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, 13 insertions, 4 deletions

diff --git a/cpukit/score/src/schedulersimplereadyqueueenqueue.c b/cpukit/score/src/schedulersimplechangepriority.c
index 8e5f12d6ee..010f1dfc79 100644
--- a/cpukit/score/src/schedulersimplereadyqueueenqueue.c
+++ b/cpukit/score/src/schedulersimplechangepriority.c
@@ -1,7 +1,8 @@
 /**
  * @file
  *
- * @brief Scheduler Simple Priority Enqueue Ready Thread
+ * @brief Removes a Thread from the Simple Queue
+ *
  * @ingroup ScoreScheduler
  */
 
@@ -20,13 +21,21 @@
 
 #include <rtems/score/schedulersimpleimpl.h>
 
-void _Scheduler_simple_Ready_queue_enqueue(
+void _Scheduler_simple_Change_priority(
   const Scheduler_Control *scheduler,
-  Thread_Control          *the_thread
+  Thread_Control          *the_thread,
+  Priority_Control         new_priority,
+  bool                     prepend_it
 )
 {
   Scheduler_simple_Context *context =
     _Scheduler_simple_Get_context( scheduler );
 
-  _Scheduler_simple_Insert_priority_fifo( &context->Ready, the_thread );
+  _Scheduler_simple_Extract( scheduler, the_thread );
+
+  if ( prepend_it ) {
+    _Scheduler_simple_Insert_priority_lifo( &context->Ready, the_thread );
+  } else {
+    _Scheduler_simple_Insert_priority_fifo( &context->Ready, the_thread );
+  }
 }