c# - 尝试使用异步方法访问 Thread.CurrentPrincipal 时出现 ObjectDisposedException

Question

我对新的 async/await 东西还很陌生。但是，我有以下类(class):

public abstract class PluginBase
{
   //Using EF to store log info to database
   private EFContext _context = new EFContext();
   private int Id = 1;
   protected void LogEvent(string event, string details)
   {
       _context.LogEvents.Add(new LogItem(){
          PluginId = this.Id,
          Event = event,
          Details = details,
          User = Thread.CurrentPrincipal.Identity.Name
       });
   }
 }

public class Plugin : PluginBase
{
   public void Process()
   {
      CallWebService();
   }

   public async void CallWebService()
   {
       using(var http = new HttpClient())
       {
          ...
          var result = await http.PostAsync(memberURI, new StringContent(content, Encoding.UTF8,"application/json"));
          if(result.IsSuccessStatusCode)
             _status = "Success";
          else
             _status = "Fail";

          LogEvent("Service Call - " + _status,...);

       }
}

因此，想法是调用 Plugin.Process。它依次调用 CallWebService()。 CallWebService 对 http.PostAsync 进行异步调用。当我从该调用返回并尝试调用 base.LogEvent() 时，我收到一个 ObjectDisposedException，指出“安全句柄已关闭”。

我知道有一些事情正在发生，当等待完成时，必须运行该方法的其余代码。也许它正在其他线程或上下文中运行？如果是这种情况，如何在写入日志时获取当前用户？

感谢您对此的帮助。

编辑根据 Yuval 的回答，我进行了以下更改，它似乎工作正常。

public void Process()
{
    var task = CallWebService();
    task.Wait();
}
public async Task CallWebService(List<Member> members)
{
    using(var http = new HttpClient())
    {
       ...
       using(var result = await http.PostAsync(memberURI, new StringContent content, Encoding.UTF8, "application/json")))
       {
          if(result.IsSuccessStatusCode)
             _status = "Success";
          else
             _status = "Fail";
          LogEvent("Service Call - " + _status,...);
        }
    }
 }

Answer 1

When I return from that call and try to call base.LogEvent(), I get an ObjectDisposedException stating that "Safe Handle has been Closed".

那是因为在调用链的较高位置，有人正在处置您的插件对象，而该对象尚未真正完成异步操作。使用 async void 是在执行“即发即弃”操作。您实际上并没有在 Process 上await，因此调用它的任何人都假定它已完成并处理您的对象。

将您的async void方法更改为async Task，然后await它:

public Task ProcessAsync()
{
    return CallWebServiceAsync();
}

public async Task CallWebServiceAsync()
{
   using (var http = new HttpClient())
   {
      var result = await http.PostAsync(memberURI, 
                                        new StringContent(content,
                                                          Encoding.UTF8,
                                                          "application/json"));
      if (result.IsSuccessStatusCode)
         _status = "Success";
      else
         _status = "Fail";

      LogEvent("Service Call - " + _status,...);
   }
}

请注意，您还需要await ProcessAsync 位于调用堆栈更高层的位置。