From: Florian Gilcher <flo@...>
Date: 2009-11-10T11:32:06+09:00
Subject: Re: Good or best way to allocate a large array

Hi,

You can manually kickstart the GC by using GC.start.

   http://ruby-doc.org/core/classes/GC.html#M003682

Otherwise, AFAIK, the MRI GCs before breaking certain memory barriers,  
but
don't quote me on that. (I think it does that by counting mallocs and
starting the GC once a certain number is hit)

This actually explains this behavior:

   $ time ruby19 -e 'x=1<<63;Array.new(300_000*20) {1<<63}'
   real	  0m4.091s
   user	  0m3.430s
   sys	  0m0.361s

   $ time ruby19 -e 'GC.disable; x=1<<63;Array.new(300_000*20) {1<<63}'

   real	  0m2.489s
   user	  0m1.845s
   sys	  0m0.565s

But be aware though, that this is not caused by the allocation
of the array:

   $ time ruby19 -e 'x=1<<63;Array.new(300_000*20) {x}'

   real	  0m0.846s
   user	  0m0.735s
   sys	  0m0.049s

   $ time ruby19 -e 'GC.disable; x=1<<63;Array.new(300_000*20) {x}'

   real	  0m0.778s
   user	  0m0.710s
   sys	  0m0.052s


So, before (knowingly) breaking those limits, it might be an option
to disable the GC. Handle with care, though.

Regards,
Florian

On Nov 9, 2009, at 9:05 PM, Ralph Shnelvar wrote:

> Rick,
>
> Ok ... but the point is that the objects are not gc'd when things go
> out of scope but, instead, when Ruby needs memory, right?
>
> And if you have a huge array with gobs of objects, the gc is gonna
> take a while?
>
> Ralph