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Return the results of Tasks - including the exceptions?

The following code run M1, M2, M3, M4 in parallel. Each method may raise exceptions. The method should return the results of the four async methods - either the int returned by methods or the Exceptions.
async Task<string> RunAll()
{
int m1result, m2result, m3result, m4result;
try
{
var m1task = M1();
var m2task = M2();
var m3task = M3();
var m4task = M4();
// await Task.WhenAll(new Task<int>[] { m1task, m2task, m3task, m4task });
m1result = await m1task;
m2result = await m2task;
m3result = await m3task;
m4result = await m4task;
}
catch (Exception ex)
{
// need to return the ex of the failed task. How?
}
// How to implement M1HasException, M2HasException, ... in the following lines?
var m1msg = M1HasException ? M1ExceptionMessage : m1result.ToString();
var m2msg = M2HasException ? M2ExceptionMessage : m2result.ToString();
var m3msg = M3HasException ? M3ExceptionMessage : m3result.ToString();
var m4msg = M4HasException ? M4ExceptionMessage : m4result.ToString();
return $"M1: {m1msg}, M2: {m2msg}, M3: {m3msg}, M4: {m4msg}";
}
How to capture the individual exceptions of the failed task?
For example, if only M2 threw an exception,
"M1: 1, M2: Excpetion...., M3: 3, M4: 4"

Each task has a Status and and Exception property.
You may want to see if it has faulted:
myTask.Status == TaskStatus.Faulted
Or if it has excepted:
if (myTask.Exception != null)
You can use ContinueWhenAll to run all the tasks and then check the status.
See the docs here.

As other answers/comments pointed out, one possible approach is by using ContinueWith or ContinueWhenAll. This is a clever trick because Task has the Exception property:
Gets the AggregateException that caused the Task to end prematurely.
If the Task completed successfully or has not yet thrown any
exceptions, this will return null.
Using ContinueWith whether a task completes successfully or not, it will be passed as the argument to the delegate function. From there you can check if an exception was thrown.
Task<string> GetStringedResult<T>(Task<T> initialTask)
{
return initialTask.ContinueWith(t => {
return t.Exception?.InnerException.Message ?? t.Result.ToString();
});
}
async Task<string> RunAll()
{
string m1result, m2result, m3result, m4result;
var m1task = GetStringedResult(M1());
var m2task = GetStringedResult(M2());
var m3task = GetStringedResult(M3());
var m4task = GetStringedResult(M4());
m1result = await m1task;
m2result = await m2task;
m3result = await m3task;
m4result = await m4task;
return $"M1: {m1result}, M2: {m2result}, M3: {m3result}, M4: {m4result}";
}

You can wrap the tasks inside a WaitAll and catch the AggregateException (docs),
try
{
Task.WaitAll(new[] { task1, task2 }, token);
}
catch (AggregateException ae)
{
foreach (var ex in ae.InnerExceptions)
//Do what ever you want with the ex.
}

Could you wrap each await in try-catch block and capture the exception message if any, seems feasible...
var results = new List<string>();
try { results.Add(await t1); } catch { results.Add("Exception"); };
try { results.Add(await t2); } catch { results.Add("Exception"); };
try { results.Add(await t3); } catch { results.Add("Exception"); };
return string.Join("|", results);
if you want to use WhenAll you could await for it and ignore exceptions and then do the same exercise as shown above to retrieve individual task results...
try { await Task.WhenAll(t1, t2, t3); } catch { };
// ^^^^^^^^^
// then same as ^ above

