class_docstr: A simple reader-writer lock Several readers can hold the lock
  simultaneously, XOR one writer. Write locks have priority over reads to
  prevent write starvation.
class_docstr_tok: ["A","simple","reader-writer","lock","Several","readers","can","hold","the","lock","simultaneously",",","XOR","one","writer",".","Write","locks","have","priority","over","reads","to","prevent","write","starvation","."]
code: def __init__(self):
      self.rwlock = 0
      self.writers_waiting = 0
      self.monitor = threading.Lock()
      self.readers_ok = threading.Condition(self.monitor)
      self.writers_ok = threading.Condition(self.monitor)
  
imports: import threading
label_desc: Use image node_id 1 to create a new RWLock object  with example: obj = RWLock()