Re: [libstdc++] remove __compare_and_swap

[Phil Edwards <pedwards at disaster dot jaj dot com>]

On Fri, Oct 05, 2001 at 12:18:02PM -0700, Nathan Myers wrote:
> On Fri, Oct 05, 2001 at 02:45:08PM -0400, Phil Edwards wrote:
> > 
> > A couple weeks ago I proposed removing __compare_and_swap, an unused 
> > function from the CPU configuration headers that seems to confuse port
> > maintainers:
> > 
> >     http://gcc.gnu.org/ml/libstdc++/2001-09/msg00069.html
> 
> I apologize for not responding to the previous message.

Apology cheerfully accepted.

> Compare-and-swap is an essential primitive to maintain linked data 
> structures thread-safely without using an enormously more expensive,
> unportable, and otherwise problematical mutex.
> 
> We don't have much in the library yet for support of multithreaded
> programs, but eliminating primitives that such support would need 
> seems like the wrong direction to go.

. o O (Will we ever have that much support?)

Okay.  Given the confusion that __c_a_s has caused for port maintainers,
I suggest leaving it out until we actually try introducing MI support into
linked list structures.  It would be a pain to require new ports to submit
a function that may or may not need rewriting at some arbitrary future date.

Note that the recent CRIS port never had __c_a_s in the first place.  I,
personally, don't see the gain in putting the function back in if some
parts of config/cpu/ will still not have it.

After all, when MI support is actually added, we can always resurrect the
function, and /then/ ask the maintainers of CRIS and who knows what else
to implement it, when we can point to a place where it's actually being
used and tested.

Thoughts?


Phil

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