We don't need to any more presuming you get ideal remote cancellation
conditions where the remote actor should teardown and kill the streams
from its end.
On msg loop termination we now check and see if a channel is associated
with a child-actor registered in some local task's nursery. If so, we
attempt to wait on channel closure initiated from the child side (by
draining the underlying msg stream) so as to avoid closing it too early
resulting in the child not relaying its termination status response. This
means we now support the ideal case in 2-general's where we get back the
ack to the closure request instead of just ignoring it and timing out XD
The main implementation detail is that when `Portal.cancel_actor()`
remotely calls `Actor.cancel()` we actually wait for the RPC response
from that request before allowing the channel shutdown sequence to
engage. The new msg stream draining support enables this.
Also, factor child-to-parent error propagation logic into a helper func
and improve some docs (yeah yeah y'all don't like the ''', i don't
care - it makes my eyes not hurt).
Use a `trio.Event` to enable nursery closure detection such that core
runtime tasks can be notified when a local nursery exits and allow
shutdown protocols to operate without close-before-terminate issues
(such as IPC channel closure during remote peer cancellation).
Enables "draining" the last set of messages after a channel/stream has
been terminated mostly for the purposes of receiving a final ACK to
a remote cancel command. Also, add an internal `Channel._cancel_called`
flag which can be set by `Portal.cancel_actor()`.
It's definitely possible to have a nursery spawn task be cancelled
before a `trio.Process` handle is ever returned; we now handle this
case as a cancelled-during-spawn scenario. Zombie collection logic
also is bypassed in this case.
Currently if the spawn task is waiting on a daemon actor it is likely in
`await proc.wait()`, however, if the actor nursery is subsequently
cancelled this checkpoint will be abandoned and the hard proc reaping
sequence will execute which results in a up to 3 second wait before
a "hard" system signal is sent to the child. Ideally such
a cancelled-during-daemon-actor-wait condition is instead handled by
first trying to cancel the remote actor using `Portal.cancel_actor()` (a
"graceful" remote cancel request) which should (presuming normal runtime
operation) result in an immediate collection of the process after normal
actor (remotely triggered) runtime cancellation.
Thanks to @richardsheridan for pointing out the limitations of using
*any* kind of value as the result-cached-flag and how it might cause
problems for anyone returning pickled blob-data. This changes the
`Portal` internal result value tracking to stash the full message from
which the value can be retrieved by any `Portal.result()` caller.
The internal change is that `Portal._return_once()` now returns a tuple
of the message *and* its value.
Fixes the issue where if the main remote task returns `None`,
`Portal.result()` would erroneously wait again on the underlying feeder
mem chan since `None` was being used as the cache flag. Instead set the
flag as the channel uid and consider the result collected when set to
anything else (since it would be odd to return that value from a remote
task when you already can read it as part of portal/channel apis).
The api we've made here is actually closer to `asyncio.gather()` but
with opening async context managers instead of funcs. Use another event
to allow for graceful teardown of children on non-cancellation exits
and add a doc string.
Tyler Goodlet
goodboy
overclockworked64