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Re: shared libg2c?
On Tue, Oct 31, 2000 at 10:53:40PM +0100, Toon Moene wrote:
> nbecker@fred.net wrote:
>
> > >>>>> "Toon" == Toon Moene <toon@moene.indiv.nluug.nl> writes:
>
> > Toon> nbecker@fred.net wrote:
>
> > >> I suggest libgc2 be installed shared as well as archive, where
> > >> supported.
>
> > Toon> Note that for libg2c being installed shared *usefully* first of all the
> > Toon> code has to be made reentrant.
>
> > I don't understand. Could you please elaborate? Specifically, why is
> > it useful to have a non-reentrant archive lib, but it's not useful if
> > it's compiled as a shared lib?
>
> Because it is not useful to have a non-reentrant shared lib, period :-)
>
> The code (*all* code) in a shared library has to support multiple
> execution threads, because only one copy of the code is present,
> regardless of the number of "users" (i.e. callers of routines inside
> said shared library).
>
> To be reentrant, code has to follow a few guidelines, one of which is:
>
> *No static mutable variables, unless protected by a mutex*.
Don't modern dynamic linkers give each process its own copy of shared
libraries' global data? If it weren't so, classic errno (before
thread-safe libc) could never have worked - and I know there were
shared libcs before there were thread-safe libcs...
Multiple threads - sharing data as well as code - is another can of
worms, but f77 doesn't support threads anyway, last I checked.
zw