Should __clockid_t be used instead of clockid_t in pthread.h?

[Raphael Kubo da Costa-2]

Hi there.

I'm trying to build an unstable glib version here, and one of their
tests fails to build due to them #defining _POSIX_C_SOURCE to 0 and
then #including <pthread.h>, which produces the following error on my
8-STABLE machine:

/usr/include/pthread.h:184: error: expected declaration specifiers or '...' before 'clockid_t'
/usr/include/pthread.h:187: error: expected declaration specifiers or '...' before 'clockid_t'
/usr/include/pthread.h:203: error: expected declaration specifiers or '...' before 'clockid_t'

pthread.h gets its definition of clockid_t from time.h, but time.h only
creates the typedef if __POSIX_VISIBLE is >= 199309. Using __clockid_t
instead of clockid_t in the function prototypes works fine.

Should the prototypes be changed?

Thanks.

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[Bruce Evans-4]

On Sun, 18 Mar 2012, Raphael Kubo da Costa wrote:

> Hi there.
>
> I'm trying to build an unstable glib version here, and one of their
> tests fails to build due to them #defining _POSIX_C_SOURCE to 0 and
> then #including <pthread.h>, which produces the following error on my
> 8-STABLE machine:

This gives undefined behaviour.

> /usr/include/pthread.h:184: error: expected declaration specifiers or '...' before 'clockid_t'
> /usr/include/pthread.h:187: error: expected declaration specifiers or '...' before 'clockid_t'
> /usr/include/pthread.h:203: error: expected declaration specifiers or '...' before 'clockid_t'
>
> pthread.h gets its definition of clockid_t from time.h, but time.h only
> creates the typedef if __POSIX_VISIBLE is >= 199309. Using __clockid_t
> instead of clockid_t in the function prototypes works fine.
>
> Should the prototypes be changed?

time.h is a standard C header, so not defining clockid_t in it when POSIX
extensions are disabled is correct.

pthread.h is a not-so-old POSIX header, so it can assume that
__POSIX_VISIBLE is >= 199309.  Including it when POSIX is not visible,
or when only an older version of POSIX is visible, is just nonsense
and can have any result, like the one here.  While using __clockid_t
in in might make it sort of work, it would remain quite broken.  POSIX
requires that pthread.h shall make all the namespace pollution in
time.h (and some other headers) visible.  This is a bug in POSIX.  It
actually requires that pthread.h shall make all the [POSIX] symbols
in time.h visible.  pthread.h just includes time.h to get all of these
symbols, and becomes broken if ones like clockid_t are not declared.
If pthread.h is actually used, then programs using it will actually
need some of the symbols like clockid_t from time.h and break when
they don't explicitly include time.h.

Bruce
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[Raphael Kubo da Costa-2]

Bruce Evans <[hidden email]> writes:

> On Sun, 18 Mar 2012, Raphael Kubo da Costa wrote:
>
>> Hi there.
>>
>> I'm trying to build an unstable glib version here, and one of their
>> tests fails to build due to them #defining _POSIX_C_SOURCE to 0 and
>> then #including <pthread.h>, which produces the following error on my
>> 8-STABLE machine:
>
> This gives undefined behaviour.
>
>> /usr/include/pthread.h:184: error: expected declaration specifiers or '...' before 'clockid_t'
>> /usr/include/pthread.h:187: error: expected declaration specifiers or '...' before 'clockid_t'
>> /usr/include/pthread.h:203: error: expected declaration specifiers or '...' before 'clockid_t'
>>
>> pthread.h gets its definition of clockid_t from time.h, but time.h only
>> creates the typedef if __POSIX_VISIBLE is >= 199309. Using __clockid_t
>> instead of clockid_t in the function prototypes works fine.
>>
>> Should the prototypes be changed?
>
> time.h is a standard C header, so not defining clockid_t in it when POSIX
> extensions are disabled is correct.
>
> pthread.h is a not-so-old POSIX header, so it can assume that
> __POSIX_VISIBLE is >= 199309.  Including it when POSIX is not visible,
> or when only an older version of POSIX is visible, is just nonsense
> and can have any result, like the one here.  While using __clockid_t
> in in might make it sort of work, it would remain quite broken.  POSIX
> requires that pthread.h shall make all the namespace pollution in
> time.h (and some other headers) visible.  This is a bug in POSIX.  It
> actually requires that pthread.h shall make all the [POSIX] symbols
> in time.h visible.  pthread.h just includes time.h to get all of these
> symbols, and becomes broken if ones like clockid_t are not declared.
> If pthread.h is actually used, then programs using it will actually
> need some of the symbols like clockid_t from time.h and break when
> they don't explicitly include time.h.

Thank you for the detailed explanation. I've filed a bug in glib's
Bugzilla [1] with a proposed fix that should work on both FreeBSD and
Linux.

[1] https://bugzilla.gnome.org/show_bug.cgi?id=672406
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[Garrett Wollman-2]

<<On Mon, 19 Mar 2012 14:34:51 -0300, Raphael Kubo da Costa <[hidden email]> said:

> Thank you for the detailed explanation. I've filed a bug in glib's
> Bugzilla [1] with a proposed fix that should work on both FreeBSD and
> Linux.

Unfortunately, your proposed fix has the result of requesting a
*strict* POSIX environment, so applications that depend on system
interfaces that were not in the 1993 threading amendments will no
longer compile.  Maybe this doesn't matter in the specific case of
your testing framework, but it's not a universally correct solution.

-GAWollman

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