Apply to class that executes a job in Hangfire. If a recurring job with this attribute is already running, a new one won't start

SkipWhenPreviousJobIsRunningAttribute.cs

using System;
using System.Collections.Generic;

using Hangfire.Client;
using Hangfire.Common;
using Hangfire.States;
using Hangfire.Storage;

/// <summary>
/// Makes sure that 2 (or more) same jobs will not be run twice at the same time.
/// If a job is already running, the new job will be skipped
/// </summary>
[AttributeUsage(AttributeTargets.All)]
public class SkipWhenPreviousJobIsRunningAttribute : JobFilterAttribute, IClientFilter, IApplyStateFilter
{
	public void OnCreating(CreatingContext filterContext)
	{
		var connection = (JobStorageConnection)filterContext.Connection;

		// We can't handle old storages
		if (connection == null) return;

		// We should run this filter only for background jobs based on 
		// recurring ones
		if (filterContext.Parameters.ContainsKey("RecurringJobId") == false) return;

		var recurringJobId = filterContext.Parameters["RecurringJobId"] as string;

		// RecurringJobId is malformed. This should not happen, but anyway.
		if (string.IsNullOrWhiteSpace(recurringJobId)) return;

		var running = connection.GetValueFromHash($"recurring-job:{recurringJobId}", "Running");
		if ("yes".Equals(running, StringComparison.OrdinalIgnoreCase))
		{
			filterContext.Canceled = true;
		}
	}

	public void OnStateApplied(ApplyStateContext context, IWriteOnlyTransaction transaction)
	{
		if (context.NewState is EnqueuedState)
		{
			var recurringJobId = JobHelper.FromJson<string>(context.Connection.GetJobParameter(context.BackgroundJob.Id, "RecurringJobId"));
			if (string.IsNullOrWhiteSpace(recurringJobId)) return;

			transaction.SetRangeInHash(
				$"recurring-job:{recurringJobId}",
				new[] { new KeyValuePair<string, string>("Running", "yes") });
		}
		else if (context.NewState.IsFinal)
		{
			var recurringJobId = JobHelper.FromJson<string>(context.Connection.GetJobParameter(context.BackgroundJob.Id, "RecurringJobId"));
			if (string.IsNullOrWhiteSpace(recurringJobId)) return;

			transaction.SetRangeInHash(
				$"recurring-job:{recurringJobId}",
				new[] { new KeyValuePair<string, string>("Running", "no") });
		}
	}

	public void OnCreated(CreatedContext filterContext)
	{
		// Method intentionally left empty.
	}

	public void OnStateUnapplied(ApplyStateContext context, IWriteOnlyTransaction transaction)
	{
		// Method intentionally left empty.
	}
}