Re: Re[6]: [Haskell-cafe] Boxed Mutable Arrays

brad.larsen:

On Tue, Dec 15, 2009 at 11:33 AM, Serguey Zefirov wrote:

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If the number of buckets was fixed, one could use an array of STRefs to lists.  I believe this would avoid the bug from Ticket #650? now i see what you mean. no, i mean trivial transformation. #650 says about slow GC. why it's slow? because once you made any update to the array, the entire array is marked as updated and scanned on next minor GC (which occurs after every 512 kbytes allocated, afaik). let's replace big array (say, of 10,000 elements) with array of 100 arrays of 100 elements each. now, between minor GCs only some of arrays will be changed and entire amount of memory to be scanned will become less

Data.IntMap?

I want to implement a more-or-less traditional, mutable, imperative hash table in the ST monad. Hence, I'm not considering Data.IntMap and other persistent tree structures for its implementation, although I have thought about it.

The bug described in Ticket #650, AFAICS, prevents implementation of a reasonable, generic hash table in Haskell. :-(

You can certainly implement it, it just requires that you increase the heap size to a bit bigger than your hash to reduce the pressure on the GC. But note, Simon's making progress, http://hackage.haskell.org/trac/ghc/ticket/650#comment:17 -- Don