My information about locking and scheduling is dated and naiive. What is preventing per-thread structure of two identifiers "I am waiting for thing X, give it p

My information about locking and scheduling is dated and naiive. What is preventing per-thread structure of two identifiers "I am waiting for thing X, give it priority" and "I am in posession of X"? Identifiers are random numbers. System call is not necessary, some writable location is enough.