def acquire_read(self):
        """Acquire a read-lock. Blocks only if some thread has
        acquired write-lock."""
        self._read_ready.acquire()
        try:
            self._readers += 1
        finally:
            self._read_ready.release()
Acquire a read-lock. Blocks only if some thread has
        acquired write-lock.
recipes/Python/66426_ReadWriteLock/recipe-66426.py