HttpClient - A task was cancelled

Question

It works fine when have one or two tasks however throws an error  A task was cancelled  when we have more than one task listed     List lt Task gt  allTasks   new List lt Task gt     allTasks Add        allTasks Add        Task WaitAll allTasks ToArray    configuration CancellationToken     private static Task lt T gt  HttpClientSendAsync lt T gt  string url  object data  HttpMethod method  string contentType  CancellationToken token        HttpRequestMessage httpRequestMessage   new HttpRequestMessage method  url       HttpClient httpClient   new HttpClient        httpClient Timeout   new TimeSpan Constants TimeOut        if  data    null                byte   byteArray   Encoding ASCII GetBytes Helper ToJSON data            MemoryStream memoryStream   new MemoryStream byteArray           httpRequestMessage Content   new StringContent new StreamReader memoryStream  ReadToEnd    Encoding UTF8  contentType              return httpClient SendAsync httpRequestMessage  ContinueWith task   gt                var response   task Result          return response Content ReadAsStringAsync   ContinueWith stringTask   gt                        var json   stringTask Result              return Helper FromJSON lt T gt  json                      Unwrap

User · Answer

var clientHttp   new HttpClient    clientHttp Timeout   TimeSpan FromMinutes 30     The above is the best approach for waiting on a large request  You are confused about 30 minutes  it s random time and you can give any time that you want   In other words  request will not wait for 30 minutes if they get results before 30 minutes  30 min means request processing time is 30 min  When we occurred error  Task was cancelled   or large data request requirements

User · Answer

I was using a simple call instead of async  As soon I added await  and made method async it started working fine  public async Task lt T gt  ExecuteScalarAsync lt T gt  string query  object parameter   null  CommandType commandType   CommandType Text  where T   IConvertible                       using  IDbConnection db   new SqlConnection  con                                 return await db ExecuteScalarAsync lt T gt  query  parameter  null  null  commandType

User · Answer

Another possibility is that the result is not awaited on the client side  This can happen if any one method on the call stack does not use the await keyword to wait for the call to be completed

User · Answer

in my  net core 3 1 applications I am getting two problem where inner cause was timeout exception  1  one is i am getting aggregate exception and in it s inner exception was timeout exception 2  other case was Task canceled exception My solution is catch  Exception ex                                if  ex InnerException is TimeoutException                                        ex   ex InnerException                                    else if  ex is TaskCanceledException                                        if   ex as TaskCanceledException  CancellationToken    null     ex as TaskCanceledException  CancellationToken IsCancellationRequested    false                                                ex   new TimeoutException  quot Timeout occurred quot                                                                            Logger Fatal string Format  quot Exception at calling  0    1  quot   url  ex Message   ex

User · Answer

In my situation  the controller method was not made as async and the method called inside the controller method was async   So I guess its important to use async await all the way to top level to avoid issues like these

User · Answer

Promoting  JobaDiniz s comment to an answer  Do not do the obvious thing and dispose the HttpClient instance  even though the code  quot looks right quot   async Task lt HttpResponseMessage gt  Method       using  var client   new HttpClient        return client GetAsync request      The same happens with C  s new RIAA syntax  slightly less obvious  async Task lt HttpResponseMessage gt  Method       using var client   new HttpClient      return client GetAsync request       Instead  cache a static instance of HttpClient for your app or library  and reuse it  static HttpClient client   new HttpClient     async Task lt HttpResponseMessage gt  Method       return client GetAsync request       The Async   request methods are all thread safe

User · Answer

There s 2 likely reasons that a TaskCanceledException would be thrown    Something called Cancel   on the CancellationTokenSource associated with the cancellation token before the task completed  The request timed out  i e  didn t complete within the timespan you specified on HttpClient Timeout    My guess is it was a timeout   If it was an explicit cancellation  you probably would have figured that out   You can be more certain by inspecting the exception   try       var response   task Result    catch  TaskCanceledException ex           Check ex CancellationToken IsCancellationRequested here         If false  it s pretty safe to assume it was a timeout

User · Answer

Another reason can be that if you are running the service  API  and put a breakpoint in the service  and your code is stuck at some breakpoint  e g Visual Studio solution is showing Debugging instead of Running    and then hitting the API from the client code  So if the service code a paused on some breakpoint  you just hit F5 in VS

User · Answer

I ran into this issue because my Main   method wasn t waiting for the task to complete before returning  so the Task lt HttpResponseMessage gt  myTask was being cancelled when my console program exited   The solution was to call myTask GetAwaiter   GetResult   in Main    from this answer

[c#] HttpClient - A task was cancelled?

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