[patch] Default to --enable-libstdcxx-time=auto

[Paolo Carlini]

On 05/22/2013 01:49 PM, Jonathan Wakely wrote:
> On 22 May 2013 12:15, Jakub Jelinek wrote:
>> If now() can be perhaps with worse precision emulated in configurations not
>> built against glibc 2.17, perhaps best solution would be to
>> add now()@@GLIBCXX_3.4.18 into 4.8.1 (and change all 3.4.18 symbols to
>> 3.4.19) and have now()@GLIBCXX_3.4.17 (note, just one @) as compatibility
>> alias to that.
> The problem for steady_clock::now() isn't one of precision, it's that
> it isn't steady if we don't use the monotonic clock.  We could define
> a non-steady steady_clock (with the same precision as system_clock)
> but is that helpful to users?  If that's what we want then yes, we can
> do the symbol versioning you suggest.
If I understand correctly Jakub's idea, nothing would change from the 
user point of view in the headers, using now would be still a no-no if 
the real facility isn't implemented. It would be only a run-time fall 
back for the situation I mentioned before: the binary is built with 
headers providing a good clock and then moved to another machine, and 
dynamically linked to a library which doesn't and then run. We could 
also spill a warning, at run-time.

That kind of solution would be definitely Ok with me.

Paolo.