FreeTDS Development Group

["Craig A. Berry" <craigberry AT mac.com>]

On Oct 14, 2013, at 12:57 AM, Frediano Ziglio <freddy77 AT gmail.com> wrote:

> 2013/10/13 Craig A. Berry <craigberry AT mac.com>:
>> Make the VMS-specific configuration and build procedures handle threads, 
>> plus admit to having some other things that we do have but weren't 
>> configuring for, such as clock_gettime(), socketpair(), getaddrinfo(), and 
>> stdio locking.
>> 
>> The attached patch was created with git format-patch and should be 
>> applicable with git am.  Or GNU patch -p1 for traditionalists.
>> 
> 
> What can I say. Pushed!

Many thanks.

>> 6e3afa4d (Frediano Ziglio        2013-06-05 12:47:50 +0100 1127)        i 
>> = fgetc(hostfile);
>> 6e3afa4d (Frediano Ziglio        2013-06-05 12:47:50 +0100 1128)        if 
>> (i == EOF)
>> 6e3afa4d (Frediano Ziglio        2013-06-05 12:47:50 +0100 1129)           
>>      return _bcp_check_eof(dbproc, hostfile, 0);
>> 6e3afa4d (Frediano Ziglio        2013-06-05 12:47:50 +0100 1130)        
>> ungetc(i, hostfile);
>> 
> 
> Well... this patch use some stdio extension to make read faster... but
> fails on standard C calls ?? What a crazy world! It just try to detect
> if we are at end of the file without removing a character!


What you're doing is completely reasonable, but appears to trigger a pretty 
nasty bug in the C run-time where calling fgetc/ungetc corrupts the return 
value of a subsequent fread.  Since FreeTDS always checks the return value of 
fread in _bcp_read_hostfile, it knows something is bonkers and bails out.

I've documented what goes wrong with a simple reproducer at 
<https://sourceforge.net/p/vms-ports/tickets/72/>.  Not sure what to do yet 
as a workaround.  I guess we could skip the above if it's purely an 
optimization.  Or I could try to implement my own ungetc by fiddling with the 
pointers in the stdio struct.

________________________________________
Craig A. Berry
mailto:craigberry AT mac.com

"... getting out of a sonnet is much more
 difficult than getting in."
                 Brad Leithauser