Method receiving Info from Teams causing later methods to crash

I have a method collecting user data from MS Teams, while this code works as intended, with this method added it makes a previously working method crash.
public async void GetUsers()
{
string teamId = "TeamsID";
string tenantId = "TenantID";
var connector = new ConnectorClient(new Uri(Instance.Activity.ServiceUrl));
members = await connector.Conversations.GetTeamsConversationMembersAsync(teamId, tenantId);
Instance.EmailList.Clear();
foreach (var member in members)
{
Instance.EmailList.Add(member.Email);
}
}
I believe that the Line:
members = await connector.Conversations.GetTeamsConversationMembersAsync(teamId, tenantId);
While receiving the user information, makes the bot think that a user is inputing, causing my later methods to trigger without user input, and crashing because there is no input or because the input if the chunk of data that is the user data.
This is just my theory and I may be incorrect.
The following is the method that crashes:
async Task ReplyToQuestions(IDialogContext context, IAwaitable<IMessageActivity> argument)
{
var AnswerHolder = await argument;
Answers.Add(AnswerHolder.Text);
Answers[AnswerCounter] = Answers[AnswerCounter].First().ToString().ToUpper() + Answers[AnswerCounter].Substring(1);
var isQuit = AnswerHolder.Text;
var isQuit2 = Regex.Match(isQuit, #"\b(Quit|quit|QUIT)\b").Value;
Regex rgx = new Regex(#"\b(Quit|quit|QUIT)\b");
if (rgx.IsMatch(isQuit2)) // checks for the user trying to quit/restart bot
{
await context.PostAsync(string.Format("Exiting current process. Restarting."));
context.Done(isQuit); // returns to the start of dialog (StartAsync)
}
else
{
if (QuestionCounter < 5)
{
await context.PostAsync(string.Format($"Question {QuestionCounter + 1}: {Question[QuestionCounter]}"));
}
AnswerCounter += 1;
QuestionCounter += 1;
if (AnswerCounter < 5)
{
context.Wait(ReplyToQuestions);
}
else if (AnswerCounter == 5)
{
PostToChannel($"{Name}'s answers to the questions are as follows: \n\nQuestion1 Answer: {Answers[0]} \n\nQuestion2 Answer: {Answers[1]} \n\n" +
$"Question3 Answer: {Answers[2]} \n\nQuestion4 Answer: {Answers[3]} \n\nQuestion5 Answer: {Answers[4]} \n\n", context);
await context.PostAsync(string.Format("Your answers have been posted to the 'What's Up' channel."));
AnswerCounter = 0;
QuestionCounter = 1;
context.Done(Answers[4]);
}
else
{
await context.PostAsync($"{AnswerCounter}");
await context.PostAsync(string.Format("Oh no! it appears something has gone wrong. please try re-entering your answers"));
AnswerCounter = 0;
QuestionCounter = 1;
context.Wait(ReplyToQuestions);
}
}
}
And the code that calls it:
async Task Choice(IDialogContext context, IAwaitable<IMessageActivity> argument) // this method recives and validates a question
{
var Choice = await argument;
var isQuit = Choice.Text;
var isQuit2 = Regex.Match(isQuit, #"\b(Quit|quit|QUIT)\b").Value;
Regex rgx = new Regex(#"\b(Quit|quit|QUIT)\b");
var isEnter = Regex.Match(isQuit, #"\b(Enter|ENTER|enter)\b").Value;
Regex rgx2 = new Regex(#"\b(Enter|ENTER|enter)\b");
var isReply = Regex.Match(isQuit, #"\b(Reply|REPLY|reply)\b").Value;
Regex rgx3 = new Regex(#"\b(Reply|REPLY|reply)\b");
GetUsers();
if (rgx.IsMatch(isQuit2)) // if the user choses to quit
{
await context.PostAsync(string.Format("Exiting current process. Restarting."));
context.Done(isQuit); // restarts the program, calls the first method
}
else if (rgx2.IsMatch(isEnter)) // if the user choses to quit
{
await context.PostAsync(string.Format("Please enter your custom question."));
context.Wait(EnterQuestion);
}
else if (rgx3.IsMatch(isReply)) // if the user choses to quit
{
Answers.Clear();
await context.PostAsync(string.Format("Please answer the following questions:"));
await context.PostAsync(string.Format($"Question 1: {Question[0]}"));
context.Wait(ReplyToQuestions);
}
else
{
await context.PostAsync(string.Format("sorry this was not a choice, try again."));
}
}
Does anyone know a way I can fix this? As I have spent 2 full days on this without success.

I'm not sure what error you are seeing. But, the method being used to retrieve conversation members has been deprecated: https://msdn.microsoft.com/en-us/microsoft-teams/botapis#net-example The note on that page should state:
you should migrate your code to use GetConversationMembersAsync(conversationId)
var connector = new ConnectorClient(new Uri(activity.ServiceUrl));
var members = await connector.Conversations.GetConversationMembersAsync(activity.Conversation.Id);

Async behaving sync while debugging?

