Re: memory management and productivity

[David Starner <dvdeug@email.ro>]

On Wed, 23 Jun 2004 17:36:23 +0000, Bj�rn Persson wrote:

> Could someone enlighten me a little on the mysteries of garbage?
> 
> Since a garbage collector can apparently be compiled in as a library, 
> why isn't that good enough? Is it a great advantage to have it provided 
> by the compiler instead?

The only library garbage collectors I know about are conservative; they
assume that every pointer-size chunk of accessible memory is a pointer,
(unless it's in a block of data that was allocated with a special function
that tells the GC there are no pointers in that data.) They don't move
memory because you can't adjust pointers if you can't tell pointers from
integers. A garbage collector that was part of the compiler could tell
integers from pointers (that is, be a precise collector instead of a
conservative collector) and could move items in memory (which many
high-performance GCs do.) This makes easier, for example, for a compiler
to scan only the new stuff, which has a shorter live time than the stuff
the program has kept around for a while. The first may be more important;
a misplaced integer could potentially hold several megabytes of garbage in
memory.