score: Implement scheduler helping protocol

The following scheduler operations return a thread in need for help

    - unblock,
    - change priority, and
    - yield.

A thread in need for help is a thread that encounters a scheduler state
change from scheduled to ready or a thread that cannot be scheduled in
an unblock operation.  Such a thread can ask threads which depend on
resources owned by this thread for help.

Add a new ask for help scheduler operation.  This operation is used by
_Scheduler_Ask_for_help() to help threads in need for help returned by
the operations mentioned above.  This operation is also used by
_Scheduler_Thread_change_resource_root() in case the root of a resource
sub-tree changes.  A use case is the ownership change of a resource.

In case it is not possible to schedule a thread in need for help, then
the corresponding scheduler node will be placed into the set of ready
scheduler nodes of the scheduler instance.  Once a state change from
ready to scheduled happens for this scheduler node it may be used to
schedule the thread in need for help.

1 files changed, 3 insertions, 0 deletions

diff --git a/cpukit/score/src/threadinitialize.c b/cpukit/score/src/threadinitialize.c
index e6c4985591..e56e4e6cda 100644
--- a/cpukit/score/src/threadinitialize.c
+++ b/cpukit/score/src/threadinitialize.c
@@ -181,7 +181,10 @@ bool _Thread_Initialize(
   }
 
 #if defined(RTEMS_SMP)
+  the_thread->Scheduler.state = THREAD_SCHEDULER_BLOCKED;
+  the_thread->Scheduler.own_control = scheduler;
   the_thread->Scheduler.control = scheduler;
+  the_thread->Scheduler.own_node = the_thread->Scheduler.node;
   _Resource_Node_initialize( &the_thread->Resource_node );
   _CPU_Context_Set_is_executing( &the_thread->Registers, false );
 #endif