Something is definitely flawed in my understanding of async/await. I want a piece of code named SaveSearchCase to run asynchronously in background.
I want it to be fired and forget about it and continue with the current method's return statement.
public IList<Entities.Case.CreateCaseOutput> createCase(ARC.Donor.Data.Entities.Case.CreateCaseInput CreateCaseInput, ARC.Donor.Data.Entities.Case.SaveCaseSearchInput SaveCaseSearchInput)
{
..........
..........
..........
var AcctLst = rep.ExecuteStoredProcedure<Entities.Case.CreateCaseOutput>(strSPQuery, listParam).ToList();
if (!string.IsNullOrEmpty(AcctLst.ElementAt(0).o_case_seq.ToString()))
{
Task<IList<Entities.Case.SaveCaseSearchOutput>> task = saveCaseSearch(SaveCaseSearchInput, AcctLst.ElementAt(0).o_case_seq);
Task t = task.ContinueWith(
r => { Console.WriteLine(r.Result); }
);
}
Console.WriteLine("After the async call");
return AcctLst;
}
And the SaveCaseSearch looks like
public async Task<IList<Entities.Case.SaveCaseSearchOutput>> saveCaseSearch(ARC.Donor.Data.Entities.Case.SaveCaseSearchInput SaveCaseSearchInput,Int64? case_key)
{
Repository rep = new Repository();
string strSPQuery = string.Empty;
List<object> listParam = new List<object>();
SQL.CaseSQL.getSaveCaseSearchParameters(SaveCaseSearchInput, case_key,out strSPQuery, out listParam);
var AcctLst = await rep.ExecuteStoredProcedureAsync<Entities.Case.SaveCaseSearchOutput>(strSPQuery, listParam);
return (System.Collections.Generic.IList<ARC.Donor.Data.Entities.Case.SaveCaseSearchOutput>)AcctLst;
}
But when I see the debugger createCase method waits for SaveCaseSearch to complete first and then only
it prints "After Async Call "
and then returns . Which I do not want definitely .
So which way is my understanding flawed ? Please help to make it run async and continue with current method's print and return statement .
UPDATE
I updated the SaveCaseSearch method to reflect like :
public async Task<IList<Entities.Case.SaveCaseSearchOutput>> saveCaseSearch(ARC.Donor.Data.Entities.Case.SaveCaseSearchInput SaveCaseSearchInput,Int64? case_key)
{
return Task.Run<IList<Entities.Case.SaveCaseSearchOutput>>(async (SaveCaseSearchInput, case_key) =>
{
Repository rep = new Repository();
string strSPQuery = string.Empty;
List<object> listParam = new List<object>();
SQL.CaseSQL.getSaveCaseSearchParameters(SaveCaseSearchInput, case_key, out strSPQuery, out listParam);
var AcctLst = await rep.ExecuteStoredProcedureAsync<Entities.Case.SaveCaseSearchOutput>(strSPQuery, listParam);
return (System.Collections.Generic.IList<ARC.Donor.Data.Entities.Case.SaveCaseSearchOutput>)AcctLst;
});
}
But there is something wrong with the params. It says
Error 4 A local variable named 'SaveCaseSearchInput' cannot be declared in this scope because it would give a different meaning to 'SaveCaseSearchInput', which is already used in a 'parent or current' scope to denote something else C:\Users\m1034699\Desktop\Stuart_V2_12042016\Stuart Web Service\ARC.Donor.Data\Case\Search.cs 43 79 ARC.Donor.Data

Well this saveCaseSearch() method runs synchronously in main thread and this is the main problem here. Instead of returning result with a task you should return Task with operation itself. Here is some simplified example :
Runs synchronously and waits 5 seconds
public IList<int> A()
{
var AcctLst = new List<int> { 0, 2, 5, 8 };
if (true)
{
Task<IList<int>> task = saveCaseSearch();
Task t = task.ContinueWith(
r => { Console.WriteLine(r.Result[0]); }
);
}
Console.WriteLine("After the async call");
return AcctLst;
}
// runs sync and in the end returns Task that is never actually fired
public async Task<IList<int>> saveCaseSearch()
{
Thread.Sleep(5000);
return new List<int>() { 10, 12, 16 };
}
Runs asynchronously - fires task & forgets :
public IList<int> A()
{
... same code as above
}
// notice that we removed `async` keyword here because we just return task.
public Task<IList<int>> saveCaseSearch()
{
return Task.Run<IList<int>>(() =>
{
Thread.Sleep(5000);
return new List<int>() { 10, 12, 16 };
});
}
Here is full code for this example

