Re: Libification project (SoC)

[Johannes Schindelin <Johannes.Schindelin@gmx.de>]

Hi,

On Sun, 18 Mar 2007, Theodore Tso wrote:

> On Mon, Mar 19, 2007 at 02:43:54AM +0100, Johannes Schindelin wrote:
> > >   I was talking about the API. The API has to be designed to be 
> > > reentrant. And you get pretty much stuck with the API. And requiring 
> > > reentrance isn't that far off once libgit is there, as I tried to point 
> > > out; it's not really any obscure requirement.
> > 
> > - it is easy enough to extend the API later, _retaining_ the small and 
> >   beautiful functions.
> 
> Um, look at what we had to do with gethostbyname() and 
> gethostbyname_r().  It wasn't possible to sweep through and fix all of 
> the programs that used gethostbyname(), despite the fact that if a 
> program called gethostbyname(), then called library function which 
> unknowingly to application, could possibly do a DNS or YP lookup (and 
> whose behavior could change depending on some config file like 
> /etc/nsswitch.conf), which would blow away the static information.  So 
> if the application tryied to use the information returned by _its_ call 
> to gethostbyname after calling some other library function, it could get 
> some completely random hostname that wasn't what it expected.
> 
> Yelch!  And so we have two API's that libc has to support, 
> gethostbyname(), and gethostbyname_r(), with the ugly _r() suffix, and 
> which in a sane world most programs should use since otherwise they can 
> be incredibly fragile unless the _first_ thing they do after calling 
> gethostbyname is to copy the information to someplace stable, instead of 
> relying on the static buffer to remain sane.  (And yet they don't, which 
> means bugs that only show up if optional YP or Hesiod lookups are 
> enabled, etc.)
> 
> Berkely got it horribly wrong when it tried to start with the "small and 
> beautiful" functions that were non-reentrant, and we've been paying the 
> price ever since.  Do we really want to support two versions of the API 
> forever?  Is it really that hard to support a reentrant API from the 
> beginning?  I'd submit the answer to these two questions are no, and no, 
> respectively.

You make a good case why gethostbyname() was wrong, and should have been 
defined as gethostbyname_r() to begin with.

However, as I wrote in another reply in this thread, I am not prepared to 
sink more time in this discussion, _unless_ somebody who cares about it 
enough shows me some code and/or numbers.

Ciao,
Dscho