run multiple task and await for all tasks completes

Question

I need to run multiple task to access to database and to wait to all task finished to obtain the result and assign it to my viewmodel, i try many sample but i have never have the result, any help please, this my code

var model = new AggregationViewModel();
var loadDataTasks = new Task[]
{
    Task.Run(async () =>model.Alive =  await _repository.GetCountAsync<filter>(Predicate)),
    Task.Run(async () => model.Delay = await _repository.GetCountAsync<Flight>(predicate.And(x => x.Status == "refused")))
};
try
{
    await Task.WhenAll(loadDataTasks);
    foreach (var item in loadDataTasks)
    {

    }
}
catch (Exception ex)
{
}

Possible duplicate of [Running multiple async tasks and waiting for them all to complete](https://stackoverflow.com/questions/25009437/running-multiple-async-tasks-and-waiting-for-them-all-to-complete) — Volkmar Rigo, Mar 24 '19 at 18:03
I try same sample but my model.Delay and model.Alive always 0, and i don't know why — user1428798, Mar 24 '19 at 18:07
Your codce is missing the most essential part: how do you call this? Post the complete call chain. — H H, Mar 24 '19 at 18:10
"my main call" doesn't mean anything, you are still missing the most important parts. — H H, Mar 25 '19 at 17:07

Derviş Kayımbaşıoğlu · Accepted Answer · 2019-03-24T20:53:09.903

0

Check this out:

 var task1 = _repository.GetCountAsync<filter>(Predicate);
 var task2 = _repository.GetCountAsync<Flight>(predicate.And(x => x.Status == "refused"));

 await Task.WhenAll(task1, task2); //wait both tasks to finish

 model.Alive = await task1;
 model.Delay = await task2;

PS: the function, which the above code is placed, is needed to be async for the above scenario.

edited Mar 24 '19 at 20:53

answered Mar 24 '19 at 18:11

Derviş Kayımbaşıoğlu

28,492
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There's a typo: `WaitAll` -> `WhenAll` – tukaef Mar 24 '19 at 18:28
i can't add await before WaitAll and i had never the result – user1428798 Mar 24 '19 at 19:03

Ramin Bateni · Answer 2 · 2019-03-24T19:57:15.423

0

Try this code:

var model = new AggregationViewModel();

//----------------------------------------
var tasks = new List<Task<int>>();
//Add CountA
tasks.Add(_repository.GetCountAsync<filter>(Predicate));
//Add CountB
tasks.Add(_repository.GetCountAsync<Flight>(predicate.And(x => x.Status == "refused")));

//----------------------------------------
// Create a task with "allTasks" name to wait to complete all tasks
Task allTasks = Task.WhenAll(tasks);
try {
    // Wait to compelete "allTask"
     allTasks.Wait();
}
catch(AggregateException) 
{}

//----------------------------------------
//Working on the results

if (allTasks.Status == TaskStatus.RanToCompletion) {
   model.CountA=allTasks.Result[0]
   model.CountB=allTasks.Result[1]
}
// Display information on faulted tasks.
else {
    foreach (var t in tasks) {
        Console.WriteLine("Task {0}: {1}", t.Id, t.Status);
     }
}

edited Mar 24 '19 at 19:57

answered Mar 24 '19 at 18:56

Ramin Bateni

16,499
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what's t in the if please? – user1428798 Mar 24 '19 at 19:08
@user1428798, I have used `allTasks` in the condition section of the `if` block. Also `t` variable in `for` block points to each one of your defined tasks. Do you have any problem? – Ramin Bateni Mar 24 '19 at 19:42
in the first part is not defined in the if – user1428798 Mar 24 '19 at 19:50
Sorry I corrected it to `allTasks`. Check it now please. – Ramin Bateni Mar 24 '19 at 19:57

run multiple task and await for all tasks completes

2 Answers2