using System.IO;
using System.Web.Mvc;

namespace MVC4Basic.Controllers
{
    public class HomeController : Controller
    {
        public ActionResult Index()
        {
            return View();
        }

        const int AMonth = 30 * 86400;

        [OutputCache(Duration = AMonth, VaryByParam = "name")]
        public ActionResult GetImage(string name)
        {
            name = Path.GetFileName(name);
            var path = Server.MapPath(string.Format("~/app_data/images/{0}", name));
            var content = System.IO.File.ReadAllBytes(path);
            return File(content, "image/png", name);
        }
    }
}

 <img src="@Url.Action("GetImage","Home", new { name = "test.png"})"/>

 Remote Address:127.0.0.1:5656
Request URL:http://localhost:10419/Home/GetImage?name=test.png
Request Method:GET
Status Code:200 OK

Response Headers
Cache-Control:public, max-age=2591916
Expires:Sat, 31 May 2014 12:45:55 GMT
Last-Modified:Thu, 01 May 2014 12:45:55 GMT

 Remote Address:127.0.0.1:5656
Request URL:http://localhost:10419/Home/GetImage?name=test.png
Request Method:GET
Status Code:304 Not Modified

Request Headers
If-Modified-Since:Thu, 01 May 2014 12:45:55 GMT

 Remote Address:127.0.0.1:5656
Request URL:http://localhost:10419/Home/GetImage?name=test.png
Request Method:GET
Status Code:200 OK (from cache)

 Remote Address:127.0.0.1:5656
Request URL:http://localhost:10419/Home/GetImage?name=test.png
Request Method:GET
Status Code:200 OK

Request Headers
If-Modified-Since:Thu, 01 May 2014 12:45:55 GMT

using System;
using System.IO;
using System.Net;
using System.Web.Mvc;

namespace MVC4Basic.Controllers
{
    public class HomeController : Controller
    {
        public ActionResult Index()
        {
            return View();
        }

        const int AMonth = 30 * 86400;

        [OutputCache(Duration = AMonth, VaryByParam = "name")]
        public ActionResult GetImage(string name)
        {
            name = Path.GetFileName(name);
            var path = Server.MapPath(string.Format("~/app_data/images/{0}", name));

            var lastWriteTime = System.IO.File.GetLastWriteTime(path);
            this.Response.Cache.SetLastModified(lastWriteTime.ToUniversalTime());

            var header = this.Request.Headers["If-Modified-Since"];
            if (!string.IsNullOrWhiteSpace(header))
            {
                DateTime isModifiedSince;
                if (DateTime.TryParse(header, out isModifiedSince) && isModifiedSince > lastWriteTime)
                {
                    return new HttpStatusCodeResult(HttpStatusCode.NotModified);
                }
            }

            var content = System.IO.File.ReadAllBytes(path);
            return File(content, "image/png", name);
        }
    }
}

 Remote Address:127.0.0.1:5656
Request URL:http://localhost:10419/Home/GetImage?name=test.png
Request Method:GET
Status Code:304 Not Modified

Request Headers
If-Modified-Since:Thu, 01 May 2014 13:43:32 GMT

    [AttributeUsage(AttributeTargets.Method, AllowMultiple = false)]
    public sealed class SetIfModifiedSinceAttribute : ActionFilterAttribute
    {
        public string Parameter { set; get; }
        public string BasePath { set; get; }

        public override void OnActionExecuting(ActionExecutingContext filterContext)
        {
            var response = filterContext.RequestContext.HttpContext.Response;
            var request = filterContext.RequestContext.HttpContext.Request;

            var path = getPath(filterContext);
            if (string.IsNullOrWhiteSpace(path))
            {
                response.StatusCode = (int)HttpStatusCode.NotFound;
                filterContext.Result = new EmptyResult();
                return;
            }

            var lastWriteTime = File.GetLastWriteTime(path);
            response.Cache.SetLastModified(lastWriteTime.ToUniversalTime());

            var header = request.Headers["If-Modified-Since"];
            if (string.IsNullOrWhiteSpace(header)) return;
            DateTime isModifiedSince;
            if (DateTime.TryParse(header, out isModifiedSince) && isModifiedSince > lastWriteTime)
            {
                response.StatusCode = (int)HttpStatusCode.NotModified;
                response.SuppressContent = true;
                filterContext.Result = new EmptyResult();
            }
        }

        string getPath(ActionExecutingContext filterContext)
        {
            if (!filterContext.ActionParameters.ContainsKey(Parameter)) return string.Empty;
            var name = filterContext.ActionParameters[Parameter] as string;
            if (string.IsNullOrWhiteSpace(name)) return string.Empty;

            var path = Path.GetFileName(name);
            path = filterContext.HttpContext.Server.MapPath(string.Format("{0}/{1}", BasePath, path));
            return !File.Exists(path) ? string.Empty : path;
        }
    }

