Re: [PATCH v6 1/4] git: make super-prefix option

[Jeff King <peff@peff.net>]

On Tue, Oct 04, 2016 at 10:31:51AM -0700, Stefan Beller wrote:

> On Thu, Sep 29, 2016 at 2:48 PM, Brandon Williams <bmwill@google.com> wrote:
> 
> >
> > +const char *get_super_prefix(void)
> > +{
> > +       if (!super_prefix)
> > +               super_prefix = getenv(GIT_SUPER_PREFIX_ENVIRONMENT);
> > +       return super_prefix;
> > +}
> > +
> 
> As said earlier, is the following a valid thought:
> 
> > The getenv() function returns a pointer to the value in the
> > environment, or NULL if there is no match.
> > So in case this is not set (when e.g. the user did not specify the
> > super prefix), we would probe it a couple of times.
> > The caching effect only occurs when the string is set. So this looks
> > like we save repetitive calls, but we do not always do that.

I think your concern is valid. If it is not set, we will do an O(n)
search through the whole environment on each call.

I also think the result of getenv() needs to be copied. In some
implementations it persists for the life of the program, but that's not
guaranteed; it may be overwritten by unrelated calls to getenv() or
setenv().

-Peff