C# Multithreading, GUI hangs while loading

Justincc

My Code below is using a backgroundWorker component. My entire GUI freezes while it loads the content tree from the database. The window even says (not responding) at the top. My desired result is to have a loading animation play while loading the data from the database... am I going at this wrong? Shouldn't the loading take place in the background, preventing the GUI from freezing up? Any ideas? ___________________________________________________________ private void bgWorker_DoWork(object sender, DoWorkEventArgs e) { LoadCompanies(); } private void bgWorker_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e) { ShowLoadingAnimation(false); } private void LoadCompanies(object sender, EventArgs e) { ShowLoadingAnimation(true); this.bgWorker.RunWorkerAsync(); } private delegate void LoadCompaniesDelegate(); public void LoadCompanies() { PROSOCO.Library.Companies.Criteria criteria = PROSOCO.Library.Companies.Criteria.GetCriteria(); BindingSource src = new BindingSource(); PROSOCO.Library.Companies.Nodes nodes = PROSOCO.Library.Companies.Nodes.GetNodes(criteria.NodeCriteria()); src.DataSource = nodes; if (pnlNavigation.InvokeRequired) { LoadCompaniesDelegate find = new LoadCompaniesDelegate(LoadCompanies); this.Invoke(find, new object[] { }); } else { pnlNavigation.ContentTree.ParentMember = "ParentId"; pnlNavigation.ContentTree.ValueMember = "Id"; pnlNavigation.ContentTree.DisplayMember = "Name"; pnlNavigation.ContentTree.PrefixMember = "CustomerNumber"; pnlNavigation.ContentTree.PostfixMember = "CityState"; pnlNavigation.ContentTree.DataSource = src; } _activeModule = "Companies"; }

Luc Pattyn

Hi, you seem aware of the fact that controls are not thread-safe, so you try to use InvokeRequired and Invoke(), but IMO there are some mistakes in the implementation\; the normal pattern is a method that ONLY contains something like if (InvokeRequired) Invoke(delegate) else do_whatever_needs_to_be_done_to_the_GUI Your public void LoadCompanies() method however contains stuff before the if; that stuff will execute twice, the second time on the GUI (bad for responsiveness); it also generates two BindingSource objects, only the second one will be used. I suggest you split the method in two parts, i.e. move the second half (the if-else) to a separate method, and apply the pattern to it, hence avoiding the first half to be executed twice (of which once on the GUI) :)

Luc Pattyn

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Justincc

It still has the same isse. I'm not sure I understood your suggestion, but I updated it as shown below. However, the gui still hangs while loading the companies. public void LoadCompanies() { if (pnlNavigation.InvokeRequired) { LoadCompaniesDelegate find = new LoadCompaniesDelegate(LoadCompanies); this.Invoke(find, new object[] { }); } else { PROSOCO.Library.Companies.Criteria criteria = PROSOCO.Library.Companies.Criteria.GetCriteria(); BindingSource src = new BindingSource(); PROSOCO.Library.Companies.Nodes nodes = PROSOCO.Library.Companies.Nodes.GetNodes(criteria.NodeCriteria()); src.DataSource = nodes; pnlNavigation.ContentTree.ParentMember = "ParentId"; pnlNavigation.ContentTree.ValueMember = "Id"; pnlNavigation.ContentTree.DisplayMember = "Name"; pnlNavigation.ContentTree.PrefixMember = "CustomerNumber"; pnlNavigation.ContentTree.PostfixMember = "CityState"; pnlNavigation.ContentTree.DataSource = src; } _activeModule = "Companies"; }

PhilDanger

I'm not quite sure what the LoadCompanies is supposed to be doing, but focus on this part:

  if (pnlNavigation.InvokeRequired) //checks to see if the current function is on the same thread as the object
  {
        LoadCompaniesDelegate find = new LoadCompaniesDelegate(LoadCompanies); //sets up a recursive call to LoadCompanies?
        this.Invoke(find, new object\[\] { }); //runs the LoadCompanies on the panel's thread
  }
  else
  {
        pnlNavigation.ContentTree.ParentMember = "ParentId";
        pnlNavigation.ContentTree.ValueMember = "Id";
        pnlNavigation.ContentTree.DisplayMember = "Name";
        pnlNavigation.ContentTree.PrefixMember = "CustomerNumber";
        pnlNavigation.ContentTree.PostfixMember = "CityState";
        pnlNavigation.ContentTree.DataSource = src;
  }

As you can see by the comments, the BackgroundWorker will indeed run LoadCompanies on its own thread. You then check for InvokeRequired -- since crossthreaded operations are illegal, this function returns true if the object is on another thread. If it is (which I'm guessing pnlNavigation is a GUI element on the GUI thread), you then call Invoke to call LoadCompanies, which forces it to run on the GUI thread! So you're back where you started, and you have to load from the database AGAIN!

