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Cc: OCaml List <caml-list@yquem.inria.fr>
Message-Id: <55B43ABC-5EC3-4277-BFED-7151AA05B972@cs.berkeley.edu>
From: Brighten Godfrey <pbg@cs.berkeley.edu>
To: Markus Mottl <markus.mottl@gmail.com>
In-Reply-To: <f8560b80904291238v4a202e23gfda4e4ff0807bc0@mail.gmail.com>
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Subject: Re: [Caml-list] Strange performance bug
Date: Wed, 29 Apr 2009 13:23:34 -0700
References: <324B24CA-9671-42C0-B722-C7710C0C45C7@cs.berkeley.edu> <59BD1B3A-B449-4963-9910-ED5E755D00E6@cs.berkeley.edu> <49F7F135.5080504@gmail.com> <08C6A0FC-90F2-43A4-AB78-4A3B68291FAA@cs.berkeley.edu> <49F7F59B.7070204@frisch.fr> <6D9C5A68-1874-4BBC-AE3D-9CCC3614AF7C@cs.berkeley.edu> <f8560b80904290658p6f5cacb9vb6a2cec1c77359a4@mail.gmail.com> <0FDD87FB-2461-4BBC-BDB1-5316A5AE4D23@inria.fr> <f8560b80904290903sdfb97fdr785def77f1c82712@mail.gmail.com> <25CD1992-3F33-4AEA-97A3-EC54729EC4FE@cs.berkeley.edu> <f8560b80904291238v4a202e23gfda4e4ff0807bc0@mail.gmail.com>
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X-Spam: no; 0.00; bug:01 markus:01 mottl:01 pcre:01 ocaml-values:01 pcre:01 regexps:01 deallocated:01 finalizer:01 ocaml-value:01 ocaml-heap:01 pcre-library:01 ocaml-heap:01 2009:98 eating:98 

On Apr 29, 2009, at 12:38 PM, Markus Mottl wrote:

> On Wed, Apr 29, 2009 at 15:19, Brighten Godfrey  
> <pbg@cs.berkeley.edu> wrote:
>> You seem to have solved my problem.  But out of curiosity:  Do you  
>> know how
>> the GC settings in the Str library differ from PCRE's, and why?   
>> Why does
>> PCRE need to explicitly trigger GCs at all?
>
> Str regular expressions are pure OCaml-values, whereas PCRE regexps
> are allocated on the C-heap.  Since C-heap values need to be
> deallocated explicitly, a finalizer has to be installed that does the
> job if the OCaml-value is not reachable anymore.  The OCaml-runtime
> needs hints about how large these C-values are.  Otherwise it may not
> scan the OCaml-heap aggressively enough, leaving a lot of those
> C-values floating around and eating up your memory.
>
> Right now the PCRE-library guarantees that not more than 500 regular
> expressions will float around at any one time.  This can lead to
> considerable slowdowns if your OCaml-heap is large and you allocate
> regular expressions at very high rates.

Got it.  Thank you all for your replies!

~Brighten