From: Jeannot_Langlois <address@hidden>
Reply-To: address@hidden
To: Raji Easwaran <address@hidden>
CC: address@hidden, address@hidden
Subject: Re: Threadsafe C Based Parser
Date: Fri, 03 Sep 2004 15:02:07 -0400
[CC'ing the Flex and Bison mailing lists, as this should be of common
interest to both...]
Hi Raji,
Effectively, it seems that we encountered the same problems with Flex and
Bison.
Raji Easwaran wrote:
Jeannot,
We are in the process of making one of our parsers threadsafe. We
currently use Bison version 1.75 and Flex version 2.5.4. We are
considering using the %pure_parser option on bison to make the parser
thread safe and were looking into using %option reentrant option in Flex
to make the scanner threadsafe. I was looking at [
http://lists.gnu.org/archive/html/bug-bison/2003-03/msg00031.html] and
noticed that you had the same requirements as me.
We want to use a C based parser and scanner. We have been trying to get a
version of flex that will support the reentrant option but have not had
much luck. Can you point me to where I can get a thread safe scanner? You
mentioned that you used version 2.5.27 of the scanner. Do you have a link
to where I can download this version?
When I was fiddling to get reentrant-Flex and reentrant-Bison to interact
properly in 2003, I found out that newer versions of Flex were being
released on SourceForge (I guess I was lucky with either a Google or
Freshmeat search...). At the time I wrote the message you quoted, Flex
2.5.27 was the latest version available at sourceforge. Today I see that a
newer version of Flex, 2.5.31, seems to have been released. I haven't tried
anything with this newer version, tough, but I guess it should fix a few
things which *might* help you out.
I found out the newer Flex site to be at:
http://lex.sourceforge.net
Here's the link to the downloads sections of Flex on sourceforge:
http://sourceforge.net/project/showfiles.php?group_id=72099
Also which option did you use to generate the reentrant scanner? Did you
use %option reentrant or %option reentrant-bison? Flex 2.5.4 does not seem
to recognize either of these options. If you think there are more recent
versions of Flex or Bison that we can use, please let me know.
Thanks in advance for your help. Any help regarding this will be much
appreciated.
Raji
I believe links I've given you above should help you out a little bit.
Looking through my old files I found out that I was using the following
options in my Makefile:
__________________________________________________________________________________________________
flex -R --bison-bridge -s -B -Cemr -L -v -p -i --header-file=myscanner.h
-omyscanner.c myscanner.lex
__________________________________________________________________________________________________
I also had the following options set in "myscanner.lex":
_________________________________________________
%option reentrant
%option header-file="myscanner.h"
_________________________________________________
I remember fiddling with "%reentrant" and "%reentrant-bison" options, but
can't remember the difference between the two and why I choose one over the
other -- I've been doing so much things since that time... eheh :-). Maybe
this is related with that "--bison-bridge" option I had used. I guess a
bit of reading and documentation will be required here from the reader :-).
I couldn't get completely satisfied with Flex for what I needed to do
because it caused me some troubles when interfacing with Bison (reentrency,
custom parameter passing, etc...).
Maybe these issues have been resolved now -- I don't know, because after
some headaches back then, I decided to write my own reentrant C lexical
scanner by hand to interact with Bison (and am now using the newer
"%parse-param" and "%lex-param" Bison directives -- which are really nice
ways to pass custom parameters to yyparse() and then to yylex() in Bison--,
POSIX RegExp libraries, etc...), so I kinda got rid of Flex :-). I use my
own lexical scanner with Bison, not Flex and Bison as you as currently
trying to do.
But maybe with a little more patience than me and the newer Flex/Bison
versions you should be able to get reentrant-Flex and reentrant-Bison to
interact properly together.
As a little side-note, even if Bison 1.875 is the latest stable version, I
had some discussions with Paul Eggert (from the Bison team), and a feature
which I required (%destructor directive) was still unstable in Bison 1.875
and was producing Segmentation faults on compilation, so I installed a
newer "beta" Bison version: 1.875c -- it runs fine and seems quite stable
*to me*. Just in case you could be using that Bison feature too :-).
So, hopefully these notes should help you out... and maybe a couple of
other people too!
"We now return to our regular programming...".
Good luck,
--
Jeannot Langlois
B. Sc. Computer Science / B. Sc. Informatique
jeannot12 AT linuxmail DOT org
icq : 1-5-2-6-2-8-9-1
msn : jeannot12 AT hotmail DOT com
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