score: Simplify _Thread_Change_priority()

The function to change a thread priority was too complex.  Simplify it
with a new scheduler operation.  This increases the average case
performance due to the simplified logic.  The interrupt disabled
critical section is a bit prolonged since now the extract, update and
enqueue steps are executed atomically.  This should however not impact
the worst-case interrupt latency since at least for the Deterministic
Priority Scheduler this sequence can be carried out with a wee bit of
instructions and no loops.

Add _Scheduler_Change_priority() to replace the sequence of
  - _Thread_Set_transient(),
  - _Scheduler_Extract(),
  - _Scheduler_Enqueue(), and
  - _Scheduler_Enqueue_first().

Delete STATES_TRANSIENT, _States_Is_transient() and
_Thread_Set_transient() since this state is now superfluous.

With this change it is possible to get rid of the
SCHEDULER_SMP_NODE_IN_THE_AIR state.  This considerably simplifies the
implementation of the new SMP locking protocols.

1 files changed, 8 insertions, 9 deletions

diff --git a/cpukit/score/include/rtems/score/scheduler.h b/cpukit/score/include/rtems/score/scheduler.h
index 7f0b43ae52..b1e8f8ac4f 100644
--- a/cpukit/score/include/rtems/score/scheduler.h
+++ b/cpukit/score/include/rtems/score/scheduler.h
@@ -63,6 +63,14 @@ typedef struct {
   /** @see _Scheduler_Unblock() */
   void ( *unblock )( const Scheduler_Control *, Thread_Control * );
 
+  /** @see _Scheduler_Change_priority() */
+  void ( *change_priority )(
+    const Scheduler_Control *,
+    Thread_Control *,
+    Priority_Control,
+    bool
+  );
+
   /** @see _Scheduler_Allocate() */
   bool ( *allocate )( const Scheduler_Control *, Thread_Control * );
 
@@ -72,15 +80,6 @@ typedef struct {
   /** @see _Scheduler_Update() */
   void ( *update )( const Scheduler_Control *, Thread_Control * );
 
-  /** @see _Scheduler_Enqueue() */
-  void ( *enqueue )( const Scheduler_Control *, Thread_Control * );
-
-  /** @see _Scheduler_Enqueue_first() */
-  void ( *enqueue_first )( const Scheduler_Control *, Thread_Control * );
-
-  /** @see _Scheduler_Extract() */
-  void ( *extract )( const Scheduler_Control *, Thread_Control * );
-
   /** @see _Scheduler_Priority_compare() */
   int ( *priority_compare )(
     Priority_Control,