Add full support for using the "spawn" process starting method as per:
https://docs.python.org/3/library/multiprocessing.html#contexts-and-start-methods
Add a `spawn_method` argument to `tractor.run()` for specifying the
desired method explicitly. By default use the "fastest" method available.
On *nix systems this is the original "forkserver" method.
This should be the solution to getting windows support!
Resolves#60
As mentioned in prior commits there's currently a bug in Python that
make async gens **not** task safe. Since this is the core cause of almost
all recent problems, instead implement our own async iterator derivative of
`trio.abc.ReceiveChannel` by wrapping a `trio._channel.MemoryReceiveChannel`.
This fits more natively with the memory channel API in ``trio`` and adds
potentially more flexibility for possible bidirectional inter-actor streaming
in the future.
Huge thanks to @oremanj and of course @njsmith for guidance on this one!
In combination with `.aclose()`-ing the async gen instance returned from
`Portal.run()` this demonstrates the python bug:
https://bugs.python.org/issue32526
I've commented out the line that triggers the bug for now since this
case provides motivation for adding our own `trio.abc.ReceiveMemoryChannel`
implementation to be used instead of async gens directly (returned from
`Portal.run()`) since the latter is **not** task safe.
For now stop `.aclose()`-ing all async gens on portal close since it can
cause hangs and other weird behaviour if another task operates on the
same instance.
See https://bugs.python.org/issue32526.
Use an inner function / closure to properly process required arguments
at call time as is recommended in the `wrap` docs. Do async gen and
arg introspection at decorate time and raise appropriate type errors.
Turns out you get a bad situation if the target actor who's task you're
trying to cancel has already died (eg. from an external
`KeyboardInterrupt` or other error) and so we need to eventually bail on
the RPC request. Also don't bother closing the channel created in
`open_portal()` manually since the cancel scope should take care of all
that.
- when calling the async gen func provided by the user wrap it in
`@async_generator.aclosing` to ensure correct teardown at cancel time
- expect the gen to yield a dict with topic keys and data values
- add a `packetizer` function argument to the api allowing a user
to format the data to be published in whatever way desired
- support using the decorator without the parentheses (using default
arguments)
- use a `wrapt` "adapter" to override the signature presented to the
`_actor._invoke` inspection machinery
- handle the default case where `tasks` isn't provided; allow only one
concurrent publisher task
- store task locks in an actor local variable
- add a comprehensive doc string
Use the new `Actor.cancel_task()` api to remotely cancel streaming
tasks spawned by a portal. This guarantees that if an actor is
cancelled all its (remote) portal spawned tasks will be as well.
On portal teardown only cancel all async
generator calls (though we should cancel all RPC requests in general
eventually) and don't close the channel since it may have been passed
in from some other context that wishes to keep it connected. In
`open_portal()` run the message loop shielded so that if the local
task is cancelled, messaging will continue until the internal scope
is cancelled at end of block.
Christian López Barrón
Tyler Goodlet
tgoodlet