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, 2 insertions, 0 deletions

diff --git a/cpukit/score/src/scheduleredfnodeinit.c b/cpukit/score/src/scheduleredfnodeinit.c
index b23f5acda8..e7f8af70a5 100644
--- a/cpukit/score/src/scheduleredfnodeinit.c
+++ b/cpukit/score/src/scheduleredfnodeinit.c
@@ -29,6 +29,8 @@ void _Scheduler_EDF_Node_initialize(
 
   (void) scheduler;
 
+  _Scheduler_Node_do_initialize( &node->Base, the_thread );
+
   node->thread = the_thread;
   node->queue_state = SCHEDULER_EDF_QUEUE_STATE_NEVER_HAS_BEEN;
 }