Good strategy for determining root set in C++

Just a very quick answer, Matthew ....

C++ would generally be called an "uncooperative" language for GC. The
compiler basically is not going to help you. Which means you have to code
it in somehow, assuming you want accurate root sets. If you are willing to
go for assuming that anything that looks like a root is a root, as in the
Boehm-Demers-Weiser method (often called the "Boehm collector"), then that
is a less intrusive technique, but restricts you to non-moving collection,
at least for objects referenced ambiguously from roots.

In theory one could hack the compiler to tell you more, but it would fail
for some programs, e.g., if they do their own address arithmetic or do
funky pointer encodings (rare, but possible).

Java systems (for example) generally build the support in (but gcj, built
basically as a front-end to gcc, uses the Boehm collector because the
compiler back-end does not do the work necessary to identify pointers
unambiguously).

Put another way, I consider it more a compiler issue than a language issue,
though both play a part, and the tradition has never built up for GC for C
and C++.

-- Eliot Moss
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