It needs to #include <errno.h> to get the macro definition of errno
in <sys/errno.h>. I'm surprised this test isn't broken on more
platforms.
Actually, that's not causing the problem the OP is seeing. <errno.h>
gets included by <pthread.h>, which causes errno to be defined as:
#define errno (*__error())
The problem is in the implementation of __error():
#undef errno
int *__error(void) {
pthread_t self = pthread_self();
/* If we're not a detached pthread, just return the global errno */
if ((self == (pthread_t)0) || (self->sig != _PTHREAD_SIG) ||
(self->detached & _PTHREAD_CREATE_PARENT)) {
return &errno;
}
return &self->err_no;
}
Libc has both global and per-thread errno values, which both get set
on return from a failed library call. The self->detached check above
is true in the case of the main thread, so the main thread always uses
the global errno value, and the global errno value is always set at
the same time the per-thread value is set.
While the window for this race *should* be small (programs are
supposed to only check errno immediately after a failed library call),
I've filed a bug against the "optimization" in the __error()
implementation...
matt.
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