FreeTDS Development Group

["Lowden, James K" <LowdenJK AT bernstein.com>]

> From: Brian Bruns [mailto:camber AT ais.org]
> Sent: August 29, 2002 12:42 PM
>
> can someone give me a quick summary on this?  

OK, but quick isn't my forte. :)

> I'd rather not have any thread primitives in the
> library if we can avoid it even if it does mean implementing 
> our own on
> those platforms that don't have a suitable reentrant function. 

No one's added any threading code per se that I know of.  

> And if we
> have suitable functions on different platforms (Tru64 has X, 
> linux has Y, HP/UX has Z) can we wrap them and use autoconf to test?

That's what we do.

Basically, there was one call to vsnprintf(); it supported dbfcmd().  Nick
looked at it, decided what was really needed was vasprintf().  He sent it in
as PD.  I added it, wrapping the body of the .c in #if !HAVE_VASPRINTF, so
the module is effectively empty if the OS provides an implementation.  

Nick's implementation relied on writing to a too-small buffer, trapping
SIGSEGV, extending the buffer as needed.  Works single threaded, very nice,
a joy to behold.  Multithreaded, though, could cause a problem because of a
race condition:

1.      enter vasprintf.
2.      install signal handler, prepare to write to buffer.
3.      other thread faults.
4.      vasprintf handler does something stupid.
5.      bad things happen. 

Nick's long mail details why there's no good way for a library to deal with
signal handling in threaded environments.  So goes the war.  He is
re-implementing the function such that it doesn't rely on signals.  

--jkl


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