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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _harvest_lost_resources(self):
 """Return lost resources to pool."""

        with self._lock:
            for i in self._unavailable_range():
                rtracker = self._reference_queue[i]
                if rtracker is not None and rtracker.available():
                    self.put_resource(rtracker.resource)