Re: Ada 0Y plans for garbage collection?

["Robert I. Eachus" <rieachus@attbi.com>]

Ludovic Brenta wrote:

> Linus Torvalds differs quite strongly on this:
> 
> http://gcc.gnu.org/ml/gcc/2002-08/msg00571.html

Couldn't have said it better myself.  On one project I wanted to compare 
using garbage collection to Controlled types and managing the allocation 
and deallocation of objects myself.

First I wrote a version that just did heap allocation, with NO garbage 
collection.  Of course it was possible to run out of storage with this 
version, but I wanted to see how much overhead GC would add.  As long as 
I had a test case that did not result in paging, this was the ultimate 
best case for the GC version.

Then I changed the implementation to use a Controlled type, with 
explicit immediate frees as soon as an object was no longer used.  I 
added less than a page of code to implement all this.  Remember now the 
code is explicitly freeing everything.

The version with the Controlled type was three times as fast as the 
version with no deallocation.  You can imagine how motivated I was to 
find out how much overhead GC would add. ;-)  Worse, I then changed 
things a bit more.  Since all the nodes I was allocating were the same 
size, I grabbed a chunk of memory and used it as a reference counted 
heap where every object was the same size.  (I then twiddled a bit more 
so objects were exactly one cache line long, and my allocater returned 
blocks that were cache line aligned.)  Net result, this version was 
almost ten times as fast as the na�ve version that would quickly start 
paging to virtual memory if I let it.

-- 
                                               Robert I. Eachus

"As far as I'm concerned, war always means failure." -- Jacques Chirac, 
President of France
"As far as France is concerned, you're right." -- Rush Limbaugh