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Date: Mon, 25 Aug 2008 18:51:47 +0200
From: Philippe Gerum <rpm@xenomai.org>
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Subject: Re: [Xenomai-help] rt_queue_delete returns -EBUSY
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To: Petr Cervenka <grugh@domain.hid>
Cc: xenomai@xenomai.org

Petr Cervenka wrote:
> Hello,
> I tried xenomai 2.4.5, hoping that my problems with real-time queue will disappear. But there is another (perhaps very trivial) error.
> Function call rt_queue_delete always returns -EBUSY (at least for me). You don't have to bind it from another task or use it at all.
> I hope that I have used it in the right way.

Actually, if your code still creates and deletes queues dynamically during the
normal operations, this is clearly not the best approach. Those calls are VERY
costly, and very much prone to unbounded latency.

I.e. They switch to secondary mode, allocate/deallocate ranges of kernel memory,
create/delete internal Xenomai heap objects, and eventually map/unmap those
memory ranges to/from your user-space process.

> Petr Cervenka
> 
> Simple example:
> 
> #include <stdlib.h>
> 
> #include <sys/mman.h>       // mlockall
> #include <native/task.h>
> #include <native/queue.h>
> 
> RT_TASK  main_task;
> RT_QUEUE queue;
> 
> int main(int argc, char** argv) {
>     int res;
>     
>     mlockall(MCL_CURRENT | MCL_FUTURE);
>     
>     res = rt_task_shadow(&main_task, "MAIN_TASK", 5, T_FPU);
>     if (res < 0) {
>         fprintf(stderr, "rt_task_shadow() failed: %d (%s)\n", res, strerror(-res));
>         goto cleanup_end;
>     }
>     
>     res = rt_queue_create(&queue, "QUEUE", 1024, Q_UNLIMITED, Q_FIFO | Q_SHARED);
>     if (res < 0) {
>         fprintf(stderr, "rt_queue_create() failed: %d (%s)\n", res, strerror(-res));
>         goto cleanup_task;
>     }
>     
> cleanup_queue:
>     res = rt_queue_delete(&queue);
>     if (res < 0) {
>         fprintf(stderr, "rt_queue_delete() failed: %d (%s)\n", res, strerror(-res));
>     }
> cleanup_task:
> cleanup_end:
>     return res;
> } 
> 
> 
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> 


-- 
Philippe.