Tasks not being created?

Question

0.00/5 (No votes)

See more:

Hi all,

since VB wasn't an option to choose, I hope I'm still welcome here.

I've been trying to read a large number of particular entries from text files asynchroniously. Basically I'm now following the basic pattern from this Microsoft example.

Something seems to be wrong with my task creation: While, when debugging, 'entriesTasks' shows 53 tasks in the list right before entering the While-Loop, the loop is exited after the first line ('Dim finishedTask...') and 3 Threads end with Code 0.

Could someone please have a quick look on potential errors and guide me a bit with this? Just to mention it: The custom objects and methods should be ok (tested before) and the custom method, which is supposed to return 'Task(Of IEnumerable(Of FileData))', isn't even called i.e. a breakpoint not reached.

Thank you,
Michael

What I have tried:

VB

Dim entriesTasksQuery = From fi In LTODateilisten Select New Task(Of IEnumerable(Of FileData))(Function()
                                    Dim dlf As New DirListFile(fi)
                                    Return dlf.ReadFileEntriesAsync(fi)
                                  End Function)
Dim entriesTasks As List(Of Task(Of IEnumerable(Of FileData))) = entriesTasksQuery.ToList

While entriesTasks.Count > 0
     Dim finishedTask As Task(Of IEnumerable(Of FileData)) = Await Task.WhenAny(entriesTasks)
     entriesTasks.Remove(finishedTask)
     Dim entries As IEnumerable(Of FileData) = Await finishedTask
     Dim msg As String = $"{entries.Count} entries found."
     Debug.WriteLine(msg)
End While

Posted 23-Jul-23 5:12am

Sonhospa

Updated 23-Jul-23 5:27am

v3

Add a Solution

1 solution

Add a Solution

Add your solution here

Treat my content as plain text, not as HTML

Preview 0

…

Existing Members

Sign in to your account

...or Join us

Download, Vote, Comment, Publish.

Your Email
Password
Forgot your password?

Your Email
This email is in use. Do you need your password?
Optional Password

I have read and agree to the Terms of Service and Privacy Policy
Please subscribe me to the CodeProject newsletters

When answering a question please:

Read the question carefully.
Understand that English isn't everyone's first language so be lenient of bad spelling and grammar.
If a question is poorly phrased then either ask for clarification, ignore it, or edit the question and fix the problem. Insults are not welcome.
Don't tell someone to read the manual. Chances are they have and don't get it. Provide an answer or move on to the next question.

Let's work to help developers, not make them feel stupid.

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

Graeme_Grant · Accepted Answer · 2023-07-23T05:27:00

Quote:
Something seems to be wrong

This is like saying "My car won't start". We're like "did he turn the key, what happened?". You need to be specific.

When you ran the code did you get a thread exception error? That would be my first guess as you're doing unsafe thread operations. List is not thread- safe and entriesTasks.Remove(finishedTask) will be the culprit. You are better off using a ConcurrentBag and use TryTake to remove entries.

A rewrite would be:

VB

Dim entriesTasksQuery = From fi In LTODateilisten Select New Task(Of IEnumerable(Of FileData))(Function()
                                    Dim dlf As New DirListFile(fi)
                                    Return dlf.ReadFileEntriesAsync(fi)
                                  End Function)

Dim entriesTasks As New ConcurrentBag(Of Task(Of IEnumerable(Of FileData)))(entriesTasksQuery)

While entriesTasks.Count > 0
    Dim finishedTask As Task(Of IEnumerable(Of FileData)) = Await Task.WhenAny(entriesTasks)
    entriesTasks.TryTake(finishedTask)
    Dim entries As IEnumerable(Of FileData) = Await finishedTask
    Dim msg As String = $"{entries.Count} entries found."
    Debug.WriteLine(msg)
End While

This is untested but will fix the thread exception. But without you explaining in more detail, I am only guessing.

