This mostly adds the api described in
https://github.com/goodboy/tractor/issues/53#issuecomment-806258798
The first draft summary:
- formalize bidir steaming using the `trio.Channel` style interface
which we derive as a `MsgStream` type.
- add `Portal.open_context()` which provides a `trio.Nursery.start()`
remote task invocation style for setting up and tearing down tasks
contexts in remote actors.
- add a distinct `'started'` message to the ipc protocol to facilitate
`Context.start()` with a first return value.
- for our `ReceiveMsgStream` type, don't cancel the remote task in
`.aclose()`; this is now done explicitly by the surrounding `Context`
usage: `Context.cancel()`.
- streams in either direction still use a `'yield'` message keeping the
proto mostly symmetric without having to worry about which side is the
caller / portal opener.
- subtlety: only allow sending a `'stop'` message during a 2-way
streaming context from `ReceiveStream.aclose()`, detailed comment
with explanation is included.
Relates to #53
NB: this is a breaking change removing support for `Portal.run()` being
able to invoke remote streaming functions and instead replacing the
method call with an async context manager api `Portal.open_stream_from()`
This style explicitly defines stream teardown at the call site instead
of expecting the user to handle tricky things correctly themselves: eg.
`async_geneartor.aclosing()`. Going forward `Portal.run()` can be used
only for invoking async functions.
Move receive stream into streaming modules and rebrand as a "message
stream". Factor out cancellation mechanics in `.aclose()` into the
`Context` type which will soon provide the api for for cancelling portal
invocations. Comment-stage a few methods on both types in anticipation
of a new bi-directional streaming api. Add a `MsgStream` bidirectional
channel type which will be the eventual type yielded from
`Context.open_stream()`. Adjust the response/dialog types to be the set
`{'asyncfun', 'asyncgen', 'context'}`. OH, and add async func checking
in `Portal.run()` to catch and error on sync funcs early.
It turns out in order to maintain our sneaky little "call an `Actor`
method in this remote process" we still need the ability to invoke
functions from a namespace. We're currently using a "self" namespace as
a way to do this for internal inter-process method calling. Either way,
I see no reason not to keep a public method for this invoke style (we
just won't market it) since it is still how the machinery works
underneath.
This resolves and completes #69 allowing all RPC invocation APIs to pass
function references directly instead of explicit `str` names for the
target namespace and function (this is still done implicitly
underneath). This brings us closer to `trio`'s task running API as well
as acknowledges that any inter-host RPC system (and API) will likely
need to be implemented on top of local RPC primitives anyway. Even if
this ends up **not** being true we can always go to "function stubs" as
part of our IAC protocol or, add a new method to do explicit namespace
calls: `.run_from_module()` or whatever everyone votes on.
Resolves#69
Further, this commit drops `Actor.statespace` from the entire system
since a user can easily get this same functionality using module
level variables. Fix docs to match all these changes (luckily mostly
already done due to example scripts referencing).
Add a ``tractor._portal.StreamReceiveChannel.shield_channel()`` context
manager which allows for avoiding the closing of an IPC stream's
underlying channel for the purposes of task re-spawning. Sometimes you
might want to cancel a task consuming a stream but not tear down the IPC
between actors (the default). A common use can might be where the task's
"setup" work might need to be redone but you want to keep the
established portal / channel in tact despite the task restart.
Includes a test.
This begins moving toward explicitly decorated "streaming functions"
instead of checking for a `ctx` arg in the signature.
- provide each context with its task's top level `trio.CancelScope`
such that tasks can cancel themselves explictly if needed via calling
`Context.cancel_scope()`
- make `Actor.cancel_task()` a private method (`_cancel_task()`) and
handle remote rpc calls specially such that the caller does not need
to provide the `chan` argument; non-primitive types can't be passed on
the wire and we don't want the client actor be require knowledge of
the channel instance the request is associated with. This also ties into
how we're tracking tasks right now (`Actor._rpc_tasks` is keyed by the
call id, a UUID, *plus* the channel).
- make `_do_handshake` a private actor method
- use UUID version 4
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!
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.
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.
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.
Use the new custom error types throughout the actor and portal
primitives and set a few new rules:
- internal errors are any error not raised by an rpc task and are
**not** forwarded to portals but instead are raised directly in
the msg loop.
- portals always re-raise a "main task" error for every call to
``Portal.result()``.
This is purely for documentation purposes for now as it should be
obvious a bunch of the signatures aren't using the correct "generics"
syntax (i.e. the use of `(str, int)` instead of `typing.Tuple[str, int])`)
in a bunch of places. We're also not using a type checker yet and besides,
`trio` doesn't really expose a lot of its internal types very well.
2SQASH
This ensures that internal errors received from a remote actor are
indeed raised even in the `MainProcess` **before** comms tasks are
cancelled. Internal error in this case means any error packet received
on a channel that doesn't have a `cid` header. RPC errors (which **do**
have a `cid` header) are still forwarded to the consuming caller as usual.
Start a forkserver once in the main (parent-most) process
and pass ipc info (fds) to subprocesses manually such that embedded
calls to `multiprocessing.Process.start()` just work. Note that this
relies on our overridden version of the stdlib's
`multiprocessing.forkserver` module.
Resolves#6
Stop worrying about a "main task" in each actor and instead add an
additional `ActorNursery.run_in_actor()` method which wraps calls
to create an actor and run a lone RPC task inside it. Note this
adjusts the public API of `ActorNursery.start_actor()` to drop
its `main` kwarg.
The dirty deats of making this possible:
- each spawned RPC task is now tracked with a specific cancel scope such
that when the actor is cancelled all ongoing responders are cancelled
before any IPC/channel machinery is closed (turns out that spawning
new actors from `outlive_main=True` actors was probably borked before
finally getting this working).
- make each initial RPC response be a packet which describes the
`functype` (eg. `{'functype': 'asyncfunction'}`) allowing for async
calls/submissions by client actors (this was required to make
`run_in_actor()` work - `Portal._submit()` is the new async method).
- hooray we can stop faking "main task" results for daemon actors
- add better handling/raising of internal errors caught in the bowels of
the `Actor` itself.
- drop the rpc spawning nursery; just use the `Actor._root_nursery`
- only wait on `_no_more_peers` if there are existing peer channels that
are actually still connected.
- an `ActorNursery.__aexit__()` now implicitly waits on `Portal.result()` on close
for each `run_in_actor()` spawned actor.
- handle cancelling partial started actors which haven't yet connected
back to the parent
Resolves#24
Tyler Goodlet
Tyler Goodlet