Add `Actor._cancel_called` and `._cancel_complete` making it possible to
determine whether the actor has started the cancellation sequence and
whether that sequence has fully completed. This allows for blocking in
internal machinery tasks as necessary. Also, always trigger the end of
ongoing rpc tasks even if the last task errors; there's no guarantee the
trio cancellation semantics will guarantee us a nice internal "state"
without this.
For reliable remote cancellation we need to "report" `trio.Cancelled`s
(just like any other error) when exhausting a portal such that the
caller can make decisions about cancelling the respective actor if need
be.
Resolves#156
This appears to demonstrate the same bug found in #156. It looks like
cancelling a subactor with a child, while that child is running sync code,
can result in the child never getting cancelled due to some strange
condition where the internal nurseries aren't being torn down as
expected when a `trio.Cancelled` is raised.
Every subactor in the tree now receives the socket (or whatever the
mailbox type ends up being) during startup and can call the new
`tractor._discovery.get_root()` function to get a portal to the current
root actor in their tree. The main reason for adding this atm is to
support nested child actors gaining access to the root's tty lock for
debugging.
Also, when a channel disconnects from a message loop, might as well kill
all its rpc tasks.
It's not like any of this code is really being used anyway since we
aren't indefinitely blocking for cancelled subactors to terminate (yet).
Drop the `do_hard_kill()` bit for now and just rely on the underlying
process api. Oh, and mark the nursery as cancelled asap.
Seems like the request task cancel scope is actually solving all the
deadlock issues and masking SIGINT isn't changing much behaviour at all.
I think let's keep it unmasked for now in case it does turn out useful
in cancelling from unrecoverable states while in debug.
This is needed in order to avoid the deadlock condition where
a child actor is waiting on the root actor's tty lock but it's parent
(possibly the root) is waiting on it to terminate after sending a cancel
request. The solution is simple: create a cancel scope around the
request in the child and always cancel it when a cancel request from the
parent arrives.
There seems to be no good reason not too since our cancellation
machinery/protocol should do this work when the root receives the
signal. This also (hopefully) helps with some debugging race condition
stuff.
This seems to prevent a certain class of bugs to do with the root actor
cancelling local tasks and getting into deadlock while children are
trying to acquire the tty lock. I'm not sure it's the best idea yet
since you're pretty much guaranteed to get "stuck" if a child activates
the debugger after the root has been cancelled (at least "stuck" in
terms of SIGINT being ignored). That kinda race condition seems to still
exist somehow: a child can "beat" the root to activating the tty lock
and the parent is stuck waiting on the child to terminate via its
nursery.
This aids with tearing down resources **after** the crash handling and
debugger have completed. Leaving this internal for now but should
eventually get a public convenience function like
`tractor.context_stack()`.
Keep an actor local (bool) flag which determines if there is already
a running debugger instance for the current process. If another task
tries to enter in this case, simply ignore it since allowing entry may
result in a deadlock where the new task will be sync waiting on the
parent stdio lock (a case that will never arrive due to the current
debugger's active use of it).
In the future we may want to allow FIFO queueing of local tasks where
instead of ignoring re-entrant breakpoints we allow tasks to async wait
for debugger release, though not sure the implications of that since
you'd likely want to support switching the debugger to the new task and
that could cause deadlocks where tasks are inter-dependent. It may be
more sane to just error on multiple breakpoint requests within an actor.
This is the first step in addressing #113 and the initial support
of #130. Basically this allows (sub)processes to engage the `pdbpp`
debug machinery which read/writes the root actor's tty but only in
a FIFO semaphored way such that no two processes are using it
simultaneously. That means you can have multiple actors enter a trace or
crash and run the debugger in a sensible way without clobbering each
other's access to stdio. It required adding some "tear down hooks" to
a custom `pdbpp.Pdb` type such that we release a child's lock on the
parent on debugger exit (in this case when either of the "continue" or
"quit" commands are issued to the debugger console).
There's some code left commented in anticipation of full support for
issue #130 where we're need to actually capture and feed stdin to the
target (remote) actor which won't necessarily being running on the same
host.
Tyler Goodlet
goodboy