Justincc

I changed LoadCompanies so as best I can tell, it isn't loading anything twice. It still has the same (not responding) issue while it loads all the records into the ContentTree. public void LoadCompanies() { if (pnlNavigation.InvokeRequired) { LoadCompaniesDelegate find = new LoadCompaniesDelegate(LoadCompanies); this.Invoke(find, new object[] { }); } else { PROSOCO.Library.Companies.Criteria criteria = PROSOCO.Library.Companies.Criteria.GetCriteria(); BindingSource src = new BindingSource(); PROSOCO.Library.Companies.Nodes nodes = PROSOCO.Library.Companies.Nodes.GetNodes(criteria.NodeCriteria()); src.DataSource = nodes; pnlNavigation.ContentTree.ParentMember = "ParentId"; pnlNavigation.ContentTree.ValueMember = "Id"; pnlNavigation.ContentTree.DisplayMember = "Name"; pnlNavigation.ContentTree.PrefixMember = "CustomerNumber"; pnlNavigation.ContentTree.PostfixMember = "CityState"; pnlNavigation.ContentTree.DataSource = src; } _activeModule = "Companies"; }

PhilDanger

This still makes it execute on the GUI thread. One idea would be to run everything but the actual GUI stuff in the background. When BackgroundWorker finishes, you can return the data that you need to load the GUI stuff (Binding Source) through the DoWorkEventArgs.Result (which gets sent to the RunWorkerCompletedEvent when it finish DoWork). You then cast the Result to a BindingSource and do the last portion of your code (after src.DataSource = nodes; ) in the GUI thread.

PhilDanger

Yes, the double loading was only one problem. Invoke forces it to run on the thread of the object that you called it from.

Luc Pattyn

No, that is not how I explained it; the else part executes on the GUI thread and hence must be fast. Take out everything that does not need to be there, and have it execute before you call public void LoadCompanies(). :)

Luc Pattyn

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Judah Gabriel Himango

Try changing the LoadCompanies method to this instead:

public void LoadCompanies(DoWorkEventArgs e)
{
PROSOCO.Library.Companies.Criteria criteria = PROSOCO.Library.Companies.Criteria.GetCriteria();

BindingSource src = new BindingSource();

PROSOCO.Library.Companies.Nodes nodes = PROSOCO.Library.Companies.Nodes.GetNodes(criteria.NodeCriteria());

src.DataSource = nodes;

e.Result = src;
}

Then change your RunWorkerCompleted handler to look like this:

private void bgWorker_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
{
BindingSource src = (BindingSource)e.Result;
pnlNavigation.ContentTree.ParentMember = "ParentId";
pnlNavigation.ContentTree.ValueMember = "Id";
pnlNavigation.ContentTree.DisplayMember = "Name";
pnlNavigation.ContentTree.PrefixMember = "CustomerNumber";
pnlNavigation.ContentTree.PostfixMember = "CityState";
pnlNavigation.ContentTree.DataSource = src;

ShowLoadingAnimation(false);

\_activeModule = "Companies";

