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Date: Mon, 08 Dec 2014 22:11:49 +0100
From: Jörg Krause <jkrause@...teo.de>
To: musl@...ts.openwall.com
Subject: Re: pthread_equal
On Mo, 2014-12-08 at 11:25 -0500, Rich Felker wrote:
> On Mon, Dec 08, 2014 at 05:18:41PM +0100, Jörg Krause wrote:
> > On Mo, 2014-12-08 at 09:56 -0500, Rich Felker wrote:
> > > On Mon, Dec 08, 2014 at 03:42:25PM +0100, Jörg Krause wrote:
> > > > Why does musl declares pthread_equal both as macro and as function?
> > >
> > > C and POSIX allow any of their standard functions to be provided as
> > > macros too, but the function definition must always be provided. The
> > > reason I put the macro in musl is simply that it's easy to do and
> > > gives better code (trivial inline comparison rather than spilling all
> > > registers and making a function call) and it's not something where the
> > > implementation could change or need to change.
> >
> > I see! The problem was, that MPD (Music Player Daemon, implemented in C
> > ++) for instance used ::pthread_equal(id, other_id) which did not build
> > with musl because of the macro expansion.
> >
> > The maintainer removed the namespace operator to get it work with musl:
> > http://git.musicpd.org/cgit/master/mpd.git/commit/?h=v0.18.x&id=d8fc2db910a11dbbba53ba7ecf96d0e32a081076
>
> I see.
>
> For the standard C headers, the C++ versions are supposed to omit the
> macros that the C versions might offer. However, there's no such rule
> for POSIX headers since there's no formal spec for interaction of C++
> and POSIX at all. Perhaps it would be useful to take the same approach
> and suppress such macros if __cplusplus is defined, even in the POSIX
> headers? But I think from an application portability perspective, they
> should either use #undef or parens, i.e. (::pthread_equal)(id1,id2),
> instead of assuming there is no macro.
>
> Rich
>From an application developer point of view I would look at the POSIX
specification which says pthread_equal is a function defined as:
int pthread_equal(pthread_t t1, pthread_t t2)
I also proposed the solution with the parentesis. But in my opinion it
is a little bit confusing for an application developer to assume a
function specified by POSIX may be implemented as a macro.
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