        [SetIfModifiedSince(Parameter = "name", BasePath = "~/app_data/images/")]
        [OutputCache(Duration = AMonth, VaryByParam = "name")]
        public ActionResult GetImage(string name)
        {
            name = Path.GetFileName(name);
            var path = Server.MapPath(string.Format("~/app_data/images/{0}", name));
            var content = System.IO.File.ReadAllBytes(path);
            return File(content, "image/png", name);
        }

Today, we are announcing .NET Core 3.0 Preview 6. It includes updates for compiling assemblies for improved startup, optimizing applications for size with linker and EventPipe improvements. We’ve also released new Docker images for Alpine on ARM64. 

With the introduction of container support in Windows Server 2016, we open a world of opportunities that takes traditional monolithic applications on a journey to modernize them for better agility.

namespace Microsoft.Extensions.Hosting
{
    public interface IHostedService
    {
        Task StartAsync(CancellationToken cancellationToken);
        Task StopAsync(CancellationToken cancellationToken);
    }
}

using System;
using System.Threading;
using System.Threading.Tasks;
using Microsoft.Extensions.Hosting;
using Microsoft.Extensions.Logging;

namespace MvcTest
{
    public class SampleHostedService : IHostedService
    {
        private readonly ILogger<SampleHostedService> _logger;

        public SampleHostedService(ILogger<SampleHostedService> logger)
        {
            _logger = logger;
        }

        public async Task StartAsync(CancellationToken cancellationToken)
        {
            _logger.LogInformation("Starting Hosted service");

            while (!cancellationToken.IsCancellationRequested)
            {
                _logger.LogInformation("Hosted service executing - {0}", DateTime.Now);
                await Task.Delay(TimeSpan.FromSeconds(2), cancellationToken);
            }
        }

        public Task StopAsync(CancellationToken cancellationToken)
        {
            _logger.LogInformation("Stopping Hosted service");
            return Task.CompletedTask;
        }
    }
}

namespace MvcTest
{
    public class Startup
    {
        public void ConfigureServices(IServiceCollection services)
        {
            services.AddSingleton<IHostedService, SampleHostedService>();

services.AddHostedService<SampleHostedService>();

 public void Configure(IApplicationBuilder app, IHostingEnvironment env)

Startup.cs(82,56): error CS0104: 'IHostingEnvironment' is an ambiguous reference between
'Microsoft.AspNetCore.Hosting.IHostingEnvironment' and 'Microsoft.Extensions.Hosting.IHostingEnvironment'

D:\MvcTest>dotnet run
info: MvcTest.SampleHostedService[0]
      Starting Hosted service
info: MvcTest.SampleHostedService[0]
      Hosted service executing - 02/19/2019 14:45:10
info: MvcTest.SampleHostedService[0]
      Hosted service executing - 02/19/2019 14:45:12
info: MvcTest.SampleHostedService[0]
      Hosted service executing - 02/19/2019 14:45:14
Ctrl+C
Application is shutting down...
Hosting environment: Development
Content root path: D:\MvcTest
Now listening on: https://localhost:5001
Now listening on: http://localhost:5000
Application started. Press Ctrl+C to shut down.

namespace Microsoft.Extensions.Hosting
{
    public abstract class BackgroundService : IHostedService, IDisposable
    {
        protected BackgroundService();
        public virtual void Dispose();
        public virtual Task StartAsync(CancellationToken cancellationToken);
        public virtual Task StopAsync(CancellationToken cancellationToken);
        protected abstract Task ExecuteAsync(CancellationToken stoppingToken);
    }
}

namespace MvcTest
{
    public class PrinterHostedService : BackgroundService
    {
        private readonly ILogger<SampleHostedService> _logger;

        public PrinterHostedService(ILogger<SampleHostedService> logger)
        {
            _logger = logger;
        }

        protected override async Task ExecuteAsync(CancellationToken stoppingToken)
        {
            _logger.LogInformation("Starting Hosted service");

            while (!stoppingToken.IsCancellationRequested)
            {
                _logger.LogInformation("Hosted service executing - {0}", DateTime.Now);
                await Task.Delay(TimeSpan.FromSeconds(2), stoppingToken);
            }
        }
    }
}

namespace MvcTest
{
    public class Startup
    {
        public void ConfigureServices(IServiceCollection services)
        {
            services.AddHostedService<PrinterHostedService>();

