This is the mail archive of the
cygwin
mailing list for the Cygwin project.
RE: pthread_attr_init() returning errors
- From: "Canham, Timothy K (348C)" <timothy dot k dot canham at jpl dot nasa dot gov>
- To: "cygwin at cygwin dot com" <cygwin at cygwin dot com>
- Date: Wed, 20 Apr 2016 14:20:25 +0000
- Subject: RE: pthread_attr_init() returning errors
- Authentication-results: sourceware.org; auth=none
- References: <E8EB3633A6A4594CA063A3FCBC82C18C3621F0F6 at ap-embx-sp40 dot RES dot AD dot JPL> <20160420105016 dot GB26118 at calimero dot vinschen dot de>
So what you are saying is that when pthread_attr_init() checked for the magic number in supposedly uninitialized memory it found the exact value of the magic number? That seems highly suspect. Seems like it may be pointing to a valid previous entry.
Tim Canham
JPL Flight Software
-----Original Message-----
From: Corinna Vinschen [mailto:corinna-cygwin@cygwin.com]
Sent: Wednesday, April 20, 2016 3:50 AM
To: cygwin@cygwin.com
Cc: Canham, Timothy K (348C) <timothy.k.canham@jpl.nasa.gov>
Subject: Re: pthread_attr_init() returning errors
On Apr 19 19:49, Canham, Timothy K (348C) wrote:
> I have some code to start a task that suddenly started failing. This
> is pretty mature code. Here is the code fragment with my added
> printf()
>
> pthread_attr_t att;
> int stat = pthread_attr_init(&att);
> if (stat != 0) {
> printf("pthread_attr_init: (%d)(%d): %s\n",stat,errno,strerror(stat));
> // return
> }
>
> Here is the output:
>
> 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 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 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
--
Corinna Vinschen Please, send mails regarding Cygwin to
Cygwin Maintainer cygwin AT cygwin DOT com
Red Hat