Re: libstdc++ and race detectors

[Paolo Carlini <paolo dot carlini at oracle dot com>]

Hi,
> Hi Paolo,
>
> On Fri, Jul 9, 2010 at 4:22 PM, Paolo Carlini <paolo.carlini@oracle.com> wrote:
>   
>> On 07/09/2010 01:29 PM, Kostya Serebryany wrote:
>>     
>>> Before we proceed with a bug report or a patch file, we'd like to know
>>> your opinion on the problem.
>>>
>>>       
>> I don't know if you are aware of that, but in the forthcoming, so-called
>> C++0x, standard reference counting implementations of basic_string will
>> be ruled out.
>>     
> Good!
> Will the library have any other code with atomic synchronization?
>   
Yes, just grep...
> I prepared a draft of this change: http://codereview.appspot.com/1800042 .
Please post any tentative change here, inline.
> Unfortunately, this change required to add  __attribute__
> ((always_inline)) to _M_dispose and ~basic_string. I am not sure this
> is acceptable.
> Without  __attribute__ ((always_inline))  the approach doesn't work
> because ~basic_string does not get inlined and we call the version of
> ~basic_string from libstdc++.so, which does not have the annotations.
> Any suggestion?
>   
This is not happening by chance: user code *is* supposed to use for
basic_string instantiated for char and wchar_t the symbols exported by
the .so. Essentially, for basic_string, you have to make up your mind at
library build time. The only exception we have is debug-mode, where the
trick is that -D_GLIBCXX_DEBUG essentially disables extern template (ie,
_GLIBCXX_EXTERN_TEMPLATE is -1 for debug-mode, see c++config). I would
suggest experimenting with that, as a last resort. Actually, I would
rather prefer trying to get in first a version of your change as clean
as possible, not using that trick, because we are already touching code
I would rather not touch at this stage, and anyway for other bits of the
library using reference counting and exported from the .so the trick is
not available anyway, because no templates are involved.

Paolo.