score: Update _Thread_Heir only if necessary

Previously, the _Thread_Heir was updated unconditionally in case a new
heir was determined.  The _Thread_Dispatch_necessary was only updated in
case the executing thread was preemptible or an internal thread was
unblocked.  Change this to update the _Thread_Heir and
_Thread_Dispatch_necessary only in case the currently selected heir
thread is preemptible or a dispatch is forced.  Move the schedule
decision into the change priority operation and use the schedule
operation only in rtems_task_mode() in case preemption is enabled or an
ASR dispatch is necessary.  This is a behaviour change.  Previously, the
RTEMS_NO_PREEMPT also prevented signal delivery in certain cases (not
always).  Now, signal delivery is no longer influenced by
RTEMS_NO_PREEMPT.  Since the currently selected heir thread is used to
determine if a new heir is chosen, non-preemptible heir threads
currently not executing now prevent a new heir.  This may have an
application impact, see change test tm04.  Document this change in sp04.

Update #2273.

1 files changed, 2 insertions, 10 deletions

diff --git a/cpukit/score/src/schedulerpriorityyield.c b/cpukit/score/src/schedulerpriorityyield.c
index 2ee2d03057..5dab094f46 100644
--- a/cpukit/score/src/schedulerpriorityyield.c
+++ b/cpukit/score/src/schedulerpriorityyield.c
@@ -29,20 +29,12 @@ Scheduler_Void_or_thread _Scheduler_priority_Yield(
   Scheduler_priority_Node *node = _Scheduler_priority_Thread_get_node( the_thread );
   Chain_Control *ready_chain = node->Ready_queue.ready_chain;
 
-  (void) scheduler;
-
   if ( !_Chain_Has_only_one_node( ready_chain ) ) {
     _Chain_Extract_unprotected( &the_thread->Object.Node );
     _Chain_Append_unprotected( ready_chain, &the_thread->Object.Node );
-
-    if ( _Thread_Is_heir( the_thread ) ) {
-      _Thread_Heir = (Thread_Control *) _Chain_First( ready_chain );
-    }
-
-    _Thread_Dispatch_necessary = true;
-  } else if ( !_Thread_Is_heir( the_thread ) ) {
-    _Thread_Dispatch_necessary = true;
   }
 
+  _Scheduler_priority_Schedule_body( scheduler, the_thread, true );
+
   SCHEDULER_RETURN_VOID_OR_NULL;
 }