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Chipmunk Physics • View topic - Memory corruption in Magnets Sample

Memory corruption in Magnets Sample

Discuss any Chipmunk bugs here.

Memory corruption in Magnets Sample

Postby Extrawurst » Sun Dec 12, 2010 7:52 pm

I found two disturbing issues in the magnetsElectric.c sample in chipmunk 5.3.3:

1) minor: There is an obvious memory leak there which does not matter much until one tries to heavily benchmark the thing with a zillion of successive runs without restarting the whole application. All the allocations for the Singularities are not freed ever.

2) MAJOR: I dont know why the heck this works at all. This code heavily uses uninitialized float values for the angle arrays of the Singularity struct.
see line 228 where the property angle is used. These are not initilized correctly in both the methods "make_charged"(line 331) and "make_mix"(line 372). This was so hard to track down cause it led to very strange and hardly reproducable errors (endless loops in the hashFunctions cause the bounding boxes suddenly span the whole float value range). Anyway the really strange thing is that i just encountered that in the D version of the code which is an exact port of the original C version. Can anybody explain why the C version doesn't care about this ?
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Re: Memory corruption in Magnets Sample

Postby slembcke » Mon Dec 13, 2010 1:16 pm

I actually didn't write this demo. It was contributed by somebody else and I thought it was cool enough to include it. I've never actually noticed any memory leaks in it though.
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Re: Memory corruption in Magnets Sample

Postby Extrawurst » Thu Dec 16, 2010 4:48 am

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Re: Memory corruption in Magnets Sample

Postby Extrawurst » Thu Dec 16, 2010 4:55 am

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Re: Memory corruption in Magnets Sample

Postby slembcke » Thu Dec 16, 2010 9:38 am

Personally I rarely ever declare a variable without an initializer. It's just to easy to introduce bugs that way and I burned myself many times as a novice C programmer by trying to be clever about initializations. 95% of the time the bugs aren't apparent because you meant to initialize a value to something near 0, and there is 50/50 chance that you will get a very small garbage value from the stack.

Again, I've never actually looked closely at how that demo works. I just included it because it was neat. I guess I should actually clean it up some if I'm going to keep distributing it though.
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