Dialog box to abort a while-loop in C++/CLI - windows

Question

I have a while loop executed in a function. While the loop is executed, I would like to have a dialog box with an "Abort" button to show up on the screen on Windows. If I press the Abort button, the program would terminate the while loop. It's like a dialog which pops up when a file is copied. Could anybody suggest a simple way to do this with C++/CLI or something similar?
Since I don't have a lot of experience with C++/CLI, I would appreciate if you could provide me with code snippets or sample codes.

Answer 1

Using a separate thread is the modern way to do this, but there is another approach.
You can take the guts of your while loop and put them in an event handler. Arrange to have the message loop call this event handler again and again until the job it done (e.g., with a timer or idle processing). In the mean time, you can display a non-modal pop-up dialog. This is how printing used to work in the pre-emptive multitasking era. See SetAbortProc.
I'd recommend that second thread approach listed by others. I just wanted to point out that it's not the only way.

Answer 2

The construction of the while loop is the easy part. What makes it hard is you'll have to put the abort dialog in a different thread and then coordinate a flag in the while condition with the dialog. This is usually handled with semaphores which are known to be difficult to code without subtle side-effects.
The while loop, at a minimum, will need to have a mechanism that allows the event queue to get processed AND periodically checks for a change in the status of the abort semaphore.
//psuedo-code below
bool f_abort = false;
while (!f_abort)
{
do_partial_work();
f_abort = checkForAbort();
sleep(0); // don't want to lock the CPU
}
I'm not an expert in threads so I'll have to point you to other resources for what to do in checkForAbort().
Windows Forms Threading and Events - ListBox updates promptly but progressbar experiences huge delay
Win32 synchronization
Is putting thread on hold optimal?
Thread for Windows form

Answer 3

One simple (but poor) example could be this one:
#include "stdafx.h"
#include "windows.h"
#using <System.Windows.Forms.dll>
using namespace System;
using namespace System::Windows::Forms;
using namespace System::Threading;
DialogResult *res=new DialogResult(DialogResult::No);
void waitForUserAction()
{
while(*res==DialogResult::No)
{
*res=System::Windows::Forms::MessageBox::Show("Exit the loop ? YES/NO","TEST",
MessageBoxButtons::YesNo,MessageBoxIcon::Question);
if(*res==DialogResult::Yes)
Console::WriteLine(L"Exit by user");
}
}
int main()
{
ThreadStart ^start=gcnew ThreadStart(waitForUserAction);
Thread ^pThread=gcnew Thread(start);
int a=0;
pThread->Start();
while(*res!=DialogResult::Yes)
{
a=a+1;
Console::WriteLine(L"Loop processing here...{0}",a);
}
//pThread->Abort();
return 0;
}
You can check this article for more info on the topic...