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.

9 files changed, 25 insertions, 34 deletions

diff --git a/cpukit/score/src/schedulercbsunblock.c b/cpukit/score/src/schedulercbsunblock.c
index 688253c279..56b35de8b9 100644
--- a/cpukit/score/src/schedulercbsunblock.c
+++ b/cpukit/score/src/schedulercbsunblock.c
@@ -79,10 +79,10 @@ Scheduler_Void_or_thread _Scheduler_CBS_Unblock(
        _Thread_Heir->current_priority
     )
   ) {
-    _Thread_Heir = the_thread;
-    if ( _Thread_Executing->is_preemptible ||
-         the_thread->current_priority == 0 )
-      _Thread_Dispatch_necessary = true;
+    _Scheduler_Update_heir(
+      the_thread,
+      the_thread->current_priority == PRIORITY_PSEUDO_ISR
+    );
   }
 
   SCHEDULER_RETURN_VOID_OR_NULL;
diff --git a/cpukit/score/src/scheduleredfchangepriority.c b/cpukit/score/src/scheduleredfchangepriority.c
index 3eabc83878..61e0481d03 100644
--- a/cpukit/score/src/scheduleredfchangepriority.c
+++ b/cpukit/score/src/scheduleredfchangepriority.c
@@ -39,5 +39,7 @@ Scheduler_Void_or_thread _Scheduler_EDF_Change_priority(
     false
   );
 
+  _Scheduler_EDF_Schedule_body( scheduler, the_thread, false );
+
   SCHEDULER_RETURN_VOID_OR_NULL;
 }
diff --git a/cpukit/score/src/scheduleredfunblock.c b/cpukit/score/src/scheduleredfunblock.c
index 308a691e64..977534214c 100644
--- a/cpukit/score/src/scheduleredfunblock.c
+++ b/cpukit/score/src/scheduleredfunblock.c
@@ -46,10 +46,10 @@ Scheduler_Void_or_thread _Scheduler_EDF_Unblock(
          scheduler,
          _Thread_Heir->current_priority,
          the_thread->current_priority )) {
-    _Thread_Heir = the_thread;
-    if ( _Thread_Executing->is_preemptible ||
-         the_thread->current_priority == 0 )
-      _Thread_Dispatch_necessary = true;
+    _Scheduler_Update_heir(
+      the_thread,
+      the_thread->current_priority == PRIORITY_PSEUDO_ISR
+    );
   }
 
   SCHEDULER_RETURN_VOID_OR_NULL;
diff --git a/cpukit/score/src/schedulerprioritychangepriority.c b/cpukit/score/src/schedulerprioritychangepriority.c
index 06c5f0f7c6..f883e02d43 100644
--- a/cpukit/score/src/schedulerprioritychangepriority.c
+++ b/cpukit/score/src/schedulerprioritychangepriority.c
@@ -59,5 +59,7 @@ Scheduler_Void_or_thread _Scheduler_priority_Change_priority(
     );
   }
 
+  _Scheduler_priority_Schedule_body( scheduler, the_thread, false );
+
   SCHEDULER_RETURN_VOID_OR_NULL;
 }
diff --git a/cpukit/score/src/schedulerpriorityunblock.c b/cpukit/score/src/schedulerpriorityunblock.c
index 06d29f3b91..a912ebfbe2 100644
--- a/cpukit/score/src/schedulerpriorityunblock.c
+++ b/cpukit/score/src/schedulerpriorityunblock.c
@@ -52,10 +52,10 @@ Scheduler_Void_or_thread _Scheduler_priority_Unblock (
    *    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;
+    _Scheduler_Update_heir(
+      the_thread,
+      the_thread->current_priority == PRIORITY_PSEUDO_ISR
+    );
   }
 
   SCHEDULER_RETURN_VOID_OR_NULL;
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;
 }
diff --git a/cpukit/score/src/schedulersimplechangepriority.c b/cpukit/score/src/schedulersimplechangepriority.c
index b8638ad28c..9b94b3ab26 100644
--- a/cpukit/score/src/schedulersimplechangepriority.c
+++ b/cpukit/score/src/schedulersimplechangepriority.c
@@ -39,5 +39,7 @@ Scheduler_Void_or_thread _Scheduler_simple_Change_priority(
     _Scheduler_simple_Insert_priority_fifo( &context->Ready, the_thread );
   }
 
+  _Scheduler_simple_Schedule_body( scheduler, the_thread, false );
+
   SCHEDULER_RETURN_VOID_OR_NULL;
 }
diff --git a/cpukit/score/src/schedulersimpleunblock.c b/cpukit/score/src/schedulersimpleunblock.c
index 6f9b2f719f..a020f74767 100644
--- a/cpukit/score/src/schedulersimpleunblock.c
+++ b/cpukit/score/src/schedulersimpleunblock.c
@@ -44,10 +44,10 @@ Scheduler_Void_or_thread _Scheduler_simple_Unblock(
    *    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;
+    _Scheduler_Update_heir(
+      the_thread,
+      the_thread->current_priority == PRIORITY_PSEUDO_ISR
+    );
   }
 
   SCHEDULER_RETURN_VOID_OR_NULL;
diff --git a/cpukit/score/src/threadchangepriority.c b/cpukit/score/src/threadchangepriority.c
index ca2c5871af..d61dfb859a 100644
--- a/cpukit/score/src/threadchangepriority.c
+++ b/cpukit/score/src/threadchangepriority.c
@@ -46,17 +46,10 @@ void _Thread_Change_priority(
         new_priority,
         prepend_it
       );
-
-      _ISR_Flash( level );
-
-      /*
-       *  We altered the set of thread priorities.  So let's figure out
-       *  who is the heir and if we need to switch to them.
-       */
-      _Scheduler_Schedule( the_thread );
     } else {
       _Scheduler_Update_priority( the_thread, new_priority );
     }
+
     _ISR_Enable( level );
 
     _Thread_queue_Requeue( the_thread->Wait.queue, the_thread );