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Class and Thread Problems

Started by Last Attacker Aug 4, 2006 at 5:49 PM 4 replies 650+ views

Original Post

Aug 4, 2006 at 5:49 PM

Hi everyone! I am writing a ray tracer in C plus plus with wxWidgets and I have a class with 2 virtual functions and 2 classes deriving from that class implementing those virtual functions. The top class is CObject and the lower classes are CSphere and CPlane. Now I wanted to use a thread (maybe 2 later [wink]) to render my scene. I have an array of (CObject *)s which contains CSphere and CPlane objects. When I call the virtual function to execute (you know via polymorphism) from my running thread then the program bombs out with a segmentation fault. I can access the other functions in the CObject class except the virtual functions. I think that threads have a problem with the virtual table or something. I am using the wxThread class for my thread. EDIT: I have done this without threads and it worked 100%, I just want to move over to threads sothat I can implement a progress bar and maybe try to let 2 threads render my scene (maybe it'll be faster, I'll see). Also, I tried this on wxWidgets 2.6.2 & 2.6.3 Anyone know what could be the problem? Thanks [Edited by - Last Attacker on August 5, 2006 2:35:25 AM]

twix

Aug 4, 2006 at 11:11 PM

wxWidgets is not thread-safe. If you're making any GUI calls from threads other than the one the wxWidgets event loop is running in, that's likely the reason for the crashes.

Last Attacker

Aug 5, 2006 at 1:47 AM

Well, I'm still busy with my app, so when I click on File->New, it creates a thread, and then is supposed to render my scene. Currently I only have 1 thread doing this.
I'm also not accessing any widgets in my thread, just my arrays and buffers.

I'm using MingW 3.4.4 as my compiler.

Last Attacker

Aug 5, 2006 at 2:32 AM

I saw that even when I remove the 'virtual' keywords and just put CSpheres in the array and cast that object in the array of (CObject *)s to a (CSphere *) and still call that specific funtion, it still bombs out.
So I guess we can scratch out virtual functions to be the problem. Maybe its inherited classes that presents a problem or something.

Last Attacker

Aug 5, 2006 at 4:17 AM

I found out what the problem was!
Thank God that it wasn't a thread problem. I just forgot to dynamically allocate my arrays, etc.
It didn't occur to me that when a thread runs that the local variables are going to "go extinct" while the thread is running so I just "new"ed them all and destroyed them when the thread ended.

Thanks for everyone's replies!

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