List all active ASP.NET Sessions

Question

How can I list (and iterate through) all current ASP.NET sessions?

Answer 1

Here's a WebForms/Identity example that gets a list of the logged on users active within the last 30 minutes.

The answer below works for a single web server, and the cache will be lost if the application restarts. If you want to persist the data and share it between servers in a web farm, this answer might be of interest.

In Global.asa.cs:

public static ActiveUsersCache ActiveUsersCache { get; } = new ActiveUsersCache();

and

protected void Application_PreRequestHandlerExecute(object sender, EventArgs e)
{
    if (User != null && User.Identity.IsAuthenticated)
    {
        // Only update when the request is for an .aspx page
        if (Context.Handler is System.Web.UI.Page)
        {
            ActiveUsersCache.AddOrUpdate(User.Identity.Name);
        }
    }
}

The add these couple of classes:

public class ActiveUsersCache
{
    private readonly object padlock = new object();
    private readonly Dictionary cache = new Dictionary();
    private DateTime lastCleanedAt;

    public int ActivePeriodInMinutes { get; } = 30;
    private const int MinutesBetweenCacheClean = 30;

    public List GetActiveUsers()
    {
        CleanCache();

        var result = new List();
        lock (padlock)
        {
            result.AddRange(cache.Select(activeUser => new ActiveUser {Name = activeUser.Key, LastActive = activeUser.Value}));
        }
        return result;
    }

    private void CleanCache()
    {
        lastCleanedAt = DateTime.Now;
        var cutoffTime = DateTime.Now - TimeSpan.FromMinutes(ActivePeriodInMinutes);
        lock (padlock)
        {
            var expiredNames = cache.Where(au => au.Value < cutoffTime).Select(au => au.Key).ToList();
            foreach (var name in expiredNames)
            {
                cache.Remove(name);
            }
        }
    }

    public void AddOrUpdate(string userName)
    {
        lock (padlock)
        {
            cache[userName] = DateTime.Now;
        }

        if (IsTimeForCacheCleaup())
        {
            CleanCache();
        }
    }

    private bool IsTimeForCacheCleaup()
    {
        return lastCleanedAt < DateTime.Now - TimeSpan.FromMinutes(MinutesBetweenCacheClean);
    }
}

public class ActiveUser
{
    public string Name { get; set; }

    public DateTime LastActive { get; set; }

    public string LastActiveDescription
    {
        get
        {
            var timeSpan = DateTime.Now - LastActive;
            if (timeSpan.Minutes == 0 && timeSpan.Seconds == 0)
                return "Just now";
            if (timeSpan.Minutes == 0)
                return timeSpan.Seconds + "s ago";
            return $"{timeSpan.Minutes}m  {timeSpan.Seconds}s ago";
        }
    }
}

Finally, in the page where you want to display the active users, display the results:

UserRepeater.DataSource = Global
    .ActiveUsersCache.GetActiveUsers().OrderByDescending(u => u.LastActive);
UserRepeater.DataBind();