Smieciuch Garbage Collector

for C and C++

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Smieciuch is a precise (in case of C++) or nearly precise (in case of plain C) tracing garbage collector. Tracing means that GC scans memory for active pointers and traces all paths (consisting of possibly multiple pointer indirections) from so called memory roots (static global data and execution stack(s)) to any reachable allocated heap block. If there are not paths from memory roots into some block then such block is recognised as dead (unreachable) so it might be freed.
Being precise means that it is impossible to mess managed pointer (aka managed reference) with any other kind of program data. Oposite term is conservative - in such case collector (aka memory manager) does not know for sure if particular data is managed pointer or not and thus anything what might be pointer (that usually means anything whichs value might be interpreted as pointer into one of allocated heap areas) is treated as a live pointer to some memory area and thus protects that (allocated) area from being freed. So conservative garbage collector might (an in real life often does) recognise some dead memory objects as still alive (thus wasting memory).
In real life such problems get more and more pronounced when percentage of total address space used by application increases. And those are often the cases where memory usage is an important problem.
C++ Smieciuch is precise so there are no such issues, but more explanations are needed for C variant's near precission...
C Smieciuch is fully precise for everything but stack located managed references. If there is right (or rather wrong) set of conditions some non managed pointer data could for the eyes of collector impersonate some managed pointer used by some earlier invoked procedure. There must be three bads in line:

As one can see this problem is well localised. I'm thinking about techniques to reduce it even further, but I have no idea how to get rid of it completely.
Mind you, this is only the case of C code, as in C++ managed pointers are encapsulated by apropriate smart pointer classes and destructors take care of informing GC that particular managed pointer is no longer live.

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Smieciuch is © 2003 by InForma-Sebastian Kaliszewski, all rights reserved