D:\MvcTest>dotnet run
Hosting environment: Development
infoContent root path: D:\MvcTest
Now listening on: https://localhost:5001
Now listening on: http://localhost:5000
Application started. Press Ctrl+C to shut down.
: MvcTest.SampleHostedService[0]
      Starting Hosted service
info: MvcTest.SampleHostedService[0]
      Hosted service executing - 02/19/2019 15:00:23
info: MvcTest.SampleHostedService[0]
      Hosted service executing - 02/19/2019 15:00:25
info: MvcTest.SampleHostedService[0]
      Hosted service executing - 02/19/2019 15:00:27
Application is shutting down...
^C

using System;
using System.Threading;
using System.Threading.Tasks;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;

public abstract class ScopedBackgroundService : BackgroundService
{
    private readonly IServiceScopeFactory _serviceScopeFactory;

    public ScopedBackgroundService(IServiceScopeFactory serviceScopeFactory)
    {
        _serviceScopeFactory = serviceScopeFactory;
    }

    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
    {
        using (var scope = _serviceScopeFactory.CreateScope())
        {
            await ExecuteInScope(scope.ServiceProvider, stoppingToken);
        }
    }

    public abstract Task ExecuteInScope(IServiceProvider serviceProvider, CancellationToken stoppingToken);
}

 dotnet add package ncrontab

┌───────────── minute (0 - 59) 
│ ┌───────────── hour (0 - 23) 
│ │ ┌───────────── day of month (1 - 31) 
│ │ │ ┌───────────── month (1 - 12) 
│ │ │ │ ┌───────────── day of week (0 - 6) (Sunday to Saturday; 
│ │ │ │ │                                       7 is also Sunday on some systems) 
│ │ │ │ │ 
│ │ │ │ │ 
* * * * *

* * * * * *
- - - - - -
| | | | | |
| | | | | +--- day of week (0 - 6) (Sunday=0)
| | | | +----- month (1 - 12)
| | | +------- day of month (1 - 31)
| | +--------- hour (0 - 23)
| +----------- min (0 - 59)
+------------- sec (0 - 59)

using System;
using System.Threading;
using System.Threading.Tasks;
using Microsoft.Extensions.DependencyInjection;
using NCrontab;
using static NCrontab.CrontabSchedule;

public abstract class ScheduledScopedBackgroundService : ScopedBackgroundService
{
    private CrontabSchedule _schedule;
    private DateTime _nextRun;

    protected abstract string Schedule { get; }

    public ScheduledScopedBackgroundService(IServiceScopeFactory serviceScopeFactory)
     : base(serviceScopeFactory)
    {
        _schedule = CrontabSchedule.Parse(Schedule, new ParseOptions { IncludingSeconds = true });
        _nextRun = _schedule.GetNextOccurrence(DateTime.Now);
    }

    public override async Task ExecuteInScope(IServiceProvider serviceProvider, CancellationToken stoppingToken)
    {
        do
        {
            var now = DateTime.Now;
            if (now > _nextRun)
            {
                await ScheduledExecuteInScope(serviceProvider, stoppingToken);
                _nextRun = _schedule.GetNextOccurrence(DateTime.Now);
            }
            await Task.Delay(1000, stoppingToken); //1 second delay
        }
        while (!stoppingToken.IsCancellationRequested);
    }

    public abstract Task ScheduledExecuteInScope(IServiceProvider serviceProvider, CancellationToken stoppingToken);
}

using System;
using System.Threading;
using System.Threading.Tasks;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Logging;

public class MyScheduledTask : ScheduledScopedBackgroundService
{
    private readonly ILogger<MyScheduledTask> _logger;

    public MyScheduledTask(
        IServiceScopeFactory serviceScopeFactory,
        ILogger<MyScheduledTask> logger) : base(serviceScopeFactory)
    {
        _logger = logger;
    }

    protected override string Schedule => "*/10 * * * * *"; //Runs every 10 seconds

    public override Task ScheduledExecuteInScope(IServiceProvider serviceProvider, CancellationToken stoppingToken)
    {
        _logger.LogInformation("MyScheduledTask executing - {0}", DateTime.Now);
        return Task.CompletedTask;
    }
}

namespace MvcTest
{
    public class Startup
    {
        public void ConfigureServices(IServiceCollection services)
        {
            services.AddHostedService<MyScheduledTask>();

D:\MvcTest>dotnet run
Hosting environment: Development
Content root path: D:\MvcTest
Now listening on: https://localhost:5001
Now listening on: http://localhost:5000
Application started. Press Ctrl+C to shut down.
info: MyScheduledTask[0]
      MyScheduledTask executing - 02/19/2019 19:18:50
info: MyScheduledTask[0]
      MyScheduledTask executing - 02/19/2019 19:19:00
info: MyScheduledTask[0]
      MyScheduledTask executing - 02/19/2019 19:19:10
Application is shutting down...
^C