On Jan 18, 2006, at 5:22 PM, Thomas Chust wrote:
actually I doubt that the termination of strings with a '\0'
character is broken. Maybe the problem is rather related to garbage
collection somehow, if the string is used for a longer time by the
readline library. But nevertheless your approach here looks sensible.
I previously had scheme_completion return a c-string, and I assumed
it would somehow generate a correctly null-terminated string. It did
in most cases, but occasionally there was a garbage character
afterward. If I did a (print) of the value I was about to return in
scheme_completion and a printf() in completion_func() right after it
was returned, I saw the garbage character appear between the two. I
don't think garbage collection could account for that.
How is returning a c-string from a define-external'd scheme function
supposed to work? Returning the scheme object worked fine in the
end, but it would have been a lot easier if there was some automatic
way.
So just replace the foreign-lambda* by foreign-safe-lambda* in your
readline.scm for every function that may eventually cause a
callback intro Scheme and everything should be fine.
This does appear to have fixed it! That's actually about the only
vestige of the original readline.egg that I still have in that file.
It worked there because there was no callback into scheme, and it
didn't even occur to me to check there. Thanks. :)
On Jan 18, 2006, at 7:11 PM, Zbigniew wrote:
It looks like Thomas is right about the callback, although I can't get
your example to crash. I'm running Mac OS X PPC, which sometimes
allows memory accesses that would cause segfaults elsewhere, so I have
another possibility if you still get crashes. Before testing for the
scheme string length in completion_func, you do a strcmp against "".
Here's the thing--scheme strings are never null terminated at all,
even when returned by C_c_string (which after all just returns a
pointer to the raw scheme data). In fact, a NULL string will be 0
bytes long. This strcmp will probably access the first byte of your
result string, which is an illegal memory access. Instead, you should
test that the scheme string size is 0 and return NULL if so.
I'm running Mac OS X PPC, too. My crasher program doesn't crash
nearly as quickly as my app does; if I hit <tab><tab><tab><return>
repeatedly it does eventually die, though. I think you're correct
about the strcmp, though, so I made that change as well. Thank you,
too!
It's a pleasure to get prompt and informed help from a first-time
post to a mailing list. Hopefully things will progress much more
smoothly now.
--Levi
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