DisableMultipleQueuedItemsFilter.cs

public class DisableMultipleQueuedItemsFilter : JobFilterAttribute, IClientFilter, IServerFilter
{
    private static readonly TimeSpan LockTimeout = TimeSpan.FromSeconds(5);
    private static readonly TimeSpan FingerprintTimeout = TimeSpan.FromHours(1);

    public void OnCreating(CreatingContext filterContext)
    {
        if (!AddFingerprintIfNotExists(filterContext.Connection, filterContext.Job))
        {
            filterContext.Canceled = true;
        }
    }

    public void OnPerformed(PerformedContext filterContext)
    {
        RemoveFingerprint(filterContext.Connection, filterContext.Job);
    }

    private static bool AddFingerprintIfNotExists(IStorageConnection connection, Job job)
    {
        using (connection.AcquireDistributedLock(GetFingerprintLockKey(job), LockTimeout))
        {
            var fingerprint = connection.GetAllEntriesFromHash(GetFingerprintKey(job));

            DateTimeOffset timestamp;

            if (fingerprint != null &&
                fingerprint.ContainsKey("Timestamp") &&
                DateTimeOffset.TryParse(fingerprint["Timestamp"], null, DateTimeStyles.RoundtripKind, out timestamp) &&
                DateTimeOffset.UtcNow <= timestamp.Add(FingerprintTimeout))
            {
                // Actual fingerprint found, returning.
                return false;
            }

            // Fingerprint does not exist, it is invalid (no `Timestamp` key),
            // or it is not actual (timeout expired).
            connection.SetRangeInHash(GetFingerprintKey(job), new Dictionary<string, string>
            {
                { "Timestamp", DateTimeOffset.UtcNow.ToString("o") }
            });

            return true;
        }
    }

    private static void RemoveFingerprint(IStorageConnection connection, Job job)
    {
        using (connection.AcquireDistributedLock(GetFingerprintLockKey(job), LockTimeout))
        using (var transaction = connection.CreateWriteTransaction())
        {
            transaction.RemoveHash(GetFingerprintKey(job));
            transaction.Commit();
        }
    }

    private static string GetFingerprintLockKey(Job job)
    {
        return String.Format("{0}:lock", GetFingerprintKey(job));
    }

    private static string GetFingerprintKey(Job job)
    {
        return String.Format("fingerprint:{0}", GetFingerprint(job));
    }
    
    private static string GetFingerprint(Job job)
    {
        string parameters = string.Empty;
        if (job.Arguments != null)
        {
            parameters = string.Join(".", job.Arguments);
        }
        if (job.Type == null || job.Method == null)
        {
            return string.Empty;
        }
        var fingerprint = String.Format(
            "{0}.{1}.{2}",
            job.Type.FullName,
            job.Method.Name, parameters);

        return fingerprint;
    }

    void IClientFilter.OnCreated(CreatedContext filterContext)
    {
    }

    void IServerFilter.OnPerforming(PerformingContext filterContext)
    {
    }
}