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Re: [libvirt] [PATCH] virthreadpthread: don't try to cast pthread_t to void*



At Thu, 02 May 2013 07:54:47 -0600,
Eric Blake wrote:
> 
> [1  <multipart/signed (7bit)>]
> [1.1  <text/plain; UTF-8 (quoted-printable)>]
> On 05/02/2013 06:05 AM, Guido Günther wrote:
> > This fixes the build on kFreeBSD that otherwise fails with:
> > 
> > util/virthreadpthread.c: In function 'virThreadSelfID':
> > util/virthreadpthread.c:222:27: error: cast from function call of type 'pthread_t' to non-matching type 'void *' [-Werror=bad-function-cast]
> > ---
> > I'm unsure why we'd need the cast to (void*) first.
> 
> EVERYTHING should be castable to void*.  That's lame that your compiler
> is refusing to cast pthread_t.
> 
> I'm thinking that the solution will require writing a union, assign to
> the pthread_t member of the union, and read out the int member, as the
> only way we're going to shut up compilers.  We KNOW that casting
> pthread_t isn't portable; but all we really want is a few bits that are
> hopefully likely enough to be unique to make the use of virThreadSelfID
> useful in debug messages.  We aren't relying on the conversion being a
> 1:1 mapping nor on trying to reverse the mapping.

Since the warning only ever refers to directly casting a function
return value, wouldn't it suffice to introduce a (properly typed)
variable first assigning the function result?

pthread_t self = pthread_self();
return (int)(intptr_t)self;

Just my 2¢
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