Multithreading cancellation

[airwot4]

I have the below code for a multithreaded winforms application. It
works successfully apart from the cancel function.

AppendLog2 has an out parameter which should return true if either of
two conditions are met (to cancel operation). This parameter is not
being passed back when AppendLog2 invokes itself, which is everytime
due to the operation.

Any ideas how I could better accomplish this? I followed this article:

http://msdn.microsoft.com/en-us/library/ms951109.aspx

Thanks



private void btnFSearch_Clic k_1(object sender, EventArgs e)
{
//Starts search operation or cancels running operation
....
switch (_state)
{
case RunState.Idle:
_state = RunState.Runnin g;
btnFSearch.Text = "Cancel";

FSearchDeleteDe legate delMain = new
FSearchDeleteDe legate(FileExis tsLoop);
delMain.BeginIn voke(arComputer s, txtFSearch.Text , null, null);
break;

case RunState.Runnin g:
_state = RunState.Cancel led;
btnFSearch.Enab led = false;
break;

case RunState.Cancel led:
MessageBox.Show ("Operation currently cancelling");
break;
}
}

public void FileExistsLoop( ArrayList arComputers, string
strFileSearchPa th)
{
//Loops through arComputers and logs back to main UI.
bool cancel = false;
AppendLog2("Che cking existance of " + strFileSearchPa th + " on " +
arComputers.Cou nt + " computers.", out cancel);
foreach (string strComputer in arComputers)
{
if (cancel) break;
if (Functions.Ping Test(strCompute r))
{
if (Functions.File Exists(strCompu ter, strFileSearchPa th))
AppendLog2(strC omputer + " = file exists", out cancel);
else
AppendLog2(strC omputer + " = file not found", out cancel);
}
else
AppendLog2(strC omputer + " is not responding to ping requests",
out cancel);
}
AppendLog2("*** Finished***", out cancel);
}

public void AppendLog2(stri ng log, out bool cancel)
{
if (txtOutput.Invo keRequired)
{
LogDelegate2 delInstance = new LogDelegate2(Ap pendLog2);
object inoutCancel = false;

Invoke(delInsta nce, new object[] { log, inoutCancel });

cancel = (bool)inoutCanc el;
}
else
{
//Check for cancel
cancel = (_state == RunState.Cancel led);

// Check for completion
if (cancel || (log == "***Finished*** "))
{
_state = RunState.Idle;
cancel = true;
...
}

...
}
return;
}

[Marc Gravell]

Re: Multithreading cancellation

Personally I'd look at BackgroundWorke r in this case, using CancelAsync
to request a cancel, with the worker code checking CancellationPen ding
to see if it should exit. This then handles all the grunge for you...

Marc

[qglyirnyfgfo@mailinator.com]

Re: Multithreading cancellation

Well, its kind of convoluted to explain but your problem basically
lies on your boxing and un-boxing of the Boolean (value type)
variable.

You box when you call “object inoutCancel = false” you un-box when you
call the “public void AppendLog2(stri ng log, out bool cancel)”
function etc.

I think you should do what Mark is suggesting but if you want to live
things the way they are you could at least change the Boolean cancel
variable to an object such as CancelEventArgs sot that you don’t have
to worry about boxing and un-boxing.

I hacked your exaple and made one of my own using CancelEventArgs so
that you can get the picture:

------------------------------

delegate void LogDelegate2(st ring log, CancelEventArgs cancel);

public partial class Form1 : Form
{
public Form1()
{
InitializeCompo nent();

new Thread(DoIt).St art();
}

void DoIt()
{
CancelEventArgs cancel = new CancelEventArgs ();
AppendLog2("aaa a", cancel);
}

public void AppendLog2(stri ng log, CancelEventArgs cancel)
{
if (this.InvokeReq uired)
{
LogDelegate2 delInstance = new LogDelegate2(Ap pendLog2);
Invoke(delInsta nce, new object[] { log, cancel });

bool cancelVal = cancel.Cancel;
}
else
{
cancel.Cancel = true;
}

return;
}
}


On Jun 6, 7:26 am, airwot4 <neale...@gmail .comwrote:

