Re: __libc_single_threaded design

[Florian Weimer <fweimer at redhat dot com>]

* Siddhesh Poyarekar:

> On 07/10/19 1:54 pm, Florian Weimer wrote:
>> Okay, let's change the subject of this subthread.
>> 
>> We need a name in the reserved space because the variable will be used
>> from libstdc++.
>
> My understanding of the __libc (or __cxa on the other end) namespace is
> that you'd want it if libstdc++ (and standard libraries, including glibc
> itself) are the *only* intended users.  For a proper public symbol (i.e.
> something we declare as widely available) it seems better to me to have
> a name without the __libc prefix.

We can make pthread_single_threaded_np.  That variable libstdc++ might
even want to use directly, without a __ prefix.

I do not feel *very* strongly about this.  But adding a second variable
due to aesthetic considerations, possibly introducing bugs as a result,
is not something what I like.

We had this discussion several years ago about __secure_getenv.  Oh
well.

>> The name is easy to change.  I believe we have support in the link
>> editor so that linking to the public name also links against the private
>> name.  If everything else fails, we could also have two variables which
>> are updated at the same time.
>
> Making a strong alias should be sufficient, but would we ever come
> across a situation where the public and __libc_* name may assume
> different meanings and hence need to exist as different variable names?

Hmm.  We are in this situation with some of the math functions and
signgam.  But I think there it works because nothing in the library
calls gamma and lgamma spontaneously.  pthread_single_threaded_np would
be different because pthread_create in strict POSIX mode would still
assign to it.

Thanks,
Florian