Question

我正在实施 Azure WebJob ，当由服务总线消息触发时，会执行异步API调用外部Web服务。执行Web请求后，我的webjob发生了一些奇怪的事情，并且在方法结束之前 inputMessage已经处理。下面是一个演示问题+输出的基本示例。

public async void HandleTestQueueMessage([ServiceBusTrigger("%TestQueue%")] BrokeredMessage inputMessage) {
    Console.WriteLine($"Received message {inputMessage.MessageId}.");

    Console.WriteLine("Starting web request.");
    await TestHttpClientAsync();
    Console.WriteLine("Finished web request.");

    await inputMessage.CompleteAsync(); // --> Exception occurs here
    Console.WriteLine($"Completed message {inputMessage.MessageId}.");
}

private async Task TestHttpClientAsync() {
    var httpClient = new HttpClient();
    var response = await httpClient.GetAsync("http://google.com");
    Console.WriteLine($"Got response, statuscode={response.StatusCode}.");
}

控制台输出：

Executing: 'ProblemTestHandler.HandleTestQueueMessage' - Reason: 'New ServiceBus message detected on 'TestQueue'.'
Received message a17cc4fce8c74b3c9f1b8f1a73b4ba1b.
Starting web request.
Executed: 'ProblemTestHandler.HandleTestQueueMessage' (Succeeded)
Got response, statuscode=OK.
Finished web request.

Unhandled Exception: System.ObjectDisposedException: BrokeredMessage has been disposed.
   at Microsoft.ServiceBus.Messaging.BrokeredMessage.ThrowIfDisposed()
   at Microsoft.ServiceBus.Messaging.BrokeredMessage.BeginComplete(AsyncCallback callback, Object state)
   at System.Threading.Tasks.TaskFactory`1.FromAsyncImpl(Func`3 beginMethod, Func`2 endFunction, Action`1 endAction, Object state, TaskCreationOptions creationOptions)
   at Microsoft.ServiceBus.Common.Parallel.TaskHelpers.CreateTask(Func`3 begin, Action`1 end, Object state)
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.GetResult()
   at Wkb.eInvoicing.Worker.Handlers.ProblemTestHandler.<HandleTestQueueMessage>d__1.MoveNext() in C:\Dev\eInvoicing\src\Wkb.eInvoicing.Worker\Handlers\ProblemTestHandler.cs:line 43
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.AsyncMethodBuilderCore.<>c.<ThrowAsync>b__6_1(Object state)
   at System.Threading.QueueUserWorkItemCallback.WaitCallback_Context(Object state)
   at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   at System.Threading.QueueUserWorkItemCallback.System.Threading.IThreadPoolWorkItem.ExecuteWorkItem()
   at System.Threading.ThreadPoolWorkQueue.Dispatch()
   at System.Threading._ThreadPoolWaitCallback.PerformWaitCallback()

正如您在输出中看到的那样，我的JobHost容器认为该方法在执行 httpClient.GetAsync（）方法后立即成功完成：

Starting web request.
Executed: 'ProblemTestHandler.HandleTestQueueMessage' (Succeeded)
Got response, statuscode=OK.

当我用非异步替代方法替换Web请求时（例如使用RestSharp），问题不会发生。任何想法可能是这个问题的根本原因？

Answer 1

你几乎不应该使用async void，除非你正在编写一个事件处理程序，你应该使用async Task代替，这让系统知道你的webjob还没有完成所以它不会尝试在资源完成之前强制关闭资源。

HttpClient GetAsync配置Webjob处理程序

1 个答案: