Re: [boost] [boost.process] 0.6 Alpha

Subject: Re: [boost] [boost.process] 0.6 Alpha
From: Damien Buhl (damien.buhl_at_[hidden])
Date: 2016-06-21 02:05:12

On 21/06/2016 02:14, Gavin Lambert wrote:
> On 17/06/2016 21:45, Klemens Morgenstern wrote:
>>> But on the other hand from a library design point of view, shouldn't
>>> the
>>> library have the best smart default in terms of performance and
>>> overhead
>>> on a given platform ? Instead of having a flag telling : please do it
>>> the same but efficiently ? Because on linux vfork is nothing but
>>> obsoleted and for a scenario of using execve looks better to me.
>>
>> Again: obsolete and now removed in the posix-standard and that's what I
>> ought to go with. Please note, that I'm trying to provide two platforms:
>> Posix & Windows. Not Linux & Windows. Thereby I want to provide the most
>> common way for both platforms; and though I really appreciate your
>> scenario, I would not consider it the common way.
>
> Possibly of interest is that according to the notes vfork+exec (and
> fork+exec, for that matter) was deprecated in favour of posix_spawn.
> Which appears to be less well documented, but does exist in some
> environments at least.
>

Yes it's the code I quoted from the glibc, ( basically Boost.Process is
another posix_spawn, brought to another level though) :
> The rationale of posix_spawn here is a good addition to what we discuss
> I think :
> http://pubs.opengroup.org/onlinepubs/009695399/functions/posix_spawn.html#tag_03_427_08

In glibc /sysdeps/posix/spawni.c implementation of posix_spawn:

>   /* Generate the new process.  */
>   if ((flags & POSIX_SPAWN_USEVFORK) != 0
>       /* If no major work is done, allow using vfork.  Note that we
>      might perform the path searching.  But this would be done by
>      a call to execvp(), too, and such a call must be OK according
>      to POSIX.  */
>       || ((flags & (POSIX_SPAWN_SETSIGMASK | POSIX_SPAWN_SETSIGDEF
>             | POSIX_SPAWN_SETSCHEDPARAM | POSIX_SPAWN_SETSCHEDULER
>             | POSIX_SPAWN_SETPGROUP | POSIX_SPAWN_RESETIDS)) == 0
>       && file_actions == NULL))
>     new_pid = __vfork ();
>   else
>     new_pid = __fork ();
>