Hello,
in RTEMS there are three routines that can deliver signals to a thread:
rtems_signal_send(), _POSIX_signals_Unblock_thread() and pthread_kill().
It is possible to send signals from an interrupt service routine.
Signal handler invocation is an unconditional side-effect of _Thread_Dispatch().
Since many interrupt prologues evaluate _Thread_Dispatch_necessary before they
branch to _Thread_Dispatch() there is a special case in the signal notification
path. Here we have:
if ( _ISR_Is_in_progress() && _Thread_Is_executing( the_thread ) )
_Thread_Dispatch_necessary = true;
Now we have the following problem. Suppose we have a thread with non-preempt
mode.
An interrupt happens and unblocks another thread with a higher priority. The
normal scheduler will do this:
void _Scheduler_priority_Unblock (
Thread_Control *the_thread
)
{
_Scheduler_priority_Ready_queue_enqueue(the_thread);
/* TODO: flash critical section? */
/*
* If the thread that was unblocked is more important than the heir,
* then we have a new heir. This may or may not result in a
* context switch.
*
* Normal case:
* If the current thread is preemptible, then we need to do
* a context switch.
* Pseudo-ISR case:
* Even if the thread isn't preemptible, if the new heir is
* a pseudo-ISR system task, we need to do a context switch.
*/
if ( the_thread->current_priority < _Thread_Heir->current_priority ) {
_Thread_Heir = the_thread;
if ( _Thread_Executing->is_preemptible ||
the_thread->current_priority == 0 )
_Thread_Dispatch_necessary = true;
}
}
The heir is updated, but _Thread_Dispatch_necessary remains unchanged!
Now suppose an interrupt happens and sends a signal to the executing thread.
Now all conditions in
if ( _ISR_Is_in_progress() && _Thread_Is_executing( the_thread ) )
_Thread_Dispatch_necessary = true;
are satisfied and _Thread_Dispatch_necessary is set to true. This will result
in _Thread_Dispatch() being called and a context switch is performed to the
heir thread although the executing thread has the non-preempt mode!
Is this intentional?
--
Sebastian Huber, embedded brains GmbH
Address : Dornierstr. 4, D-82178 Puchheim, Germany
Phone : +49 89 189 47 41-16
Fax : +49 89 189 47 41-09
E-Mail : [email protected]
PGP : Public key available on request.
Diese Nachricht ist keine geschäftliche Mitteilung im Sinne des EHUG.
_______________________________________________
rtems-devel mailing list
[email protected]
http://www.rtems.org/mailman/listinfo/rtems-devel
