[Help-smalltalk] Re: the garbage collector is not doing its job

[Paolo Bonzini]

On 01/21/2009 07:20 AM, Derek Zhou wrote:
> On Monday 19 January 2009 12:34:02 am you wrote:
> > I actually applied this patch instead, but you must be thanked anyway
> > for the debugging.
> Another thing is I don't think the _gst_incremental_gc_step function in
> oop.c is doing what it means to do:
> void
> _gst_incremental_gc_step ()
> {
>    OOP oop, firstOOP;
>    int i;
>
>    for (i = 0, oop = _gst_mem.highest_swept_oop,
>         firstOOP = _gst_mem.last_swept_oop;
>         i<= INCREMENTAL_SWEEP_STEP&&  --oop>  firstOOP;
>         oop->flags&= ~F_REACHABLE)
>      {
>        if (--oop>  firstOOP)
>          {
>            finished_incremental_gc ();
>            break;
>          }
>
>        if (!IS_OOP_VALID_GC (oop))
> ...
> If you look closely there is no practical way it can get to the
> IS_OOP_VALID_GC check, let alone the actual sweeping. However my attempt
> of fixing it intuitively caused gst to crash so I don't know...

I think I fixed it now. :-)  Just because after six months I had a good 
reason. :-)

The bug was just that _gst_mem.last_swept_oop was totally wrong and 
basically worked by chance.  Yes, I mean it...

The reason I went back to it, is that I wanted to remove the usleep (1) 
almost-busy wait (poll every millisecond) for signals done in 
VMpr_Processor_yield.  The changes would be as follows:

1) when GST is idle, it tries doing an incremental garbage collection 
step, fifty times per second

2) in addition, if there are any, it runs the idle blocks 
(ProcessorScheduler>>#idleAdd:) round-robin, also fifty times per second.

3) if there is no idle block and the GC is done, however, it can just 
sigsuspend until the next signal.

I had this ready a while ago except that because of the above bug, it 
would never finish the incremental GC, and never go sigsuspend. :-(

I'll push after some more testing on Swazoo.

Paolo