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The thread priority is manifest in two independent areas. One area is the user visible thread priority along with a potential thread queue. The other is the scheduler. Currently, a thread priority update via _Thread_Change_priority() first updates the user visble thread priority and the thread queue, then the scheduler is notified if necessary. The priority is passed to the scheduler via a local variable. A generation counter ensures that the scheduler discards out-of-date priorities. This use of a local variable ties the update in these two areas close together. For later enhancements and the OMIP locking protocol implementation we need more flexibility. Add a thread priority information block to Scheduler_Node and synchronize priority value updates via a sequence lock on SMP configurations. Update #2556.