On 04/19/2016 04:31 PM, Philippe Gerum wrote:
On 04/19/2016 04:08 PM, Andrea wrote:
Hello,
I'm currently trying to integrate Xenomai 3.0.2 using Cobalt with alchemy
skin in a C++ project, under kernel 4.1.8 with i-pipe patch.
In my application I'm creating some threads using boost library, and I
would like to shadow one of them to a rt_task in order to use some
xenomai
function in there.
If I call rt_task_shadow(NULL, NULL, 0,0) from the running thread,
-EINVAL
is returned.
While the API docs says that this can be due to an invalid prio, tracking
down the source of the error, it appears that in my case it is
generated in
the function syncobj_lock (copperplate/syncobj.c), where a call to
monitor_enter (which internally calls cobalt_monitor_enter) fails and
returns -1.
The same happens with threads created both using standard
pthread_create or
via the boost library.
Trying to shadow the main thread (or creating rt_task from there) works
correctly. instead.
A reproducible example in my system:
#include "pthread.h"
#include "alchemy/task.h"
#include <iostream>
#include <unistd.h>
void* shadow(void*)
{
std::cerr<<"Shadow returned "<< rt_task_shadow(NULL, NULL, 0,0);
}
int main(int argc, char* argv[])
{
pthread_t test_thread;
// new boost::thread(shadow);
pthread_create(&test_thread, NULL, shadow, NULL);
sleep(10);
return 0;
}
with output: Shadow returned -22
Do you have any insight on where the problem could be? Am I missing
something basic?
I suspect some chicken and egg situation in the rt_task_shadow()
implementation. I'll have a look as soon as I can.
If possible, I would like to stick to alchemy skin.
Unfortunately, the only way to work around this issue at the moment
would be to call libcobalt's pthread_setschedparam() for pthread_self(),
until this issue is fixed in libalchemy. You could do this for a
particular statement without wrapping the POSIX API by calling:
struct sched_param parm = { .sched_priority = 0 };
__RT(pthread_setschedparam(phread_self(), SCHED_OTHER, &parm);
instead of rt_task_shadow(). libcobalt is underlying all Xenomai 3
applications, so you would not need to fixup the build rules or
dependencies. It's already there.
Ok, so my suspicion turned out to be true, rt_task_shadow() used to call
Cobalt services for creating ... a Cobalt context, which is not exactly
a bright idea. This is fixed in the stable- and next- branches.
However, rt_task_create() is still not usable from a plain regular POSIX
thread; this could be done, but at the expense of significant changes
that do not seem worth it, given that calling __STD(pthread_create())
followed by running rt_task_shadow() from the created regular pthread
would lead to the same result than creating a real-time thread directly
from a regular pthread context.
The rationale is that a main thread is automatically turned into a
Cobalt thread during early init, prior to entering the main() routine
(unless automatic Xenomai bootstrap was disabled though). Therefore an
application may fully instantiate the system, calling any Xenomai
service over the main() context to do so.
rt_task_shadow() (as fixed) should be used to turn a plain pthread
context into a Xenomai thread, before the latter invokes other calls
from the Alchemy API.
--
Philippe.
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