From: Szabolcs Nagy <szabolcs.nagy@arm.com>
To: Florian Weimer <fweimer@redhat.com>
Cc: libc-alpha@sourceware.org
Subject: Re: [PATCH 1/2] Add the __libc_single_threaded variable
Date: Thu, 21 May 2020 14:26:41 +0100 [thread overview]
Message-ID: <20200521132641.GG14130@arm.com> (raw)
In-Reply-To: <87sgft77i0.fsf@oldenburg2.str.redhat.com>
The 05/21/2020 15:16, Florian Weimer wrote:
> * Szabolcs Nagy:
> > The 05/20/2020 20:12, Florian Weimer via Libc-alpha wrote:
> >> The variable is placed in libc.so, and it can be true only in
> >> an outer libc, not libcs loaded via dlmopen or static dlopen.
> >> Since thread creation from inner namespaces does not work,
> >> pthread_create can update __libc_single_threaded directly.
> >>
> >> Using __libc_early_init and its initial flag, implementation of this
> >> variable is very straightforward. A future version may reset the flag
> >> during fork (but not in an inner namespace), or after joining all
> >> threads except one.
> >> ---
> > ...
> >> +* The GNU C Library now provides the header file <sys/single_threaded.h>
> >> + which declares the variable __libc_single_threaded. Applications are
> >> + encouraged to use this variable for single-thread optimizations,
> >> + instead of weak references to symbols historically defined in
> >> + libpthread.
> >
> > i wonder if the new header can be included into
> > threads.h and pthread.h, and a feature macro added
> > for it, so users can avoid doing a header check.
>
> Isn't __has_include in current compilers sufficient for that?
>
> The advantage of the current approach is that libstdc++ headers can use
> __has_include on the new headers, without pulling in other headers which
> declare identifiers which are not in implementation namespace and also
> not expected to be used by C++ standard headers.
ok i guess __has_include is fine (assuming the macro expansion
bugs are fixed)
next prev parent reply other threads:[~2020-05-21 13:26 UTC|newest]
Thread overview: 45+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-20 18:12 [PATCH 0/2] Add __libc_single_threaded Florian Weimer
2020-05-20 18:12 ` [PATCH 1/2] Add the __libc_single_threaded variable Florian Weimer
2020-05-21 13:07 ` Szabolcs Nagy
2020-05-21 13:16 ` Florian Weimer
2020-05-21 13:26 ` Szabolcs Nagy [this message]
2020-05-20 18:12 ` [PATCH 2/2] manual: Document __libc_single_threaded Florian Weimer
2020-05-21 7:52 ` Michael Kerrisk (man-pages)
2020-05-21 12:17 ` Florian Weimer
2020-05-21 11:18 ` Szabolcs Nagy
2020-05-21 12:16 ` Florian Weimer
2020-05-21 12:50 ` Adhemerval Zanella
2020-05-21 13:09 ` Szabolcs Nagy
2020-05-21 13:15 ` Adhemerval Zanella
2020-05-21 13:30 ` Szabolcs Nagy
2020-05-21 13:44 ` Florian Weimer
2020-05-21 13:58 ` Adhemerval Zanella
2020-05-21 14:03 ` Florian Weimer
2020-05-22 10:01 ` Szabolcs Nagy
2020-05-22 10:05 ` Florian Weimer
2020-05-22 10:54 ` Szabolcs Nagy
2020-05-22 11:08 ` Florian Weimer
2020-05-22 15:07 ` Rich Felker
2020-05-22 16:14 ` Rich Felker
2020-05-22 16:36 ` Adhemerval Zanella
2020-05-22 17:02 ` Florian Weimer
2020-05-22 17:18 ` Florian Weimer
2020-05-22 17:28 ` Rich Felker
2020-05-22 17:40 ` Florian Weimer
2020-05-22 17:49 ` Rich Felker
2020-05-22 19:22 ` Szabolcs Nagy
2020-05-22 19:53 ` Rich Felker
2020-05-23 6:49 ` Szabolcs Nagy
2020-05-23 16:02 ` Rich Felker
2020-05-25 8:08 ` Florian Weimer
2020-05-25 8:08 ` Florian Weimer
2020-05-25 17:21 ` Rich Felker
2020-05-27 11:54 ` Florian Weimer
2020-05-27 15:36 ` Rich Felker
2020-06-03 15:00 ` Florian Weimer
2020-06-03 17:11 ` Rich Felker
2020-05-21 13:56 ` Adhemerval Zanella
2020-05-21 13:14 ` Florian Weimer
2020-05-21 14:32 ` Adhemerval Zanella
2020-06-03 15:48 ` Florian Weimer
2020-06-03 17:52 ` Adhemerval Zanella
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