DisableMultipleQueuedItemsFilter.cs

// Zero-Clause BSD (more permissive than MIT, doesn't require copyright notice)
// 
// Permission to use, copy, modify, and/or distribute this software for any purpose
// with or without fee is hereby granted.
// 
// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
// WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
// AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
// INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS
// OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER
// TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF
// THIS SOFTWARE.

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)
    {
    }
}

Thanks erwin-faceit. Updated.

using Hangfire.Client;
using Hangfire.Common;
using Hangfire.States;
using Hangfire.Storage;
using System;
using System.Collections.Generic;
using System.Globalization;
using System.Linq;
using System.Security.Cryptography;

namespace Hangfire.Filters
{
    public class DisableMultipleQueuedItemsFilter : JobFilterAttribute, IClientFilter, IApplyStateFilter
    {
        private static readonly TimeSpan LockTimeout = TimeSpan.FromSeconds(5);
        private static readonly CultureInfo EnUs = new CultureInfo("en-US");

        /// <summary>
        /// Convert arguments into a culture-aware string
        /// </summary>
        ///<see cref="https://gist.github.com/odinserj/a8332a3f486773baa009?permalink_comment_id=4048344#gistcomment-4048344"/><see>
        private static string ConvertArgument(object obj)
        {
            switch (obj)
            {
                case null:
                    return string.Empty;
                case string s:
                    return s;
                case DateTime dt:
                    return dt.ToString("o"); // ISO8601 date format
                default:
                    return (string)Convert.ChangeType(obj, typeof(string), EnUs); // And force the rest to US English
            }
        }

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

                if (fingerprint != null)
                {
                    // 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(fingerprintKey, new Dictionary<string, string>
                    {
                        { "Timestamp", DateTimeOffset.UtcNow.ToString("o") }
                    });

                return true;
            }
        }

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

        private static string GetFingerprintLockKey(string fingerprintKey)
        {
            return string.Format("{0}:lock", fingerprintKey);
        }

        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?.Args != null)
            {
                parameters = string.Join(".", job.Args.Select(ConvertArgument));
            }
            if (job?.Type == null || job.Method == null)
            {
                return string.Empty;
            }

            //https://gist.github.com/odinserj/a8332a3f486773baa009#gistcomment-1898401
            var payload = $"{job.Type.FullName}.{job.Method.Name}.{parameters}";
            var hash = SHA256.Create().ComputeHash(System.Text.Encoding.UTF8.GetBytes(payload));
            var fingerprint = Convert.ToBase64String(hash);
            return fingerprint;
        }

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

        public void OnCreated(CreatedContext filterContext)
        {
            //do nothing
        }


        public void OnStateApplied(ApplyStateContext context, IWriteOnlyTransaction transaction)
        {
            if (context.NewState.Name.Equals(Hangfire.States.SucceededState.StateName)
                || context.NewState.Name.Equals(Hangfire.States.FailedState.StateName))
            {
                RemoveFingerprint(context.Connection, context.BackgroundJob.Job);
            }
        }

        public void OnStateUnapplied(ApplyStateContext context, IWriteOnlyTransaction transaction)
        {
            // do nothing
        }
    }
}

⚠️⚠️⚠️ This works for the Enqueue only; Scheduled jobs will duplicate.

⚠️⚠️⚠️ This filter will break ContinueWith scenarios that expect a jobId string returned from BackgroundJobClient.Enqueue.

@mack0196, I believe you should check for the transition to Deleted state as well for fingerprint removal.

This solution sometimes is generating RedisTimeoutException upon fingerprint removal and in the error message it is something about
SUBSCRIBE fingerprint:60684f8fd3ad130e8c60210b41706448:lock:ev

Thanks mcastellano

Hello,
We experienced problem when passing CancellationToken into a job.
https://docs.hangfire.io/en/latest/background-methods/using-cancellation-tokens.html
In our case, when job was completed calculated hash was incorrect as Hangfire replaced it with null in Parameters.
To fix it we changed ConvertArgument method to ignore token.

@afelinczak

To fix it we changed ConvertArgument method to ignore token.

Please share your code changes

@HenrikHoyer Did you ever figure out the code @afelinczak was talking about

Hello, I missed the comment - sorry.
This is the fix we are using.

private static string ConvertArgument(object obj) => obj switch { CancellationToken => String.Empty, _ => JsonConvert.SerializeObject(obj) };

Hangfire replaced it with null in Parameters

Hello @afelinczak. What do you mean? CancellationToken is a struct, it can't be null. We must pass it as the default but it'll be replaced with real token in runtime. So it shouldn't be null anyway.

Btw. There is at least one more "special" parameter: PerformContext. It is not well documented but is is used by popular extension Hangfire.Console