CODEWITHSUNDEEP
c#asp.net-coreasynchronous
Jakub michalenko
Jakub michalenko

Reputation: 23

c# asp.net core awaiting long running task stops after period of time

Recently I asked a question on StackOverflow about long running background Tasks in asp.net core. Since then I have tried everything from here https://learn.microsoft.com/cs-cz/aspnet/core/fundamentals/host/hosted-services?view=aspnetcore-5.0&tabs=visual-studio and if i do what I do it will just stop at some time. And it will stop even if I wrap it in IServiceProvider.CreateScope and await it. The only thing I still didn't try and I'm trying to avoid it, is creating dedicated .net application that would just read queue and do what it's supposed to do. And also I thing that it's overkill to create queue for it, I just want to run it in background asynchronously but it just stops. Sorry if it's some stupid bug but this is my first asp.net project and I'm fixing this problem for week now.

This is Queue version

public class QueuedHostedService : BackgroundService
    {
        private readonly IServiceProvider _serviceProvider;
        private readonly IBackgroundTaskQueue _queue;
        private readonly ILogger<QueuedHostedService> _logger;

        public QueuedHostedService(IServiceProvider serviceProvider, IBackgroundTaskQueue queue, ILogger<QueuedHostedService> logger)
        {
            _serviceProvider = serviceProvider;
            _queue = queue;
            _logger = logger;
        }

        protected override async Task ExecuteAsync(CancellationToken stoppingToken)
        {
            await BackgroundProcessing(stoppingToken);
        }

        private async Task BackgroundProcessing(CancellationToken stoppingToken)
        {
            while (!stoppingToken.IsCancellationRequested)
            {
                var workItem = await _queue.DequeueAsync(stoppingToken);

                try
                {
                    var scope = _serviceProvider.CreateScope();
                    var scrapeUrl = scope.ServiceProvider.GetRequiredService<IScopedScrapeUrl>();
                    // The scrape Sound Cloud Task is taking hours
                    await scrapeUrl.ScrapeSoundCloud(workItem);
                }catch(Exception ex)
                {
                    _logger.LogError($"Error occurred executing {nameof(workItem)},\n{ex}");
                }
            }
        }

        public override async Task StopAsync(CancellationToken stoppingToken)
        {
            _logger.LogInformation("Consume Scoped Scrape Url Hosted Service is stopping.");

            await base.StopAsync(stoppingToken);
        }

public class BackgroundScrapeQueue : IBackgroundTaskQueue
    {
        private readonly Channel<Scrape> _queue;
        private readonly ILogger<BackgroundScrapeQueue> _logger;

        public BackgroundScrapeQueue(ILogger<BackgroundScrapeQueue> logger)
        {
            var options = new BoundedChannelOptions(100)
            {
                FullMode = BoundedChannelFullMode.Wait
            };
            _queue = Channel.CreateBounded<Scrape>(options);
            _logger = logger;
        }

        public async ValueTask<Scrape> DequeueAsync(CancellationToken stoppingToken)
        {
            var workItem = await _queue.Reader.ReadAsync(stoppingToken);

            return workItem;
        }

        public async ValueTask QueueBackgroundWorkItemAsync(Scrape scrape)
        {
            if(scrape == null)
            {
                _logger.LogError("Invalid Scrape for queue");
                return;
            }

            await _queue.Writer.WriteAsync(scrape);
        }
    }

    public interface IBackgroundTaskQueue
    {
        ValueTask QueueBackgroundWorkItemAsync(Scrape scrape);

        ValueTask<Scrape> DequeueAsync(CancellationToken stoppingToken);
    }

Upvotes: 2

Views: 2023

Answers (1)

Stephen Cleary
Stephen Cleary

Reputation: 457272

it will just stop at some time. And it will stop even if I wrap it in IServiceProvider.CreateScope and await it.

Yes. That's the problem with in-memory background services. They can be stopped at any time, because they're hosted in an ASP.NET process that determines it's safe to shut down when requests are complete. ASP.NET will actually request a shutdown and then wait for a while for the services to complete, but there's also a timer where they'll be forced out if they don't complete within 10 minutes or so.

The bottom line is that shutdowns are normal. Any code that assumes it can run indefinitely in ASP.NET is inherently buggy.

The only thing I still didn't try and I'm trying to avoid it, is creating dedicated .net application that would just read queue and do what it's supposed to do.

That is the only reliable solution.

Upvotes: 2

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