Re: [Xenomai-help] handling threads within a pod

[Philippe Gerum <rpm@xenomai.org>]

On Thu, 2006-07-13 at 10:41 +0200, Khalil GHORBAL wrote:

> I'll give an example to explain the issue:
> Assuming having multiple threads in our active pod, these threads can be 
> in different states.
> The running thread have to get the *extinfo* field of thread named 
> "COM_THREAD" (for example) if exists.
> 
> All services of the nucleus need a *xnthread_t* structure to identify 
> the thread to treat, we can't have a list or something similar to sweep 
> existing threads. All I've found is the global queue, doubly-linked and 
> circular, which link all threads.
> So all informations I have is the number of threads and a way to go from 
> one holder to another
> without really be able to identify the thread and read the other fields.
> 

Forget about extinfo; you don't need this, and it's old cruft we are
going to kill in later versions anyway. What you need to handle
arinc653-like temporal partitioning is something along these lines:

struct ima380_process {
	xnthread_t threadbase;	/* process control block */
	xnholder_t ptlink;	/* link to next partition */
	/* ... */
};

struct ima380_partition {
	xnqueue_t procq;	/* chains ima380 processes */
	/* ... */
};

Don't refer to Xenomai's global thread queue, just manage your own
process queues populating a partition object abstraction.

Then use the XNHELD bit which has been specifically added as a
suspensive condition to handle temporal partitioning. This way, XNSUSP
remains available for suspending processes forcibly within a partition
(suspension bits are conjunctive). IOW, only the processes pertaining to
the running partition will have the XNHELD bit cleared, others will have
this bit set, and as such, suspended by the nucleus, which is what you
want.

void deactivate_partition (struct ima380_partition *pt)
{
	foreach(thread in pt->procq) {
		xnpod_suspend_thread(thread,XNHELD,XN_INFINITE,NULL);
	}
}

void activate_partition (struct ima380_partition *pt)
{
	foreach(thread in pt->procq) {
		xnpod_resume_thread(thread,XNHELD);
	}
}

The partition slicer can be implemented as a simple periodic timer,
whose handler activates existing partitions in a round-robin fashion.

FWIW, mimicking arinc653 over the nucleus is a no-brainer, so there's
good hope for IMA380.

-- 
Philippe.