commit ef06783b96ee38230b41cc08c14032d7127f867b Author: Damian Johnson atagar@torproject.org Date: Tue Jul 7 16:03:11 2020 -0700

Investigate an async ainit method

Our ainit method should be asynchronous, but guess that's not to be. Documenting the issues we encountered. --- stem/util/__init__.py | 52 +++++++++++++++++++++++++++++++++++++++++++-------- 1 file changed, 44 insertions(+), 8 deletions(-)

diff --git a/stem/util/__init__.py b/stem/util/__init__.py index 5a8f95e0..cddce755 100644 --- a/stem/util/__init__.py +++ b/stem/util/__init__.py @@ -199,14 +199,11 @@ class Synchronous(object): """

def __init__(self) -> None: - ainit_func = getattr(self, '__ainit__', None) - if Synchronous.is_asyncio_context(): self._loop = asyncio.get_running_loop() self._loop_thread = None

- if ainit_func: - ainit_func() + self.__ainit__() else: self._loop = asyncio.new_event_loop() self._loop_thread = threading.Thread( @@ -231,11 +228,50 @@ class Synchronous(object): if inspect.iscoroutinefunction(func): setattr(self, method_name, functools.partial(call_async, func))

- if ainit_func: - async def call_ainit(): - ainit_func() + asyncio.run_coroutine_threadsafe(asyncio.coroutine(self.__ainit__)(), self._loop).result() + + def __ainit__(self): + """ + Implicitly called during construction. This method is assured to have an + asyncio loop during its execution. + """

- asyncio.run_coroutine_threadsafe(call_ainit(), self._loop).result() + # This method should be async (so 'await' works), but apparently that + # is not possible. + # + # When our object is constructed our __init__() can be called from a + # synchronous or asynchronous context. If synchronous, it's trivial to + # run an asynchronous variant of this method because we fully control + # the execution of our loop... + # + # asyncio.run_coroutine_threadsafe(self.__ainit__(), self._loop).result() + # + # However, when constructed from an asynchronous context the above will + # likely hang because our loop is already processing a task (namely, + # whatever is constructing us). While we can schedule tasks, we cannot + # invoke it during our construction. + # + # Finally, when this method is simple we could directly invoke it... + # + # class Synchronous(object): + # def __init__(self): + # if Synchronous.is_asyncio_context(): + # try: + # self.__ainit__().send(None) + # except StopIteration: + # pass + # else: + # asyncio.run_coroutine_threadsafe(self.__ainit__(), self._loop).result() + # + # async def __ainit__(self): + # # asynchronous construction + # + # However, this breaks if any 'await' suspends our execution. For more + # information see... + # + # https://stackoverflow.com/questions/52783605/how-to-run-a-coroutine-outside-... + + pass

def close(self) -> None: """