score: Support scheduler change inhibitors

For example, the POSIX sporadic server adds a second priority to a
thread.  We cannot account for this priority in a scheduler change.

Update #5164.

cpukit/include/rtems/score/schedulerimpl.h

@@ -942,6 +942,12 @@ static inline Status_Control _Scheduler_Set(
 
 #endif
 
+#if defined(RTEMS_SCORE_THREAD_HAS_SCHEDULER_CHANGE_INHIBITORS)
+  if ( the_thread->is_scheduler_change_inhibited ) {
+    return STATUS_RESOURCE_IN_USE;
+  }
+#endif
+
   if ( the_thread->Wait.queue != NULL ) {
     return STATUS_RESOURCE_IN_USE;
   }

cpukit/include/rtems/score/thread.h

@@ -112,6 +112,16 @@ extern "C" {
 #define RTEMS_SCORE_THREAD_REAL_PRIORITY_MAY_BE_INACTIVE
 #endif
 
+#if defined(RTEMS_POSIX_API) && defined(RTEMS_SMP)
+/**
+ * @brief This define enables support to inhibit scheduler changes.
+ *
+ * For example, the POSIX sporadic server adds a second priority to a thread.
+ * We cannot account for this priority in a scheduler change.
+ */
+#define RTEMS_SCORE_THREAD_HAS_SCHEDULER_CHANGE_INHIBITORS
+#endif
+
 /**
  *  @brief Type of the numeric argument of a thread entry function with at
  *  least one numeric argument.
@@ -911,6 +921,16 @@ struct _Thread_Control {
    */
   bool was_created_with_inherited_scheduler;
 
+#if defined(RTEMS_SCORE_THREAD_HAS_SCHEDULER_CHANGE_INHIBITORS)
+  /**
+   * @brief This field is true, if scheduler changes are inhibited.
+   *
+   * Currently, the POSIX sporadic server is the only inhibitor.  If more are
+   * added, then this needs to be changed to a counter or a bit field.
+   */
+  bool is_scheduler_change_inhibited;
+#endif
+
   /**
    * @brief This member contains the CPU budget control used to manage the CPU
    *   budget of the thread.

cpukit/posix/src/pthreadcreate.c

@@ -301,6 +301,9 @@ int pthread_create(
     the_attr->schedparam.sched_ss_max_repl;
 
   if ( schedpolicy == SCHED_SPORADIC ) {
+#if defined(RTEMS_SCORE_THREAD_HAS_SCHEDULER_CHANGE_INHIBITORS)
+    the_thread->is_scheduler_change_inhibited = true;
+#endif
     _POSIX_Threads_Sporadic_timer( &api->Sporadic.Timer );
   }
 #endif

cpukit/posix/src/pthreadsetschedparam.c

@@ -78,6 +78,10 @@ static int _POSIX_Set_sched_param(
     return EINVAL;
   }
 
+#if defined(RTEMS_SCORE_THREAD_HAS_SCHEDULER_CHANGE_INHIBITORS)
+  the_thread->is_scheduler_change_inhibited = ( policy == SCHED_SPORADIC );
+#endif
+
 #if defined(RTEMS_POSIX_API)
   if ( policy == SCHED_SPORADIC ) {
     low_prio = param->sched_ss_low_priority;