How do I create a new thread to make pcap_loop() and gtk_main() compatible?

Question

These two functions are both infinite loops,

and the programe hangs once called in the same thread.

gtk_main(); 
...
pcap_loop(adhandle, 0, packet_handler, NULL);

When I click the "start" button,I want pcap to start working;And if I press the "stop" button,pcap stop.

How do I create a child thread and run pcap_loop(adhandle, 0, packet_handler, NULL); instead?

Answer 1

Take a look at the documentation for g_thread_create(). Also read this tutorial and this blog post for more information on multithreaded GTK programs.

Basically you'll want to call gtk_main() first when you've built your user interface and started your program. Then in the callback for the "start" button, create a new thread with g_thread_create() in which you call pcap_loop().

The "stop" button is a little more difficult since GLib doesn't allow you to interrupt a thread from a different thread. You'll have to create some signaling mechanism; for example, a boolean abort flag protected by a GMutex. In your stop button callback, lock the flag with g_mutex_lock(), set it, and unlock it with g_mutex_unlock(). In your packet_handler, also lock the flag, read it, and unlock it. If the flag was set, then call whatever it is you call to make pcap break out of the loop.

Answer 2

Unless I am missing something, your problem is that both GTK+ and libpcap are organized around events fired from a main loop. Without looking through the documentation, I don't know about GTK+, but there is another mode of operation for libpcap: You can use pcap_next() or pcap_next_ex() without giving up control over your program flow.

It should be possible to register a function that periodically calls one of these two functions using g_timeout_add() or g_idle_add(), removing the need to mess around with threads and mutex mechanisms altogether.