Against all that I believe in pertaining to "fire-and-forget" you can do this by writing your code this way:
public Task<SaveCaseSearchOutput> SaveCaseSearch(
SaveCaseSearchInput saveCaseSearchInput,
long? caseKey)
{
var rep = new Repository();
var query = string.Empty;
var listParam = new List<object>();
SQL.CaseSQL
.getSaveCaseSearchParameters(
saveCaseSearchInput,
caseKey,
out query,
out listParam);
return rep.ExecuteStoredProcedureAsync<SaveCaseSearchOutput>(
strSPQuery,
istParam);
}
And then if the place where you would like to fire it and log when it returns (which is really what you have -- so you're not forgetting about it), do this:
public IList<CreateCaseOutput> CreateCase(
CreateCaseInput createCaseInput,
SaveCaseSearchInput saveCaseSearchInput)
{
// Omitted for brevity...
var AcctLst =
rep.ExecuteStoredProcedure<CreateCaseOutput>(
strSPQuery,
listParam)
.ToList();
if (!string.IsNullOrEmpty(AcctLst.ElementAt(0).o_case_seq.ToString()))
{
SaveCaseSearch(saveCaseSearchInput,
AcctLst.ElementAt(0).o_case_seq)
.ContinueWith(r => Console.WriteLine(r.Result));
}
Console.WriteLine("After the async call");
return AcctLst;
}
The issue was that you were using async and await in the SaveSearchCase function, and this basically means that your code is the opposite of "fire-and-forget".
As a side note, you should really just use async and await, and avoid the "fire-and-forget" idea! Make your DB calls asynchronous and leverage this paradigm for what it's worth!
Consider the following:
The SaveCaseSearch call can stay as I have defined it above.
public Task<SaveCaseSearchOutput> SaveCaseSearch(
SaveCaseSearchInput saveCaseSearchInput,
long? caseKey)
{
var rep = new Repository();
var query = string.Empty;
var listParam = new List<object>();
SQL.CaseSQL
.getSaveCaseSearchParameters(
saveCaseSearchInput,
caseKey,
out query,
out listParam);
return rep.ExecuteStoredProcedureAsync<SaveCaseSearchOutput>(
strSPQuery,
istParam);
}
Then in your call to it, do this instead:
public async Task<IList<CreateCaseOutput>> CreateCase(
CreateCaseInput createCaseInput,
SaveCaseSearchInput saveCaseSearchInput)
{
// Omitted for brevity...
var AcctLst =
await rep.ExecuteStoredProcedureAsync<CreateCaseOutput>(
strSPQuery,
listParam)
.ToList();
if (!string.IsNullOrEmpty(AcctLst.ElementAt(0).o_case_seq.ToString()))
{
await SaveCaseSearch(saveCaseSearchInput,
AcctLst.ElementAt(0).o_case_seq)
.ContinueWith(r => Console.WriteLine(r.Result));
}
Console.WriteLine("After the async call");
return AcctLst;
}
This makes for a much better solution!

How to - Multiple Async tasks with timeout and cancellation

I would like to fire several tasks while setting a timeout on them. The idea is to gather the results from the tasks that beat the clock, and cancel (or even just ignore) the other tasks.
I tried using extension methods WithCancellation as explained here, however throwing an exception caused WhenAll to return and supply no results.
Here's what I tried, but I'm opened to other directions as well (note however that I need to use await rather than Task.Run since I need the httpContext in the Tasks):
var cts = new CancellationTokenSource(TimeSpan.FromSeconds(3));
IEnumerable<Task<MyResults>> tasks =
from url in urls
select taskAsync(url).WithCancellation(cts.Token);
Task<MyResults>[] excutedTasks = null;
MyResults[] res = null;
try
{
// Execute the query and start the searches:
excutedTasks = tasks.ToArray();
res = await Task.WhenAll(excutedTasks);
}
catch (Exception exc)
{
if (excutedTasks != null)
{
foreach (Task<MyResults> faulted in excutedTasks.Where(t => t.IsFaulted))
{
// work with faulted and faulted.Exception
}
}
}
// work with res
EDIT:
Following #Servy's answer below, this is the implementation I went with:
var cts = new CancellationTokenSource(TimeSpan.FromSeconds(3));
IEnumerable<Task<MyResults>> tasks =
from url in urls
select taskAsync(url).WithCancellation(cts.Token);
// Execute the query and start the searches:
Task<MyResults>[] excutedTasks = tasks.ToArray();
try
{
await Task.WhenAll(excutedTasks);
}
catch (OperationCanceledException)
{
// Do nothing - we expect this if a timeout has occurred
}
IEnumerable<Task<MyResults>> completedTasks = excutedTasks.Where(t => t.Status == TaskStatus.RanToCompletion);
var results = new List<MyResults>();
completedTasks.ForEach(async t => results.Add(await t));

