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Date: Sun, 31 Aug 2014 21:10:46 +0200
From: Jens Gustedt <>
Subject: Re: [PATCH 7/8] add the thrd_xxxxxx functions

Am Sonntag, den 31.08.2014, 13:02 -0400 schrieb Rich Felker:
> On Sun, Aug 31, 2014 at 06:36:00PM +0200, Jens Gustedt wrote:
> > EAGAIN from clone is clearly a distinct error condition than when it
> > is on ENOMEM. I would not see it covered by what C11 expects as that
> > error condition. So the EAGAIN from clone should go to thrd_error, I
> > think, and not be merged with ENOMEM for the C threads implementation.
> I disagree here, at least unless you have a convincing argument for
> this. EAGAIN from clone reflects a condition where a resource could
> not be allocated. The reason (policy or inherent limits on a
> particular type of resource, as opposed to just generally running out
> of memory) doesn't seem to be relevant to applications, and I don't
> see how thrd_error is any more appropriate than thrd_nomem for
> reporting it. Certainly there are other cases where one type of
> allocation (e.g. mmap for a thread) might fail where another (e.g.
> malloc reusing freed memory on the heap) might fail, so I don't think
> you can say that thrd_nomem is inappropriate if malloc would succeed.

The convincing arguments come from the documentation, I'd say. C11

  The thrd_create function returns

   thrd_success on success, or

   thrd_nomem if no memory could be allocated for the thread requested, or

   thrd_error if the request could not be honored.

(If this is a reasonable distinction of errors is a completely
different question.)

The man page for clone (whatever authority this has) says, among other

       EAGAIN Too many processes are already running.

       ENOMEM Cannot allocate sufficient memory to allocate a task
              structure for the child, or to copy those parts of the
              caller's context that need to be copied.

I have difficulties to read "lack of other resources" into the case
for thrd_nomem. I see that EAGAIN is relatively well covered by
thrd_error, but not very well by thrd_nomem. thrd_nomem is the
catch-all-the-rest error, so I think that C11 permits to map EAGAIN
together with eventually happening other exotic stuff on on it.


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