score: Rework _Thread_Change_priority()

Move the writes to Thread_Control::current_priority and
Thread_Control::real_priority into _Thread_Change_priority() under the
protection of the thread lock.  Add a filter function to
_Thread_Change_priority() to enable specialized variants.

Avoid race conditions during a thread priority restore with the new
Thread_Control::priority_restore_hint for an important average case
optimizations used by priority inheritance mutexes.

Update #2273.

1 files changed, 50 insertions, 4 deletions

diff --git a/cpukit/score/include/rtems/score/thread.h b/cpukit/score/include/rtems/score/thread.h
index b6662e49af..39fcb1707f 100644
--- a/cpukit/score/include/rtems/score/thread.h
+++ b/cpukit/score/include/rtems/score/thread.h
@@ -366,9 +366,21 @@ typedef struct {
   Objects_Control          Object;
   /** This field is the current execution state of this proxy. */
   States_Control           current_state;
-  /** This field is the current priority state of this proxy. */
+
+  /**
+   * @brief This field is the current priority state of this thread.
+   *
+   * Writes to this field are only allowed in _Thread_Initialize() or via
+   * _Thread_Change_priority().
+   */
   Priority_Control         current_priority;
-  /** This field is the base priority of this proxy. */
+
+  /**
+   * @brief This field is the base priority of this thread.
+   *
+   * Writes to this field are only allowed in _Thread_Initialize() or via
+   * _Thread_Change_priority().
+   */
   Priority_Control         real_priority;
 
   /**
@@ -379,6 +391,17 @@ typedef struct {
    */
   uint32_t                 priority_generation;
 
+  /**
+   * @brief Hints if a priority restore is necessary once the resource count
+   * changes from one to zero.
+   *
+   * This is an optimization to speed up the mutex surrender sequence in case
+   * no attempt to change the priority was made during the mutex ownership.  On
+   * SMP configurations atomic fences must synchronize writes to
+   * Thread_Control::priority_restore_hint and Thread_Control::resource_count.
+   */
+  bool                     priority_restore_hint;
+
   /** This field is the number of mutexes currently held by this proxy. */
   uint32_t                 resource_count;
 
@@ -653,9 +676,21 @@ struct Thread_Control_struct {
   Objects_Control          Object;
   /** This field is the current execution state of this thread. */
   States_Control           current_state;
-  /** This field is the current priority state of this thread. */
+
+  /**
+   * @brief This field is the current priority state of this thread.
+   *
+   * Writes to this field are only allowed in _Thread_Initialize() or via
+   * _Thread_Change_priority().
+   */
   Priority_Control         current_priority;
-  /** This field is the base priority of this thread. */
+
+  /**
+   * @brief This field is the base priority of this thread.
+   *
+   * Writes to this field are only allowed in _Thread_Initialize() or via
+   * _Thread_Change_priority().
+   */
   Priority_Control         real_priority;
 
   /**
@@ -666,6 +701,17 @@ struct Thread_Control_struct {
    */
   uint32_t                 priority_generation;
 
+  /**
+   * @brief Hints if a priority restore is necessary once the resource count
+   * changes from one to zero.
+   *
+   * This is an optimization to speed up the mutex surrender sequence in case
+   * no attempt to change the priority was made during the mutex ownership.  On
+   * SMP configurations atomic fences must synchronize writes to
+   * Thread_Control::priority_restore_hint and Thread_Control::resource_count.
+   */
+  bool                     priority_restore_hint;
+
   /** This field is the number of mutexes currently held by this thread. */
   uint32_t                 resource_count;
   /** This field is the blocking information for this thread. */