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Mac Forum / Programming / CodeWarrior / May 2005Bug in alloc.c?
I'm getting an infinite loop in alloc.c, which is located in MSL/MSL_C/MSL_Common/Src. This is with CW 9.5. The function is allocate_from_var_pools. There is a do/while loop that searches for a block with the required size to allocate a block of memory. I got to this point through new, not malloc, in my own code. My new requests 16384 floats, which new translates to 65536 (four bytes per float) but which alloc first converts to 65552 before starting the do/while loop. After that, the loop starts trying to find a block. In other situations in my program, this allocation works, but in one reproducible situation the loop becomes infinite, meaning it neither finds a block, nor ever breaks out with a failed allocation. It should be noted that there is plenty of free memory on my computer, and we're only talking about 65k here. Any thoughts? ________________________________________________________________________ Keith Wiley kwiley@cs.unm.edu http://www.unm.edu/~keithw "Yet mark his perfect self-contentment, and hence learn his lesson, that to be self-contented is to be vile and ignorant, and that to aspire is better than to be blindly and impotently happy." -- Edwin A. Abbott, Flatland ________________________________________________________________________ > I'm getting an infinite loop in alloc.c, which is located in > MSL/MSL_C/MSL_Common/Src. This is with CW 9.5. The function is [quoted text clipped - 10 lines] > > Any thoughts? You've got my attention (I wrote this code). The most common cause of a situation like this is heap corruption from client code. However it is always possible that there is a bug in malloc. This malloc implementation is purposefully not robust in order to maximize performance and to make heap corruption bugs as visible as possible. The heap is a doubly linked and circular list of memory chunks. The behavior you describe indicates that the circularity of this chain has been compromised, perhaps it has been short circuited such that pool_obj->start_ no longer points anywhere into that circle. After making one circle around the chain, the loop should give up and go to the OS for more memory. If you could create a demo that you would be willing to mail me, I'd be happy to look at it. You could also try plugging in a debug new or malloc which might catch an earlier bug. There's one here you are welcome to try: http://home.twcny.rr.com/hinnant/MemoryManager/ -Howard Thanks. It sounds from your description like there is a fair chance my program is causing the problem at some earlier stage. I wouldn't be surprised if that were the case. I'll study it a little further before bothering you with it. Thanks. >> I'm getting an infinite loop in alloc.c, which is located in >> MSL/MSL_C/MSL_Common/Src. This is with CW 9.5. The function is [quoted text clipped - 32 lines] > > -Howard ________________________________________________________________________ Keith Wiley kwiley@cs.unm.edu http://www.unm.edu/~keithw "Yet mark his perfect self-contentment, and hence learn his lesson, that to be self-contented is to be vile and ignorant, and that to aspire is better than to be blindly and impotently happy." -- Edwin A. Abbott, Flatland ________________________________________________________________________ |
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