> Garbage collection doesn't use a stack. It uses a "heap", which is in > the abstract a collection of memory blocks of different lengths, > divided into two lists, generally represented as linked lists: > > 1. A list of blocks that are free and may be used to store new data > > 2. A list of blocks that are in use, or haven't been freed (yet)
Is this all that a heap is or is there more to it ? I have been looking for simple but complete explanation of heap for a while and not gotten to it. I think I am looking for a stack allocation on the same pattern. In a disk, a file is fragmented in many contiguous blocks and is accessed automatically. > There is no way you could do memory management of all but the most > trivial and fixed-length data chunks using a stack. Sure, you could > reserve thousands of bytes on the stack for an array but suppose your > language allows arrays to grow or shrink. To keep its property of > being adjacent, you'd have to do something horrible such as move > unrelated data allocated later, which raises all sorts of security > issues, doesn't it. > A stack, or something which works like a stack (that is, a stack) is a > necessary but not sufficient condition for a working C runtime because > C functions can call themselves recursively, whether directly or > indirectly. If this last condition did not obtain, each function could > give the functions it calls some of its own memory and the called > function could save a fixed set of non-stacked general registers in > that area; this was in fact the practice on IBM 370 and in assembler > language at a time when many "data processing managers" though > recursion was a Communist plot. > > However, data structures of variable size, or data structures that > merely take up a lot of space, don't play nice with others on the > stack, so, we place their address on the stack and store them in > another place, which was named the heap, probably, as a sort of > witticism. > > Gilbert and Sullivan: > > If anyone anything lacks > He'll find it all ready in stacks This you might want to take this to the Forth people because they are marketing their language as a cure for all that plagues programming today. > was wrong, and needs to be brought up to date: > > You cannot do everything in a stack > Unless you code an almighty hack > If you're a coding Knight who says, "Neep", > You'll probably need to implement a heap > A pile a heap of benefits you'll reap > If only my advice in your brain you'll keep > And avoid memory leaks from which data doth seep > By using a well-implemented, well structured, and well-documented > Heap! > > [Chorus of Sailors] > We will to heart your advice take, and always use a heap! > > [Soloist] > Oh thank you do > To this be true > And always my sage advice do keep > That you always need to use a heap!- Hide quoted text - > > - Show quoted text - -- http://mail.python.org/mailman/listinfo/python-list
