C# endless list is filled and taken - BlockingCollection

Question

C# endless list is filled and taken - BlockingCollection

Markus Freitag 3,101

Hello,
I have a thread that receives data and buffers it in a list. Another thread that takes this data.

Task t1 = Task.Run(() =>  
                {  
                    bc.Add(1);  
                    bc.Add(2);  
                    bc.Add(3);  
                    bc.Add(4);  
                    bc.CompleteAdding();  
                });

This is endless, I don't know when it will be completed. I can't call bc.CompleteAdding();

I am looking for a good example to solve this requirement. Can you please help me with an example? Thank you in advance.

the block diagram

Answer 1

YASER SHADMEHR 771

Your scenario like ConcerentQueue without bounding. So you don't need to use CompleteAdding:

// Initialize Q and Cancelleation Token
var q = new BlockingCollection<int>();
var cts = new CancellationTokenSource();
var ct = cts.Token;

// Producer Thread.
var t1 = Task.Run(() =>
{
    int i = 0;
    do
    {
        q.Add(++i);
        Console.WriteLine(i + " is added to q");
    }
    while (!ct.IsCancellationRequested);
    Console.WriteLine("producer task is canceled");
}, ct);

// Consumer Thread.
var t2 = Task.Run(() =>
{
    do
    {
        while(q.Count > 0)
        {
            var result = q.Take();
            Console.WriteLine(result + " is removed from q");
        }
    }
    while (!ct.IsCancellationRequested);
    Console.WriteLine("consumer task is canceled");
}, ct);

To see in action, create a console app and copy the above code in the main function:

using System;
using System.Threading;
using System.Collections.Concurrent;
using System.Threading.Tasks;

namespace ConsoleApp1
{
    class Program
    {
        static void Main(string[] args)
        {
            // Copy above code here

            Console.Title = "Press any key to exit";
            Console.ReadLine();

            Console.Title = "Wait to Queue get empty";

            // Cancel t1 & t2
            cts.Cancel();

            // Wait for both thread to done
            Task.WaitAll(t1, t2);
        }
    }
}

See this example for using CompleteAdding.

Markus Freitag 3,101

Looks good. Small question again.

await is again missing.
When I write await in front of it, I get compiler errors.
What would be the correct syntax?

 private async Task BtnListEndless_Click(object sender, RoutedEventArgs e)
        {
            await Endless();

        }

        static async Task Endless()
        {
            // Initialize Q and Cancelleation Token
            var q = new BlockingCollection<int>();
            var cts = new System.Threading.CancellationTokenSource();
            var ct = cts.Token;

            // Producer Thread.
            var t1 = Task.Run(() =>
            {

Problems with the buttons, events. Any idea?

YASER SHADMEHR 771 Reputation points

2020-12-19T18:22:33.063+00:00

I need the whole code of the Endless function. Could you share the code and translate the error into English? Which version of .Net are you using?

Markus Freitag 3,101

Hello,

The XAML

Hello,
Now the code. Thanks for your help.

XAML File
Title="MainWindow" Height="450" Width="800">
<Grid>
<Button Name="btnBlockingList" Content="BlockingList" HorizontalAlignment="Left" Margin="541,114,0,0" VerticalAlignment="Top" Width="174" Height="56" Click="BtnBlockingList_ClickAsync"/>
<Button Name ="btnListEndless" Content="EndlessList" HorizontalAlignment="Left" Margin="556,229,0,0" VerticalAlignment="Top" Width="142" Height="67" Click="BtnListEndless_ClickAsync"/>
     </Grid>
 </Window>

YASER SHADMEHR 771 Reputation points

2020-12-21T18:40:10.017+00:00
@Markus Freitag The error said your Endless method is not async. when you marked a method as async you need at least have an await statement in the body method.

Replace Task.WaitAll(t1, t2); to below code:

// Wait for both thread with done await Task.WhenAll(t1, t2);
Markus Freitag 3,101 Reputation points

2020-12-22T06:42:39.18+00:00

Hello,
the code. Thanks in advance for your help.

I can't post the code here. Reason for picture.
Markus Freitag 3,101 Reputation points

2020-12-22T06:48:20.907+00:00

Return value is wrong

Markus Freitag 3,101

Hello,
//private async Task BtnListEndless_Click(object sender, RoutedEventArgs e)

private void BtnListEndless_ClickAsync(object sender, RoutedEventArgs e)
{
Endless();
}

static async Task Endless()
{
var q = new BlockingCollection<int>();
var cts = new System.Threading.CancellationTokenSource();
var ct = cts.Token;


var t1 = Task.Run(() =>
{
    int i = 0;
    do
    {
        q.Add(++i);
        Console.WriteLine(i + " is added to q");
    }
    while (!ct.IsCancellationRequested);
    Trace.WriteLine("producer task is canceled");
}, ct);

  var t2 = Task.Run(() =>
{
    do
    {
        while (q.Count > 0)
        {
            var result = q.Take();
            Console.WriteLine(result + " is removed from q");
        }
    }
    while (!ct.IsCancellationRequested);
    Console.WriteLine("consumer task is canceled");
}, ct);

Timon Yang-MSFT 9,511 Reputation points

2020-12-23T03:26:46.257+00:00

@Markus Freitag
There is no reason to set the return value of BtnListEndless_ClickAsync to Task, this event handler will not return information to any place, maybe you should set it to async void.
By the way, when you need to add information, it is best to add it to the original question, and then post a comment to remind members that you have made changes.
YASER SHADMEHR 771 Reputation points

2020-12-23T03:34:46.663+00:00

@Markus Freitag
If the Endless method just start two tasks, no need for async in the Endless signature.
Markus Freitag 3,101 Reputation points

2020-12-23T07:07:33.36+00:00

Can you make a sample with C# WPF desktop application?

When I need async?
Markus Freitag 3,101 Reputation points

2020-12-23T07:08:11.617+00:00

if the Endless method just start two tasks, no need for async in the Endless signature.

Can you make a sample with C# WPF desktop application?

When I need async?
YASER SHADMEHR 771 Reputation points

2020-12-26T04:43:03.623+00:00

@Markus Freitag We are going off the grid. I will provide you with an example, but please ask it in a different question. Also, remove unrelated comments here and mark the answer as accepted if it answers your first question. Don't forget to tag me in your next question.

C# endless list is filled and taken - BlockingCollection

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