[gclist] Purify Find new leaks performance / Real GC performance

[Nick Kramer]

Excerpts by ianr@lsl.co.uk 
> The only time I have used a GC on our C code, is Purify (A C checking 
> tool, that find leaks).  Does anyone have some idea how its speed
> compares to the speed of a conservative GC?

Purify is not a garbage collector.  It "solves" the problem of memory
leaks by pointing leaks out to you, which you in turn fix.  A real GC
solves memory leaks by automatically deallocating memory for you when
there's no more pointers to the memory in question.

Last time I used Purify, it slowed my program down by at least an order
of magnitude.  A program with a real garbage collector generally runs at
about the same speed as the same program using free(), say, within 20%
either way. Much of the traffic on this list has been in trying to
narrow down that +/-20% estimate; another favorite topic is discussing
the (somewhat pathalogical) cases in which GC truly hoses performance.


-Nick Kramer