DebounceAttribute

DebounceAttribute.cs

public sealed class DebounceAttribute : JobFilterAttribute, IElectStateFilter
{
    private readonly string _resourceFormat;
    private readonly int _milliseconds;

    public DebounceAttribute(string resourceFormat, int milliseconds)
    {
        _resourceFormat = resourceFormat ?? throw new ArgumentNullException(nameof(resourceFormat));
        _milliseconds = milliseconds;
    }

    public void OnStateElection(ElectStateContext context)
    {
        // We are intercepting only transitions to the Processing state that happen,
        // when a worker picks up a background job and is about to process it.
        if (!(context.CandidateState is ProcessingState)) return;

        var connection = context.Connection as JobStorageConnection;
        if (connection == null) throw new NotSupportedException();

        var resource = String.Format(_resourceFormat, context.BackgroundJob.Job.Args.ToArray());
        var shouldRun = false;

        try
        {
            // Acquire a lock to prevent other workers to interfere between READ and WRITE operations
            // It's better to use TimeSpan.Zero as a lock timeout, but Hangfire storages don't yet support 
            // zero timeouts.
            using (connection.AcquireDistributedLock("debounce:lock", TimeSpan.FromMilliseconds(_milliseconds)))
            {
                var previousRun = JobHelper.DeserializeNullableDateTime(
                    connection.GetValueFromHash("debounce:resources", resource));

                var now = DateTime.UtcNow;

                if (previousRun == null || (now - previousRun.Value).TotalMilliseconds > _milliseconds)
                {
                    // If previous run date is missing (firing for the first time), or was too long ago,
                    // we should update the last run date/time and execute a job.
                    connection.SetRangeInHash("debounce:resources", new[]
                    {
                        new KeyValuePair<string, string>(resource, JobHelper.SerializeDateTime(now)),
                    });

                    shouldRun = true;
                }
            }
        }
        catch (DistributedLockTimeoutException)
        {
        }

        if (!shouldRun)
        {
            context.CandidateState = new DeletedState { Reason = "Deleted by the debounce filter" };
        }
    }
}