External process stops everything else

piul

I have a windows Forms application that calls a mathematical calculations .exe

		superMinerProcess->Start();
		superMinerProcess->BeginOutputReadLine();	//Start reading the output
		while (!superMinerProcess->HasExited)
		{    //...   }

If I set a breakpoint after the Start(); the program only reaches it after the process has finished. I don't understand... Any idea?

Luc Pattyn

That is inconclusive. Where is this code located? what is in the while loop? what is it you are trying to achieve? :)

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piul

The application is a dialog that runs a long mathematical calculation (the external process, an independent executable) when pressing a Run button. Hence, this code is located within the buttonRun_Click function.

while (!superMinerProcess->HasExited)
{
if (processCancelled)
{
processCancelled = false;
break;
}
}

processCancelled is set to true in buttonCancel_Click. What I´m trying is to be able to kill the process when the user clicks on the Cancel button. I´ve tried writing superMinerProcess->Kill() in buttonCancel_Click but it won´t work because the Cancel button is just not clickable while the process is running. Here´s the rest of relevant code of the process

superMinerProcess = gcnew System::Diagnostics::Process;
superMinerProcess->StartInfo = gcnew System::Diagnostics::ProcessStartInfo;
superMinerProcess->StartInfo->RedirectStandardOutput = true;
superMinerProcess->StartInfo->UseShellExecute = false; //Necessary to redirect
superMinerProcess->StartInfo->FileName = SUPERMINER_EXE;
superMinerProcess->StartInfo->CreateNoWindow = true; //Don't open a new window for Process
//Arguments
superMinerProcess->StartInfo->Arguments = getArguments();
superMinerProcess->OutputDataReceived += gcnew System::Diagnostics::DataReceivedEventHandler (&Form1::StdoutHandler);

Luc Pattyn

OK, that is quite wrong for several reasons: 1. the while loop has no blocking calls, so it will spin at full speed, consuming all cycles of one (perhaps the only) core. If you must have a polling loop like that, at least slow it down by inserting say Thread.Sleep(100); However it is in general better to avoid a polling loop. 2. It is not OK to halt the main thread like that, as the whole GUI will freeze. If e.g. another window pops up on top of your app, and then goes away again, your app won't repaint itself. The correct approach would be: - to have a separate thread (I suggest a BackgroundWorker) which launches the process, captures its output, and waits for its termination; - to launch this thread from your button click handler (possibly also disabling said button, turning the cursor into a wait cursor, etc); - to have a delegate dealing with intermediate results (maybe showing them in a ListBox); - to have another delegate dealing with the termination of the process (restoring the GUI back to normal). BTW: said thread would not need a polling loop on superMinerProcess->HasExited, as it could use superMinerProcess->WaitForExit() :)

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piul

I like the idea of having the process in a different thread. It does work much better. However I have a problem when it comes to display in my form the text captured from the process. I have a delegate superMinerThreadWorkCompleted in charge of displaying the results.

void superMinerThreadWorkCompleted (System::Object^ sender, System::ComponentModel::DoWorkEventArgs^ e)
{
textBox = "Process text";
}

But I get the error C3352: superMinerThreadWorkCompleted(System::Object ^,System::ComponentModel::DoWorkEventArgs ^)' : the specified function does not match the delegate type 'void (System::Object ^,System::ComponentModel::RunWorkerCompletedEventArgs ^)' 1>Form1.cpp in the line

superMinerThread->RunWorkerCompleted += gcnew System::ComponentModel::RunWorkerCompletedEventHandler (&Form1::superMinerThreadWorkCompleted);

I can fix this by making the delegate static but then I cannot modify member class textBox. What could be the way around this?

Luc Pattyn

piul wrote:

DoWorkEventArgs

piul wrote:

RunWorkerCompletedEventArgs

these are different! the former is just wrong. :)

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piul

Changed the delegate to

void superMinerThreadWorkCompleted (System::Object^ sender,
System::ComponentModel::RunWorkerCompletedEventArgs^ e)
{}

and still got the same error 'void SuperMinerGUI::Form1::superMinerThreadWorkCompleted(System::Object ^,System::ComponentModel::RunWorkerCompletedEventArgs ^)' : the specified function does not match the delegate type 'void (System::Object ^,System::ComponentModel::RunWorkerCompletedEventArgs ^)' 1>Form1.cpp

Luc Pattyn

for non-static (instance) delegates, you need a constructor that takes two arguments, the first being this.

superMinerThread->RunWorkerCompleted += gcnew System::ComponentModel::RunWorkerCompletedEventHandler
(this, &Form1::superMinerThreadWorkCompleted);

:)

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Please use <PRE> tags for code snippets, they preserve indentation, improve readability, and make me actually look at the code.

piul

Cheers for that!