Hi,
1- Try to re-organize the new code in order to make possible using in
*few* selected places _GLIBCXX_ATOMIC_BUILTINS_4 to enable / disable
the new feature completely.
The necessary code changes for this are in the attached patch. Most of
the code doesn't need to be touched, because the added code doesn't
affect the non-exception_ptr case. The only thing that *needs* to
change is that the reference counting is removed from
__gxx_exception_cleanup. The reference count part of the
__cxa_exception struct can stay - it's simply unused, except for the
initialization in __cxa_throw.
Of course, that additional field and the initialization can be ifdefed
out too, if you want.
Ok, great, seems a sane approach to me. On the positive side, we should
also consider that each day more machines (certainly most the new ones
in the server / desktop / notebook classes) can use the new code.
The necessary configuration changes:
1) eh_ptr.cc must be excluded from compilation completely if the
feature is unavailable.
2) The test cases must be excluded from the test runs.
Ok, I'll do this, it's rather straightforward.
3) It needs to be remembered whether propagation was included in the
build. c++config needs to define _GLIBCXX_EXCEPTION_PTR_SUPPORTED on
platforms where it was. The issue here is that I don't know if
_GLIBCXX_ATOMIC_BUILTINS_4 keeps the value it had during the GCC build
when client programs get compiled, and the client would get weird
errors if it didn't. If it does, the new macro can simply be replaced.
Yes, no problem here too. In a first approximation, we can also avoid
_GLIBCXX_EXCEPTION_PTR_SUPPORTED and just rely on
_GLIBCXX_ATOMIC_BUILTINS_4. But if people would find that useful, we can
at some point add code to acinclude.m4 to define at configure time
_GLIBCXX_EXCEPTION_PTR_SUPPORTED consistently with the outcome for
_GLIBCXX_ATOMIC_BUILTINS_4. Actually that strategy, defining at
configure time fine-grained macros, one for each enabled / disabled
C++0x feature which requires some sort of support not always available,
seems a nice one in general, let's revisit the library about that in a
few weeks, when we'll be feature complete for 4.4.0.
Paolo.
