[plt-scheme] Re: sxml package runs away on load, but only in mzscheme

From: John Clements (clements at brinckerhoff.org)
Date: Fri Jan 25 15:07:42 EST 2008

On Jan 24, 2008, at 2:44 AM, Dmitry Lizorkin wrote:

>> I'm observing something strange about the new sxml/ssax packages;  
>> requiring the package in mzscheme hangs and consumes all CPU, ..
> Indeed!
> It seems that mzscheme v 399 hangs on the phase of compiling zos for  
> the package sources. The problem can also be reproduced by running  
> setup-plt -l for the package.
>> Also, the first download from the  planet repository also hangs.
> IIUC, mzscheme attempts to create zo files on the first download  
> from the planet repository; subsequent 'require's from planet work  
> fine.
> Sorry for missing this. Before submission, I successfully unit  
> tested the package code for both PLT v 360 and v 399 and  
> successfully compiled the package sources into zo files for PLT v  
> 360, but not v 399. OTOOH, I believe that a package submitter alone  
> should not be able to hang the compiler; the package itself had no  
> drastic code changes since as long as PLT v 20X. I thus believe that  
> someone from PLT developerment team could elaborate the question  
> better than me.

This was bothering me again today, so I spent some time trying to  
narrow it down.  It appears that the problem occurs at least once in  
the "lazy-xpath.ss" module.  In particular, requiring this module hangs:

computer:~/Library/PLT Scheme/planet/300/ 
sxml.plt/2/0 clements$ mzscheme
Welcome to MzScheme v3.99.0.9 [3m], Copyright (c) 2004-2008 PLT Scheme  
 > (require "lazy-xpath.ss")
^Cuser break

... and commenting out everything but the "requires" allows it to run  
fine.  In fact, clicking "check syntax" while this file is open in a  
drscheme buffer causes DrScheme to run away.

I'm not familiar enough with this module to immediately spot the  
likely culprits; maybe you are?

John Clements

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