How to run WndProc and pcap_loop callbacks

[notverybright]

After writing a console based app that uses Npcap libs to process packets, I've started on a Windows desktop app using VS 2022 C++ Win32 API which, at the moment, just displays packet source and destination IPs in a listbox. I have 2 buttons; Start and Stop which starts and stops the pcap_loop callback function.
When I click the Start button, packets are displayed in the Listbox OK, but clicking the Stop button takes a few clicks and a few seconds to respond and when it does, an exception occurs - Access violation at the pcap_loop function call.
I'm thinking this is because the pcap_loop is a callback function and is running at the same time as the WndProc callback function that processes Window messages, but correct me if I'm wrong.

WinMain has the standard code:
// Main message loop:
MSG msg;
while (GetMessage(&msg, NULL, 0, 0))
{
TranslateMessage(&msg);
DispatchMessage(&msg);
}

If my thinking is right, how can I run the 2 callback functions and gracefully stop the packet capture in the pcap_loop callback?

Thanks for any advice.

[salem_c]

Did you create a separate thread to handle pcap_loop?

> When I click the Start button, packets are displayed in the Listbox OK,
Generally, accessing the UI from a non-UI thread is a bad idea.
You might get short-term "it works", but eventually it all falls apart.

Your non-UI thread need to send some kind of message to the UI telling it 'here is a new pair of IP addresses'.

There are a couple of ways to do this.

1. Use a pipe
The pcap thread queues messages on the pipe, and the UI thread reads from it under the control of say a WM_TIMER.
https://learn.microsoft.com/en-us/wi...in32/ipc/pipes
https://learn.microsoft.com/en-us/wi...inmsg/wm-timer

2. Post messages
You create a new user message ID that your UI thread understands as meaning 'new IP pair'.
https://learn.microsoft.com/en-us/wi...threadmessagea

[2kaud]

For info about using threads with ui see:
http://www.flounder.com/uithreads.htm
http://www.flounder.com/workerthreads.htm

[notverybright]

Sorry for the delay in replying, I've been offline a bit. I haven't created a separate thread for pcap_loop yet, I was looking for advice on the best approach and I wanted opinions of threads before starting further development. I'll learn a bit about threads but start looking at pipes and how to post messages if they are a better option.

Thanks @salem_c and @2kaud for replying, I appreciate it.