threading

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counter = 0
lock = threading.RLock()

def func1():
  global counter

  while True:
    with lock:
      counter += 1
      counter -= 1

def func2():
  global counter

  while True:
    with lock:
      counter += 1
      counter -= 1

threading.Thrad(target=func1).start()
threading.Thrad(target=func2).start()

counter = 0

def func1():
  global counter

  while True:
    counter += 1
    counter -= 1

def func2():
  global counter

  while True:
    counter += 1
    counter -= 1

threading.Thrad(target=func1).start()
threading.Thrad(target=func2).start()