[plt-scheme] sqlite.plt seg faults with 370

Is this truly a problem? I mean: sqld-psql.plt indead crashed
when used in multiple scheme threads, but they are in the
same OS thread. So...?

--Hans


Op 25/7/2007 schreef "Dave Gurnell" <d.j.gurnell at gmail.com>:

>The Untypers had problems with this a while back. This is my
>hypothesis as to what's going on (although it happened to us a year
>ago so I may be remembering things wrong):
>
>SQLite can be compiled in thread-safe and non-thread-safe modes
>(there's a switch on the compile or make step, I forget which). On
>Etch, the default package is non-thread-safe. The Scheme interface
>doesn't do anything to correct this, and concurrent queries can cause
>segfaults.
>
>You'll probably find that you get more crashes if you're doing lots
>of large queries, like selecting hundreds to thousands of rows as a
>time, because this increases the chance of multiple queries overlapping.
>
>So... you have options:
>
>   - fix things at the C level;
>   - fix things at the Scheme level (semaphores / channels / etc);
>   - compile your own version of SQLite with thread safety enabled.
>
>You could also try testing your code on OS X - it comes with a thread-
>safe copy SQLite pre-installed.
>
>Cheers,
>
>-- Dave
>
>>> I had the same problem with sqld-sqlite.plt. I fixed it, using
>>> semaphores. But now I got to think about it. SQLite uses callbacks
>>> from C to Scheme to return query results. Also it uses a callback
>>> function to fix locks. Maybe it has something to do with the moving
>>> GC (pointers get moved around)?
>>
>> The foreign implementation use immobile boxes to make sure that
>> pointers to Scheme callbacks don't change.  But you need to make sure
>> that they are not collected -- for example, avoid (lambda () ...) with
>> no additional references as callbacks.
>>
>> --
>>           ((lambda (x) (x x)) (lambda (x) (x x)))          Eli
>> Barzilay:
>>                   http://www.barzilay.org/                 Maze is
>> Life!
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