UPDATE

To force break on exceptions, go Debug > Windows > Exception Settings > click on "Common Language Runtime Exceptions" (must be a tick). This should catch it.

Update
Just did a quick sample and this works fine:

VB.NET

Imports System
Imports System.Collections.Generic
Imports System.Linq
Imports System.Threading.Tasks

Module Program
    Sub Main()
        Dim Tasks As New List(Of Task)()
        For i As Integer = 0 To 99
            Dim task As New DummyTask()
            Tasks.Add(task.ExecuteAsync())
        Next

        Console.WriteLine($"Running Tasks: {Tasks.Count}")

        While Tasks.Count > 0
            Dim completed As List(Of Task) = Tasks.Where(Function(task) task.IsCompleted).ToList()
            If completed.Any() = True Then
                For Each task As Task In completed.ToList()
                    'Console.WriteLine($"ID: {task.Id} is {task.Status}")
                    Tasks.Remove(task)
                    Console.WriteLine($"Running Tasks: {Tasks.Count}")
                Next
            End If
        End While

        Console.ReadLine()
    End Sub
End Module

Public Class DummyTask
    Private random As New Random()

    Public Async Function ExecuteAsync() As Task
        Await Task.Delay(random.Next(3000, 5000))
    End Function
End Class

and the output:

Running Tasks: 100
Running Tasks: 99
Running Tasks: 98
Running Tasks: 97
Running Tasks: 96
Running Tasks: 95
Running Tasks: 94
Running Tasks: 93
Running Tasks: 92
Running Tasks: 91
Running Tasks: 90
Running Tasks: 89
Running Tasks: 88
Running Tasks: 87
Running Tasks: 86
Running Tasks: 85
Running Tasks: 84
Running Tasks: 83
Running Tasks: 82
Running Tasks: 81
Running Tasks: 80
Running Tasks: 79
Running Tasks: 78
Running Tasks: 77
Running Tasks: 76
Running Tasks: 75
Running Tasks: 74
Running Tasks: 73
Running Tasks: 72
Running Tasks: 71
Running Tasks: 70
Running Tasks: 69
Running Tasks: 68
Running Tasks: 67
Running Tasks: 66
Running Tasks: 65
Running Tasks: 64
Running Tasks: 63
Running Tasks: 62
Running Tasks: 61
Running Tasks: 60
Running Tasks: 59
Running Tasks: 58
Running Tasks: 57
Running Tasks: 56
Running Tasks: 55
Running Tasks: 54
Running Tasks: 53
Running Tasks: 52
Running Tasks: 51
Running Tasks: 50
Running Tasks: 49
Running Tasks: 48
Running Tasks: 47
Running Tasks: 46
Running Tasks: 45
Running Tasks: 44
Running Tasks: 43
Running Tasks: 42
Running Tasks: 41
Running Tasks: 40
Running Tasks: 39
Running Tasks: 38
Running Tasks: 37
Running Tasks: 36
Running Tasks: 35
Running Tasks: 34
Running Tasks: 33
Running Tasks: 32
Running Tasks: 31
Running Tasks: 30
Running Tasks: 29
Running Tasks: 28
Running Tasks: 27
Running Tasks: 26
Running Tasks: 25
Running Tasks: 24
Running Tasks: 23
Running Tasks: 22
Running Tasks: 21
Running Tasks: 20
Running Tasks: 19
Running Tasks: 18
Running Tasks: 17
Running Tasks: 16
Running Tasks: 15
Running Tasks: 14
Running Tasks: 13
Running Tasks: 12
Running Tasks: 11
Running Tasks: 10
Running Tasks: 9
Running Tasks: 8
Running Tasks: 7
Running Tasks: 6
Running Tasks: 5
Running Tasks: 4
Running Tasks: 3
Running Tasks: 2
Running Tasks: 1
Running Tasks: 0

Everything works. However, if you have thread exception in the wait loop, refer to my first comment.