[CM] S7s GC

[bil at ccrma.Stanford.EDU]

in C:

s7_gc_on(sc, false); /* blocks the GC from running, but the heap will 
grow if necessary */
s7_gc_on(sc, true).  /* allow the GC to run, does not trigger the GC */

in Scheme:
(gc #f) ; same as s7_gc_on(sc, false)
(gc #t) ; turns GC on and calls the GC

I could change (gc #t) to simply re-allow GC's I suppose.

On the times: here I am running s7test (which creates lots of objects) 
with
(set! (*s7* 'gc-stats) #t)

/home/bil/motif-snd/ repl s7test.scm
load s7test.scm
gc freed 111174/128000 (free: 126037), time: 0.000683
gc freed 117417/128000 (free: 125595), time: 0.000442
gc freed 111427/128000 (free: 111491), time: 0.000632
gc freed 109546/128000 (free: 111432), time: 0.000835
gc freed 103932/128000 (free: 111446), time: 0.000549
gc freed 123825/128000 (free: 125522), time: 0.000489
gc freed 95883/128000 (free: 123736), time: 0.000485
gc freed 3015/128000 (free: 123799), time: 0.000366
gc freed 121331/128000 (free: 121395), time: 0.000806
gc freed 123449/128000 (free: 123513), time: 0.000741
gc freed 107711/128000 (free: 123489), time: 0.000832
gc freed 111976/128000 (free: 123443), time: 0.000642
gc freed 109104/128000 (free: 115881), time: 0.000687
gc freed 101924/128000 (free: 115603), time: 0.000579
gc freed 98488/128000 (free: 114473), time: 0.000575
...

So the interruption is normally less than a millisecond (this is using
the default heap-size, but I don't think that matters much).  The mark
process is almost insignificant in the overall computation, so don't 
worry
about object types or layouts. The only case I've seen where it matters
are GC benchmarks based on millions of huge lists (mark_pair traverses
each list, which can become tedious).

It's possible you haven't noticed the GC because it's not being
called much -- s7 goes to great lengths to avoid creating
objects itself:

(define (f)
   (do ((i 0 (+ i 1))
        (sum 0))
       ((= i 1000) sum)
     (set! sum (+ sum i))))

(gc)
(set! (*s7* 'gc-stats) 7)
(display (f)) (newline)
(gc)
;; gc freed 102/128000 (free: 127828), time: 0.000084

Set gc-stats and run your code -- maybe you don't need to do anything.

I think if you have 2 threads calling into the same s7 interpreter, you 
do need
to be sure they don't interrupt each other.  If you try to call 
s7_eval_c_string
or something while the GC is being run from some other thread, you'll be 
unhappy.