StreamReader await ReadLineAsync blocks execution

Question

I have the following code in a desktop application :

using (StreamReader reader = new StreamReader("path\\to\\file.csv"))
{
    string line;
    while (!reader.EndOfStream)
    {
        line = await reader.ReadLineAsync();
        string[] values = line.Split(',');
        double.TryParse(values[pointsIndex], out double points);
    }
}

The line line = await reader.ReadLineAsync() blocks the the program entirely and makes the application unresponsive. While debugging I noticed that it is runs 4 times and then blocks indefinitely.

This code is very simple and correct AFAIK. Why is it not working as expected?

score 1 · Answer 1 · edited Feb 07 '20 at 08:49

1

Try to change it to

using (StreamReader reader = new StreamReader("path\\to\\file.csv"))
{
    string line;
    while ((line = await reader.ReadLineAsync()) != null)
    {
     string[] values = line.Split(',');
     double.TryParse(values[pointsIndex], out double points);
    }
}

When it hits end - result will be null and terminate. See the relative documentation here

edited Feb 07 '20 at 08:49

Stefano Cavion

641
8
16

answered Feb 07 '20 at 08:44

Vytautas Plečkaitis

851
1
13
19

1

Doesn't work, still blocks indefinitely at ReadLineAsync. – Prabal Kajla Feb 07 '20 at 10:19
add Console.WriteLine(line); in while loop right before splitting to see where it stops. – Vytautas Plečkaitis Feb 07 '20 at 10:24
I used a break-point and debugging shows that it blocks at ```line = await reader.ReadLineAsync()``` – Prabal Kajla Feb 07 '20 at 10:26
I think there's issue somewhere else in code - the current code should work just fine. Alternatively you can try to change "using (StreamReader reader = File.OpenText("path\\to\\file.csv"))" and see if it helps. – Vytautas Plečkaitis Feb 07 '20 at 10:36
Also you might want to take a look at https://stackoverflow.com/questions/14526377/why-does-this-async-action-hang – Vytautas Plečkaitis Feb 07 '20 at 10:37
Thanks, this question helped a lot to understand the problem. It was a deadlock indeed. ```ReadLineAsync().ConfigureAwait(false)``` solves the problem. – Prabal Kajla Feb 07 '20 at 11:10
Glad it helped. – Vytautas Plečkaitis Feb 07 '20 at 11:35

StreamReader await ReadLineAsync blocks execution

1 Answers1