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Re: [Bug] __wait_status_to_int() is expected to be a macro




On 06/08/2018 12:26 PM, Hans-Bernhard Bröker wrote:
Am 08.06.2018 um 17:16 schrieb Denis Nikiforov:
/usr/include/boost/process/detail/posix/is_running.hpp:18:1: error:
non-constant condition for static assertion
  static_assert(!WIFEXITED(still_active), "Internal Error");
  ^~~~~~~~~~~~~

__wait_status_to_int must be a macros but it's redefined as a function.

It must?  Says who, based on what standard document?

For starters, nobody gets to make any such claims about __wait_status_to_int(), because that's an internal implementation detail of Cygwin.  If at all, such a claim might be made about WIFEXITED(), which is a POSIX standard element.  But POSIX makes no such requirement, as far as I could see on short examination.

POSIX requires:

http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/sys_wait.h.html#tag_13_71

"The <sys/wait.h> header shall define the following macros for analysis of process status values:

WEXITSTATUS
    Return exit status.
WIFCONTINUED
    [XSI] [Option Start] True if child has been continued. [Option End]
WIFEXITED
    True if child exited normally.
..."

and:

http://pubs.opengroup.org/onlinepubs/9699919799/functions/waitpid.html

"Regardless of its value, this information may be interpreted using the following macros, which are defined in <sys/wait.h> and evaluate to integral expressions; the stat_val argument is the integer value pointed to by stat_loc.

WIFEXITED(stat_val)
Evaluates to a non-zero value if status was returned for a child process that terminated normally.
WEXITSTATUS(stat_val)"


Nothing in that wording requires WIFEXITED(foo) to be a compile-time constant if foo is also a compile-time constant, so on that grounds, Boost is buggy for trying to assume that WIFEXITED(constant) can be used in a static_assert(). On the other hand, the implementation of WIFEXITED() is more like Linux if it DOES result in a compile-time constant when used on a compile-time constant argument; so in that regards, it would ALSO be worth patching Cygwin, whether or not the Boost portability bug is fixed.

--
Eric Blake, Principal Software Engineer
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