Date: Thu, 17 Jul 2014 15:57:35 -0400 From: Garrett Wollman <wollman@csail.mit.edu> To: yaneurabeya@gmail.com Cc: freebsd-standards@FreeBSD.org Subject: Re: [Bug 191906] New: pthread_cancel(NULL) on FreeBSD returns EINVAL, not ESRCH according to manpage Message-ID: <21448.10927.483892.974746@khavrinen.csail.mit.edu> In-Reply-To: <bug-191906-15@https.bugs.freebsd.org/bugzilla/> References: <bug-191906-15@https.bugs.freebsd.org/bugzilla/>
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<<On Thu, 17 Jul 2014 03:13:01 +0000, bugzilla-noreply@freebsd.org said:
> According to pthread_cancel(3) and opengroup, pthread_cancel should
> only return ESRCH, not EINVAL (but it apparently returns EINVAL for
> thread=NULL).
According to my copy of SUSv7 (1003.1-2008):
RETURN VALUE
If successful, the pthread_cancel ( ) function shall return zero; otherwise, an error number shall be
returned to indicate the error.
ERRORS
The pthread_cancel ( ) function shall not return an error code of [EINTR].
That is the entirety of what it says about errors for
pthread_cancel(). (Page 1572 in the SUSv7 PDF for those following at
home.)
SUSv6 (1003.1-2001) said something different:
ERRORS
The pthread_cancel ( ) function may fail if:
[ESRCH] No thread could be found corresponding to that specified by the given thread
ID.
The pthread_cancel ( ) function shall not return an error code of [EINTR].
This error was removed, and passing an invalid pthread_t value to
pthread_cancel() is now UNDEFINED in SUSv7. This was changed because
pthread_t is a pointer in some branded Unix systems (as well as
FreeBSD), and SUSv6 mistakenly required pthread_t to be an arithmetic
type. It was felt that these implementations should not be required
to validate pthread_t values -- they should be entitled to rely on C's
usual lack-of-semantics for invalid pointers. (Recall that in C,
merely *loading* an invalid pointer causes undefined behavior, so you
clearly are already in UB territory if you try to pass one to a
function.)
The test you cite is simply wrong, albeit for the opposite reason:
int
main(void)
{
int rv = pthread_cancel(NULL);
printf("%s\n", strerror(rv));
return (0);
}
There is no guarantee that NULL can be converted to pthread_t, and
applications are not allowed to "look inside" the typedef and use the
special properties of the underlying type.
-GAWollman
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