How to run multiple threads inside loop

Question

I am currently implementing a task that takes a lot of time. Basically, what I want to do is to run multiple tasks inside foreach loop. I tried using Parallel.ForEach its freezing my UI. I wanna be able to call like 10 uids at a time.

foreach (var uid in listBox2.Items)
              {
                  if (StopEmail) break;
                  Application.DoEvents();
                  string jsonstring = GetEmails(uid.ToString(), token);
                  if (jsonstring != null)
                  {
                      label6.Text = " Current UID: " + listBox2.Items.IndexOf(uid);
                      dynamic jsonResponse = JsonConvert.DeserializeObject(jsonstring);
                      string idstt = jsonResponse["email"];
                      if (idstt != null)
                      {
                          listBox3.Items.Add(idstt);
                          label4.Text = "Total Emails: " + listBox3.Items.Count.ToString();

                      }
                  }
              }

Here is my Parallel.ForEach Code:

var files = listBox2.Items.Cast<String>().ToList();
Parallel.ForEach(files, uid =>
{
    Application.DoEvents();
    string jsonstring = GetEmails(uid.ToString(), token);
    if (jsonstring != null)
    {
        this.Invoke(new MethodInvoker(delegate()
        {
            label6.Text = " Current UID: " + listBox2.Items.IndexOf(uid);
        }));

        dynamic jsonResponse = JsonConvert.DeserializeObject(jsonstring);
        string idstt = jsonResponse["email"];
        if (idstt != null)
        {
            this.Invoke(new MethodInvoker(delegate()
            {
                listBox3.Items.Add(idstt);
                label4.Text = "Total Emails: " + listBox3.Items.Count.ToString();
            }));
        }
    }
});

If this is freezing your UI, then you are running the outer part of the foreach on the UI thread. Try running it on a background worker so your UI thread is free to keep drawing. and then from the background thread try using parallel.ForEach — meganaut
– meganaut, Commented Dec 4, 2016 at 23:09
@meganaut can you please check my edit of parallel.foreach code. — Sherry Memon
– Sherry Memon, Commented Dec 4, 2016 at 23:14
@SherryMemon The problem is the method that parallel.foreach is running in is on the main or UI thread. Do a little research on backgroundWorkers to find out how to move that function OFF the main ui thread. — meganaut
– meganaut, Commented Dec 4, 2016 at 23:18

Enigmativity · Accepted Answer · 2016-12-04 23:35:54Z

2

Here's the approach I would take - use Microsoft's Reactive Framework (NuGet "System.Reactive.Windows.Forms").

Then you can do this:

var uids = listBox2.Item.Cast<String>().ToArray();

var query =
    from uid in uids.ToObservable()
    from jsonstring in Observable.Start(() => GetEmails(uid, token))
    where jsonstring != null
    select new { uid, jsonstring };

IDisposable subscription =
    query
        .ObserveOn(this)
        .Subscribe(x =>
        {
            label6.Text = " Current UID: " + listBox2.Items.IndexOf(x.uid);
            dynamic jsonResponse = JsonConvert.DeserializeObject(x.jsonstring);
            string idstt = jsonResponse["email"];
            if (idstt != null)
            {
                listBox3.Items.Add(idstt);
                label4.Text = "Total Emails: " + listBox3.Items.Count.ToString();
            }
        });

The slow part is in the GetEmails call so that is all nicely handled in the query.

The .ObserveOn(this) call marshals the code back to the UI thread for you so no messy .Invoke calls needed.

And finally, to end the computation early just call subscription.Dispose().

answered Dec 4, 2016 at 23:35

Enigmativity

117k12 gold badges101 silver badges184 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Sherry Memon Over a year ago

Yuhoo! Seems, awesome.

Dai · Accepted Answer · 2016-12-04 23:23:31Z

0

Wrap your Parallel.ForEach inside a Task.Run call:

var files = listBox2.Items.Cast<String>().ToList();
Task task = Task.Run( () => {

    Parallel.ForEach( files, uid =>
    {
        // remove the `Application.DoEvents()` call, it is unnecessary
        // ...
    }

} );

It may be a better design to instead return data from the ForEach method instead of calling .Invoke as well, that way you can use await and update the UI a single go when the ForEach is complete - but that depends on the nature of your loop and your desired UX.

answered Dec 4, 2016 at 23:23

Dai

158k31 gold badges314 silver badges436 bronze badges

4 Comments

Sherry Memon Over a year ago

How can I make it run like 10 uids at a time. I mean 10 tasks,

Dai Over a year ago

@SherryMemon Why 10 specifically? The Parallel.ForEach method will see how many hardware threads your computer has and run the correct number to ensure the list is processed optimally. So you must have a very good reason to override ForEach's thread count.

Sherry Memon Over a year ago

I wanna keep checking how many uids are checked and all that. that''s why I am updating UI.

Sherry Memon Over a year ago

it's doing a bad behavior like sometime it's jumping on uid 2776 and then jumps on uid 29.

Collectives™ on Stack Overflow

How to run multiple threads inside loop

2 Answers 2

1 Comment

4 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

1 Comment

4 Comments

Your Answer

Sign up or log in

Post as a guest

Related