I have the below code for a multithreaded winforms application. It
works successfully apart from the cancel function.
>
AppendLog2 has an out parameter which should return true if either of
two conditions are met (to cancel operation). This parameter is not
being passed back when AppendLog2 invokes itself, which is everytime
due to the operation.
>
Any ideas how I could better accomplish this? I followed this article:http://msdn.microsoft.com/en-us/library/ms951109.aspx
>
Thanks
>
private void btnFSearch_Clic k_1(object sender, EventArgs e)
{
//Starts search operation or cancels running operation
...
  switch (_state)
  {
    case RunState.Idle:
      _state = RunState.Runnin g;
      btnFSearch.Text = "Cancel";
>
      FSearchDeleteDe legate delMain = new
FSearchDeleteDe legate(FileExis tsLoop);
      delMain.BeginIn voke(arComputer s, txtFSearch.Text , null, null);
      break;
>
    case RunState.Runnin g:
      _state = RunState.Cancel led;
      btnFSearch.Enab led = false;
      break;
>
    case RunState.Cancel led:
      MessageBox.Show ("Operation currently cancelling");
      break;
    }
>
}
>
public void FileExistsLoop( ArrayList arComputers, string
strFileSearchPa th)
{
//Loops through arComputers and logs back to main UI.
  bool cancel = false;
  AppendLog2("Che cking existance of " + strFileSearchPa th + " on " +
arComputers.Cou nt + " computers.", out cancel);
  foreach (string strComputer in arComputers)
  {
    if (cancel) break;
    if (Functions.Ping Test(strCompute r))
    {
      if (Functions.File Exists(strCompu ter, strFileSearchPa th))
        AppendLog2(strC omputer + " = file exists", out cancel);
      else
        AppendLog2(strC omputer + " = file not found", out cancel);
    }
    else
      AppendLog2(strC omputer + " is not responding to ping requests",
out cancel);
  }
  AppendLog2("*** Finished***", out cancel);
>
}
>
public void AppendLog2(stri ng log, out bool cancel)
{
  if (txtOutput.Invo keRequired)
  {
    LogDelegate2 delInstance = new LogDelegate2(Ap pendLog2);
    object inoutCancel = false;
>
    Invoke(delInsta nce, new object[] { log, inoutCancel });
>
    cancel = (bool)inoutCanc el;
   }
   else
   {
      //Check for cancel
      cancel = (_state == RunState.Cancel led);
>
      // Check for completion
      if (cancel || (log == "***Finished*** "))
      {
        _state = RunState.Idle;
        cancel = true;
        ...
      }
>
       ...
    }
  return;
>
>
>
}- Hide quoted text -
>
- Show quoted text -

[Marc Gravell]

Re: Multithreading cancellation

Re boxing - actually, I suspect it relates more to not getting the value
back out of the array here:

object inoutCancel = false;
Invoke(delInsta nce, new object[] { log, inoutCancel });
cancel = (bool)inoutCanc el;

But to be honest, until you posted I didn't look too much at the
specific code, preferring to lean towards a much simpler (and proven)
approach like BackgroundWorke r ;-p

Marc

[Marc Gravell]

Re: Multithreading cancellation

Ignore me - I misread the code anyways!

But it goes to show the point of using the simplest approach ;-p

Marc

[qglyirnyfgfo@mailinator.com]

Re: Multithreading cancellation

But to be honest, until you posted I didn't look too much at the

specific code, preferring to lean towards a much simpler (and proven)
approach like BackgroundWorke r ;-p

Yeah, post like this are real turn offs because they don’t compile and
are loooong so it’s hard to get someone to bother trying to figure
them out.

If only people posted “Short but complete examples”….. Oops, can I use
that phrase? Did Jon trade mark that already and I have to pay
royalties now?? :)

[airwot4]

Re: Multithreading cancellation

Thanks for the responses, I'll give BackgroundWorke r a try instead.

And sorry about the long post, I should have cut it down!