Re: [Xenomai] race condition when creating and deleting VxWorks tasks in xenomai-forge

[Philippe Gerum <rpm@xenomai.org>]

On 02/04/2014 08:12 PM, Matthias Schneider wrote:
> the patch seems to address the original problem. Should this patch be merged
> into the repository?
>

It is on its way to 'master', currently pending in 'next'.

> However, I seem to stumble into a different problem. If I understand correctly,
> CANCEL_DEFER() should prevent the thread/task from being cancelled.

...asynchronously. This is the important missing part.

I have verified
> that pthread_setcanceltype() is being entered and the CONFIG_XENO_ASYNC_CANCEL
> macro has thus been set correctly. Nevertheless, putting a printf after CANCEL_DEFER
> and before CANCEL_RESTORE shows that when rapidly creating and destroying tasks
> the CANCEL_RESTORE printf is not printed. Also, I run into a deadlock very quickly,
> due to wind_task_lock being held (consistent with the observed printf behavior).
> I am using Mercury on top on an unpatched linux kernel. Any idea how I can debug the
> apparently non-functioning pthread_setcanceltype ?
>

Per POSIX, printf() is a cancellation point, any pending cancellation 
request will be handled unconditionally when traversing it. CANCEL_DEFER 
will only postpone async cancellation requests, until a cancellation 
point is traversed or async cancellation mode is enabled back, whichever 
comes first.

http://pubs.opengroup.org/onlinepubs/009695399/functions/xsh_chap02_09.html

-- 
Philippe.