Re: [PATCH] Make the pointer parameter to __gthread_setspecific non-const

["Aaron W. LaFramboise" <aaronavay62 at aaronwl dot com>]

Richard Guenther wrote:
> On Sat, Aug 23, 2008 at 7:14 PM, Aaron W. LaFramboise
> <aaronavay62@aaronwl.com> wrote:
> > Currently on i386-pc-mingw32, casting away constness in
> > __gthread_setspecific causes a bootstrap failure with --enable-werror. This
> > must be true for a number of other targets which do the same thing.
> >
> > The ultimate problem here is that there's nothing about this parameter that
> > is const: __gthread_getspecific returns a non-const pointer, not a const
> > one.

> But pthread_setspecific _does_ take a constant pointer as argument.

Oh, how unfortunate.

I think this is a defect in POSIX pthreads.  This means if you pass in a 
const void * to pthread_setspecific, you can get a void * back out of 
pthread_getspecific, losing the constness without ever casting.

> Why not add an explicit cast for the mingw32 case?

An explicit cast does not kill the warning.  The union trick is the only 
way to get rid of it, and the encapsulation for this trick, CONST_CAST, 
is not available to gthr.h.

*-mingw* is not the only target with this issue.  Pretty much all 
non-pthreads targets have to cast away constness in the same way, since 
most other threading APIs apparently get this right.

So, is it better here to deviate slightly from pthreads, to do what 
seems more correct, or to use the union trick to make this warning go 
away in all pthreads targets?

I'm happy either way; someone just let me know what I should do.