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, 41 insertions, 0 deletions

diff --git a/cpukit/score/src/schedulersimplechangepriority.c b/cpukit/score/src/schedulersimplechangepriority.c
new file mode 100644
index 0000000000..010f1dfc79
--- /dev/null
+++ b/cpukit/score/src/schedulersimplechangepriority.c
@@ -0,0 +1,41 @@
+/**
+ * @file
+ *
+ * @brief Removes a Thread from the Simple Queue
+ *
+ * @ingroup ScoreScheduler
+ */
+
+/*
+ *  COPYRIGHT (c) 2011.
+ *  On-Line Applications Research Corporation (OAR).
+ *
+ *  The license and distribution terms for this file may be
+ *  found in the file LICENSE in this distribution or at
+ *  http://www.rtems.org/license/LICENSE.
+ */
+
+#if HAVE_CONFIG_H
+#include "config.h"
+#endif
+
+#include <rtems/score/schedulersimpleimpl.h>
+
+void _Scheduler_simple_Change_priority(
+  const Scheduler_Control *scheduler,
+  Thread_Control          *the_thread,
+  Priority_Control         new_priority,
+  bool                     prepend_it
+)
+{
+  Scheduler_simple_Context *context =
+    _Scheduler_simple_Get_context( scheduler );
+
+  _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 );
+  }
+}