
}
private void RemoveUser(Guid serviceID, string userName)
{
// Synchronize access to the collection via the SyncRoot property.
lock (((ICollection)_currentUsers).SyncRoot)
{
// Check if the service's ID has already been added.
if (_currentUsers.ContainsKey(serviceID))
{
// See if the user name exists.
if (_currentUsers[serviceID].Contains(userName))
{
_currentUsers[serviceID].Remove(userName);
}
}
}
}
}
Given that you don't want users listed twice for a specific service, it would probably make sense to replace the List<string> with HashSet<string>.