.NET Core 中基於 IHostedService 實現后台定時任務

.NET Core 2.0 引入了 IHostedService ，基於它可以很方便地執行后台任務，.NET Core 2.1 則錦上添花地提供了 IHostedService 的默認實現基類 BackgroundService ，在這篇隨筆中分別用 Web 與 Console 程序體驗一下。

首先繼承 BackgroundService 實現一個 TimedBackgroundService

public class TimedBackgroundService : BackgroundService
{
    private readonly ILogger _logger;
    private Timer _timer;

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

    protected override Task ExecuteAsync(CancellationToken stoppingToken)
    {
        _timer = new Timer(DoWork, null, TimeSpan.Zero, TimeSpan.FromSeconds(5));
        return Task.CompletedTask;
    }

    private void DoWork(object state)
    {
        _logger.LogInformation($"Hello World! - {DateTime.Now}");
    }

    public override void Dispose()
    {
        base.Dispose();
        _timer?.Dispose();
    }
}

在 ASP.NET Core Web 程序中執行這個后台定時任務只需在 Startup 的 ConfigureServices 注冊 TimedBackgroundService 即可：

public void ConfigureServices(IServiceCollection services)
{
    services.AddHostedService<TimedBackgroundService>();
}

然后只要站點啟動，就會定時輸出日志：

Now listening on: http://localhost:5000
Application started. Press Ctrl+C to shut down.
info: BackgroundServiceSample.Services.TimedBackgroundService[0]
      Hello World! - 9/14/2018 17:48:02
info: BackgroundServiceSample.Services.TimedBackgroundService[0]
      Hello World! - 9/14/2018 17:48:07
info: BackgroundServiceSample.Services.TimedBackgroundService[0]
      Hello World! - 9/14/2018 17:48:12

接下來在控制台程序中體驗一下。
基於 Generic Host 實現如下的控制台程序，也是執行在 ConfigureServices 中注冊一下 TimedBackgroundService 。

class Program
{
    public static async Task Main(string[] args)
    {
        var builder = new HostBuilder()
            .ConfigureLogging(logging =>
            {
                logging.AddConsole();
            })
            .ConfigureServices((hostContext, services) =>
            {
                services.AddHostedService<TimedBackgroundService>();
            });

        await builder.RunConsoleAsync();
    }
}

dotnet run 運行程序后 TimedBackgroundService 定時輸出了日志：

info: BackgroundServiceSample.Services.TimedBackgroundService[0]
      Hello World! - 9/14/2018 17:59:37
info: BackgroundServiceSample.Services.TimedBackgroundService[0]
      Hello World! - 9/14/2018 17:59:42
info: BackgroundServiceSample.Services.TimedBackgroundService[0]
      Hello World! - 9/14/2018 17:59:47

體驗完成。