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X-HELO: calimero.vinschen.de
Date: Wed, 20 Apr 2016 12:50:16 +0200
From: Corinna Vinschen <corinna-cygwin AT cygwin DOT com>
To: cygwin AT cygwin DOT com
Cc: "Canham, Timothy K (348C)" <timothy DOT k DOT canham AT jpl DOT nasa DOT gov>
Subject: Re: pthread_attr_init() returning errors
Message-ID: <20160420105016.GB26118@calimero.vinschen.de>
Reply-To: cygwin AT cygwin DOT com
Mail-Followup-To: cygwin AT cygwin DOT com,	"Canham, Timothy K (348C)" <timothy DOT k DOT canham AT jpl DOT nasa DOT gov>
References: <E8EB3633A6A4594CA063A3FCBC82C18C3621F0F6 AT ap-embx-sp40 DOT RES DOT AD DOT JPL>
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On Apr 19 19:49, Canham, Timothy K (348C) wrote:
> I have some code to start a task that suddenly started failing. This is p=
retty mature code. Here is the code fragment with my added printf()
>=20
>         pthread_attr_t att;
>         int stat =3D pthread_attr_init(&att);
>         if (stat !=3D 0) {
>             printf("pthread_attr_init: (%d)(%d): %s\n",stat,errno,strerro=
r(stat));
>             // return
>         }
>=20
> Here is the output:
>=20
> pthread_attr_init: (16)(0): Device or resource busy

This is most unusual.  What happens is this:

A pthread_attr_t is a pointer to a pointer to a struct with a magic
number.  And at the start of pthread_attr_init this magic number is
tested if it's already the magic number expected for an object of type
pthread_attr_t.  And only if so, the pthread_attr_init function fails
with EBUSY.

That means, the arbitrary value in the uninitialized att prior to=20
the call to pthread_attr_init is a pointer value which points to
valid memory which has the magic value 0xdf0df048.  Wow.

This means we can't keep up with the tests in the pthread_FOO_init
functions since they could point to an *supposedly* initialized=20
object, while in fact the value they point to is only accidentally
so that it looks like an initialized object.

I provided new developer snapshots on https://cygwin.com/snapshots/
and I've just uploaded a 2.5.1-0.1 test release which you can install
via setup as soon as your mirror has catched up.

Pleaser give any of them a try.


Thanks,
Corinna

--=20
Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Maintainer                 cygwin AT cygwin DOT com
Red Hat

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