magic-wormhole/src/wormhole/journal.py

from __future__ import print_function, absolute_import, unicode_literals
from zope.interface import implementer
import contextlib
from ._interfaces import IJournal

@implementer(IJournal)
class Journal(object):
    def __init__(self, save_checkpoint):
        self._save_checkpoint = save_checkpoint
        self._outbound_queue = []
        self._processing = False

    def queue_outbound(self, fn, *args, **kwargs):
        assert self._processing
        self._outbound_queue.append((fn, args, kwargs))

    @contextlib.contextmanager
    def process(self):
        assert not self._processing
        assert not self._outbound_queue
        self._processing = True
        yield # process inbound messages, change state, queue outbound
        self._save_checkpoint()
        for (fn, args, kwargs) in self._outbound_queue:
            fn(*args, **kwargs)
        self._outbound_queue[:] = []
        self._processing = False


@implementer(IJournal)
class ImmediateJournal(object):
    def __init__(self):
        pass
    def queue_outbound(self, fn, *args, **kwargs):
        fn(*args, **kwargs)
    @contextlib.contextmanager
    def process(self):
        yield