Source code for kazoo.recipe.counter

"""Zookeeper Counter

:Maintainer: None
:Status: Unknown


from kazoo.exceptions import BadVersionError
from kazoo.retry import ForceRetryError

[docs]class Counter(object): """Kazoo Counter A shared counter of either int or float values. Changes to the counter are done atomically. The general retry policy is used to retry operations if concurrent changes are detected. The data is marshaled using `repr(value)` and converted back using `type(counter.default)(value)` both using an ascii encoding. As such other data types might be used for the counter value. Counter changes can raise :class:`~kazoo.exceptions.BadVersionError` if the retry policy wasn't able to apply a change. Example usage: .. code-block:: python zk = KazooClient() counter = zk.Counter("/int") counter += 2 counter -= 1 counter.value == 1 counter = zk.Counter("/float", default=1.0) counter += 2.0 counter.value == 3.0 """
[docs] def __init__(self, client, path, default=0): """Create a Kazoo Counter :param client: A :class:`~kazoo.client.KazooClient` instance. :param path: The counter path to use. :param default: The default value. """ self.client = client self.path = path self.default = default self.default_type = type(default) self._ensured_path = False
def _ensure_node(self): if not self._ensured_path: # make sure our node exists self.client.ensure_path(self.path) self._ensured_path = True def _value(self): self._ensure_node() old, stat = self.client.get(self.path) old = old.decode('ascii') if old != b'' else self.default version = stat.version data = self.default_type(old) return data, version @property def value(self): return self._value()[0] def _change(self, value): if not isinstance(value, self.default_type): raise TypeError('invalid type for value change') self.client.retry(self._inner_change, value) return self def _inner_change(self, value): data, version = self._value() data = repr(data + value).encode('ascii') try: self.client.set(self.path, data, version=version) except BadVersionError: # pragma: nocover raise ForceRetryError()
[docs] def __add__(self, value): """Add value to counter.""" return self._change(value)
[docs] def __sub__(self, value): """Subtract value from counter.""" return self._change(-value)