renewable-resource.py

# https://gitter.im/python-trio/general?at=5c6f46089155d45d905346b3

import trio
from functools import partial

class RenewableResource(trio.abc.AsyncResource):
    def __init__(self, factory, *args):
        self._factory = partial(factory, *args)
        self._resource = None

    @asynccontextmanager
    async def use(self):
        if self._resource is None:
            self._resource = await self._factory()
        try:
            yield self._resource
        except:
            await self.aclose()
            raise

    async def aclose(self):
        if self._resource is not None:
            resource = self._resource
            self._resource = None
            await resource.aclose()



# This with block controls the lifetime of abstract "renewable resource", and
# makes sure that the final concrete resource eventually gets closed
async with RenewableResource(partial(open_websocket, ...)) as resource:
    # Each time we 'async with use' it, it re-uses the last one if possible,
    # otherwise recreates it
    async with resource.use() as ws:
        # Use the websocket here
        ...