}

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Justincc

I am new to C# so forgive me for not "just getting it" but this is what I have so far. I am doing something wrong because "BindingSource src = (BindingSource)e.Result;" Doesn't seem to be loading any data... Did I atleast get everything running in the background except the GUI stuff? Can you tell why I wouldn't be loading any data? Thanks in advance. private delegate object LoadCompaniesDelegate(); public object LoadCompanies() { BindingSource src = new BindingSource(); if (pnlNavigation.InvokeRequired) { LoadCompaniesDelegate find = new LoadCompaniesDelegate(LoadCompanies); this.Invoke(find, new object[] { }); } else { PROSOCO.Library.Companies.Criteria criteria = PROSOCO.Library.Companies.Criteria.GetCriteria(); PROSOCO.Library.Companies.Nodes nodes = PROSOCO.Library.Companies.Nodes.GetNodes(criteria.NodeCriteria()); src.DataSource = nodes; MessageBox.Show("Loaded Notes"); } return src; } private void bgWorker_DoWork(object sender, DoWorkEventArgs e) { e.Result = LoadCompanies(); } private void bgWorker_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e) { BindingSource src = (BindingSource)e.Result; pnlNavigation.ContentTree.ParentMember = "ParentId"; pnlNavigation.ContentTree.ValueMember = "Id"; pnlNavigation.ContentTree.DisplayMember = "Name"; pnlNavigation.ContentTree.PrefixMember = "CustomerNumber"; pnlNavigation.ContentTree.PostfixMember = "CityState"; pnlNavigation.ContentTree.DataSource = src; _activeModule = "Companies"; MessageBox.Show("Completed"); }

Justincc

It is still freezing the GUI. Let me know if I am doing this how you reccomended or not. Here is what I have: private void LoadCompanies(object sender, EventArgs e) { pnlNavigation.ShowLoader(true); this.bgWorker.RunWorkerAsync(); } private delegate object LoadCompaniesDelegate(); public void LoadCompanies(DoWorkEventArgs e) { PROSOCO.Library.Companies.Criteria criteria = PROSOCO.Library.Companies.Criteria.GetCriteria(); BindingSource src = new BindingSource(); PROSOCO.Library.Companies.Nodes nodes = PROSOCO.Library.Companies.Nodes.GetNodes(criteria.NodeCriteria()); src.DataSource = nodes; e.Result = src; } private void bgWorker_DoWork(object sender, DoWorkEventArgs e) { LoadCompanies(e); } private void bgWorker_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e) { BindingSource src = (BindingSource)e.Result; pnlNavigation.ContentTree.ParentMember = "ParentId"; pnlNavigation.ContentTree.ValueMember = "Id"; pnlNavigation.ContentTree.DisplayMember = "Name"; pnlNavigation.ContentTree.PrefixMember = "CustomerNumber"; pnlNavigation.ContentTree.PostfixMember = "CityState"; pnlNavigation.ContentTree.DataSource = src; pnlNavigation.ShowLoader(false); _activeModule = "Companies"; }

PhilDanger

Remove the --- if (pnlNavigation.InvokeRequired) { LoadCompaniesDelegate find = new LoadCompaniesDelegate(LoadCompanies); this.Invoke(find, new object[] { }); } else { -- Don't touch anything that has to do with a GUI element inside of your background worker DoWork for now... just keep what you have in RunWorkerCompleted. Currently it is taking the first path (InvokeRequired path), so the data won't be loaded into the BindingSource (since that is done in the Else) part.

PhilDanger

Stick in some debug statements to see where it is slowing down on.

Justincc

I get the (Not Responding) for a couple seconds when it gets to "pnlNavigation.ContentTree.DataSource = src;" This is a lot of data to load, however, I thought the background worker would handle that. Right?

Justincc

Thank you Phil. I still get the (Not Responding) for a couple seconds when it gets to "pnlNavigation.ContentTree.DataSource = src;" This is a lot of data to load. Since it is taking the most time, shouldn't that part be inside bgWorker_DoWork? ... but it cannot because it is updating the GUI ... so I don't konw what to do.

Justincc

What do you think about this explanation? The freezing is because the control is being filled out by the data source, and the only thread allowed to do that is the UI. So, if your data source is large there isn't a way around the 2 seconds pause... unless... You could manually fill out your control by looping over the data source yourself, and every 10 or so, do a DoEvents() call to keep the UI fresh.

Judah Gabriel Himango

To eliminate possibilities, temporarily comment all code inside RunWorkerCompleted handler. Does it still freeze?

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Judah Gabriel Himango

justin.moses wrote:

So, if your data source is large there isn't a way around the 2 seconds pause... unless...

If your data set is too large to be displayed all at once, your best bet is filling the dataset a few rows at a time, preferrably in the Application.Idle event handler. p.s. don't use DoEvents(). It's evil, trust me.

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