If any of the tasks fail to complete you are correct that WhenAll doesn't return the results of any that did complete, it just wraps an aggregate exception of all of the failures. Fortunately, you have the original collection of tasks, so you can get the results that completed successfully from there.
var completedTasks = excutedTasks.Where(t => t.Status == TaskStatus.RanToCompletion);
Just use that instead of res.

I tried you code and it worked just fine, except the cancelled tasks are in not in a Faulted state, but rather in the Cancelled. So if you want to process the cancelled tasks use t.IsCanceled instead. The non cancelled tasks ran to completion. Here is the code I used:
public static async Task MainAsync()
{
var urls = new List<string> {"url1", "url2", "url3", "url4", "url5", "url6"};
var cts = new CancellationTokenSource(TimeSpan.FromSeconds(3));
IEnumerable<Task<MyResults>> tasks =
from url in urls
select taskAsync(url).WithCancellation(cts.Token);
Task<MyResults>[] excutedTasks = null;
MyResults[] res = null;
try
{
// Execute the query and start the searches:
excutedTasks = tasks.ToArray();
res = await Task.WhenAll(excutedTasks);
}
catch (Exception exc)
{
if (excutedTasks != null)
{
foreach (Task<MyResults> faulted in excutedTasks.Where(t => t.IsFaulted))
{
// work with faulted and faulted.Exception
}
}
}
}
public static async Task<MyResults> taskAsync(string url)
{
Console.WriteLine("Start " + url);
var random = new Random();
var delay = random.Next(10);
await Task.Delay(TimeSpan.FromSeconds(delay));
Console.WriteLine("End " + url);
return new MyResults();
}
private static void Main(string[] args)
{
MainAsync().Wait();
}

Strange behavior of Parallel.ForEach

I have the following code:
Parallel.ForEach(xRoot.Elements("key"), xKey =>
{
int id = int.Parse(xKey.Attribute("id").Value);
string code = xKey.Attribute("code").Value;
AccountStatus accountStatus = SomeClient.GetAccountStatusAsync(id, code).Result;
);
The count of xRoot.Elements("key") is 3, but ForEach iterates only 2 times. Why?

Mixing Parallel.ForEach and async/await isn't a good idea. You don't need async methods to execute in parallel, you need them to execute concurrently. Your current code uses threadpool threads to block on an I/O operation, missing the advantage of an async api.
Try this:
var codeIds = xRoot.Elements("key").Select(xKey => new { Id = int.Parse(xKey.Attribute("id").Value, Code = xKey.Attribute("code").Value });
var codeTasks = codeIds.Select(x => SomeClient.GetAccountStatusAsync(x.Id, x.Code));
await Task.WhenAll(codeTasks);

Try:
Parallel.ForEach(xRoot.Elements("key"), async xKey =>
{
int id = int.Parse(xKey.Attribute("id").Value);
string code = xKey.Attribute("code").Value;
AccountStatus accountStatus = await SomeClient.GetAccountStatusAsync(id, code);
);
Or:
Parallel.ForEach(xRoot.Elements("key"), xKey =>
{
try
{
int id = int.Parse(xKey.Attribute("id").Value); // maybe null reference here?
string code = xKey.Attribute("code").Value; // or here?
AccountStatus accountStatus = SomeClient.GetAccountStatusAsync(id, code).Result; // or even here?
}
catch (Exception ex)
{
throw; // add here a breakpoint and check what's up by checking 'ex' object
}
);