在 C# 中延迟任务 - 数据库上下文已处置

Delaying a task in C# - db context disposed(在 C# 中延迟任务 - 数据库上下文已处置)

问题描述

我需要在某个时间执行某些代码(在我的 ASP .NET Core 项目中).

I have a situation where I need certain code to execute at a certain time (in my ASP .NET Core project).

我知道延迟任务不是一个很好的解决方案，但这就是我所拥有的，我想知道如何让它发挥作用:

I know that delaying a task is not a great solution, but this is what I have and I'd like to know how to make it work:

async Task MyMethod()
{
  // do something
  // Create a new thread that waits for the appropriate time
      TimeSpan time = dbAppointment.ScheduledOn - TimeSpan.FromMinutes(5.0) - DateTime.UtcNow;
      _ = Task.Delay(time).ContinueWith(async x => await 
          notificationManager.CreateReminder());
  // continue doing something
}

当我尝试运行代码时，它会在正确的时间进入应该执行的方法:

When I try to run the code, it enters the method that is supposed to be executed, at the right time:

public async Task CreateReminder() {}

但是当它尝试使用我使用 DI 注入到 NotificationManager 构造函数中的 dbContext 时失败，说明它已被释放.

but fails when it tries to use my dbContext which I injected using DI into the NotificationManager constructor, stating that it was disposed.

这就是流"；依赖项:

public class MyClass
{
  private readonly MyContext dbContext;
  private readonly INotificationManager notificationManager;
  public MyClass(MyContext context, INotificationManager nm) 
  { 
    dbContext = context;
    notificationManager = nm;
  }

  public async Task MyMethod() // the method shown in the snippet above
  { 
    // method does something using the dbContext

    _ = Task.Delay(time).ContinueWith(async x => await 
          notificationManager.CreateReminder());
  }
}

public class NotificationManager: INotificationManager
{
  private readonly MyContext dbContext;
  public NotificationManager(MyContext context) { dbContext = context;}
  public async Task CreateReminder() { // this method uses the dbContext}
}

startup.cs 中的 DI 设置:

DI setup in startup.cs:

services.AddDbContext<MyContext>(); 
services.AddScoped<INotificationManager, NotificationManager>();

推荐答案

选项

• 使用作业调度程序(如 Hangfire、Quartz.Net, Jobbr,...)
• 使用 后台服务 如果你的 .net 核心版本是 >= 2

• Use a job scheduler (Like Hangfire, Quartz.Net, Jobbr, ...)
• Use a background service if your .net core version is >= 2

在这两种情况下，您都需要在作业类中注入 DatabaseContext，否则您将收到 ObjectDisposedException.

In both cases you'll need to inject the DatabaseContext in the job class otherwise you'll receive an ObjectDisposedException.

当您需要横向扩展至多台机器时，您需要一个带有状态存储的作业服务器，例如 SQL Server、MSMQ、RabbitMQ、Redis...

When you need to scale-out to multiple machines you'll need a job server with a state store like SQL Server, MSMQ, RabbitMQ, Redis,...

Hangfire 示例

Sample with Hangfire

public class MyDelayJob
{
   private readonly MyContext dbContext;
   private readonly INotificationManager notificationManager;
   public MyDelayJob(MyContext context, INotificationManager nm)
   {
       dbContext= context;
       notificationManager = nm;
   }

   public async Task Run(/*parameters*/)
   {
      await notificationManager.CreateReminder()
   }
}

/*Shedule code in MyMethod
    IBackgroundJobClient can be injected
    you need to register MyDelayJob with your IOC container.
 */

backgroundJobClient.Schedule<MyDelayJob>(j => j.Run(), TimeSpan.FromSeconds(60))

请参阅 IBackgroundJobClient

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