Actor state via messages #190

goodboy · 2021-01-24T19:57:14Z

An example for @fjarri doing "actor state mutation via messages".

Feel free to criticize the heck out of it.

If you want to see how subactors could modify each other's state we can add that as well.

This is a draft of the `tractor` way to implement the example from the "processs pool" in the stdlib's `concurrent.futures` docs: https://docs.python.org/3/library/concurrent.futures.html#processpoolexecutor-example Our runtime is of course slower to startup but once up we of course get the same performance, this confirms that we need to focus some effort not on warm up and teardown times. The mp forkserver method definitely improves startup delay; rolling our own will likely be a good hot spot to play with. What's really nice is our implementation is done in approx 10th the code ;) Also, do we want offer and interface that yields results as they arrive? Relates to #175

goodboy · 2021-01-24T19:58:26Z

examples/actors/mutate_remote_state.py

+import trio
+import tractor
+
+_snd_chan, _recv_chan = trio.open_memory_channel(100)


sorry ignore this..
got left in from another idea.

goodboy · 2021-01-24T19:59:52Z

examples/actors/mutate_remote_state.py

+import tractor
+
+_snd_chan, _recv_chan = trio.open_memory_channel(100)
+_actor_state = {'some_state_stuff': None}


This is a module level variable meaning it maintains it's state for the entire process lifetime.
We could have just as easily made some function that "sleeps forever" and wakes up incrementally to report it's state if need be.

goodboy · 2021-01-24T20:20:41Z

examples/actors/mutate_remote_state.py

+
+
+@dataclass
+class MyProcessStateThing:


Instead of this what are you after?

A function that creates some object and then makes that object mutateable from another inbound message?

Maybe you want something like rays "actors" (which i would argue aren't really "actor model" actors):
https://docs.ray.io/en/latest/actors.html

We can also accomplish this but it will require a slight bit more machinery.

goodboy · 2021-01-25T01:43:22Z

How's that 2nd example @fjarri for a class / ray style actors api?

goodboy · 2021-01-26T12:45:00Z

examples/actors/ray_style_classes.py

+    # in a global var or are another clas scoped variable?
+    # If you want it somehow persisted in another namespace
+    # I'd be interested to know "where".
+    actor = ActorState()


I get this isn't ideal (though it really is no performance hit) in an idiomatic python sense, but the alternative is some other way to store this instance across function-task calls.

The normal way would be a module level variable (since they're "globally scoped") but I guess in theory you could have a function that stays alive and constantly passes the instance to other tasks over a memory channel - still in that case how does the new task get access to the channel handle?). The alternative is a module level class which has a class level variable which is again globally scoped on the class.

goodboy · 2021-01-26T13:19:10Z

examples/actors/ray_style_classes.py

+        )
+
+
+def get_method_proxy(portal, target=ActorState) -> MethodProxy:


In cases anyone gets cranky about this, from pykka docs:

The proxy object will use introspection to figure out what public attributes and methods the actor has, and then mirror the full API of the actor. Any attribute or method prefixed with underscore will be ignored, which is the convention for keeping stuff private in Python.

From https://www.pykka.org/en/latest/quickstart/#actor-proxies

fjarri · 2021-01-26T22:49:11Z

Sorry, there's been a lot of input from you in different channels, I'll summarize my thoughts here.

I'm afraid I still don't see the functionality (or even ways to implement the functionality) I need. When I think of an actor system, these are some of things I'm worried about:

how can a child send a message to its parent?
if a child wants to terminate or restart itself, how will the parent handle it?
how can I make message handlers async? How can I guarantee that as long as one message handler of an actor is running, another one will not be started?
how can I start a child in the same thread/other thread/other process with the same API, without changing the child's code?
how can I delay the message delivery?
how can I monitor the state of an actor from another actor (not necessarily the parent)?

I can see how my API (in https://gist.github.com/fjarri/803d2611fc8487c7853f17ed4ad1ec10) allows one to implement this functionality. The framework will have enough information to handle these problems. Right now tractor seems too low-level for all that. I will have no more help from it than I do from trio itself, except for more convenient multiprocessing.

goodboy · 2021-01-27T19:50:11Z

@fjarri thanks so much for the writeup 👍🏼.

I'll address these in order:

how can a child send a message to its paren

async with tractor.wait_for_actor('parent_name') as portal:
    ... do stuff with portal...

This is documented only very briefly. Note the "arbiter" stuff there is wrong and going away.

if a child wants to terminate or restart itself, how will the parent handle it?

However it wants to. Restarts are a naive basic operation the exact same as spawning or running a task through a portal. If you want a special error that the parent expects to handle then you can just raise it and expect it on the parent's side or you could just have the result of the remote task return a restart message of your choosing. I've pushed up an example showing both multiple task(s) restarts within a single subactor as well as restarts of multiple subactors entirely themselves:
https://github.com/goodboy/tractor/pull/190/files#diff-3d37ffe6c0c1d6567affe87d7c0edca4c18adb1d5735075084263351e1f642f8

To understand what's going more easily from a terminal you can run it with the following command:
$TERM -e watch -n 0.1 "pstree -a $$" & python examples/actors/most_basic_supervisor.py || kill $!

how can I start a child in the same thread/other thread/other process with the same API, without changing the child's code?

I honestly have no idea what you're asking here so you'll have to clarify. There is currently no hot-reloading of code support yet mostly because python doesn't have great facilities for this and thus it needs some thinking but we've had lots of discussion.

how can I delay the message delivery?

Again don't know what you mean. If you want a reactive style delay there are already trio libs underway supporting this.

how can I monitor the state of an actor from another actor (not necessarily the parent)?

As per the 1st bullet, contact the actor by name, get a portal, send it a message, get a response.
There is no built-in "monitoring" system on purpose for now.

goodboy · 2021-01-27T20:04:53Z

examples/actors/most_basic_supervisor.py

+        # We'll show both.
+
+        async with trio.open_nursery() as n:
+            # we'll doe the first as a lone task restart in a daemon actor


brutal typo

it's clearly 3 tasks that are constantly restarted...

goodboy · 2021-01-27T20:05:41Z

examples/actors/most_basic_supervisor.py

+            for i in range(4):
+                n.start_soon(respawn_remote_task, p0)
+
+            # Open another nursery that will respawn sub-actors


nope x this. no extra nursery required.. originally it had that but we don't need it.

goodboy · 2021-01-27T20:06:33Z

examples/actors/most_basic_supervisor.py

+            # Open another nursery that will respawn sub-actors
+
+            # spawn a set of subactors that will signal restart
+            # of the group of processes on each failures


still need to add a loop around the nursery to restart everything if we get a certain error raised. this starts getting into a more formal supervisor strategy api that we have yet to design.

hmm actualy just had the idea of doing something like:

async with tractor.supervise_with('one_for_one') as srat: async with tractor.open_nursery() as tn: .. do tractor stuff

@guilledk @salotz thots?

hmm we might have to plug into the nursery internals a bit more to get granular control on each sub-proc. needs a little more pondering fo sho.

oh and common strat names from erlang:
https://learnyousomeerlang.com/supervisors

actually i guess you'd want to pass the nursery into the strat so that you get the granular control.. hmm that might compose nicely actually. Then in theory you could use a stack to compose multiple strats?

Woo this actually will be interesting i'm thinking.

goodboy · 2021-05-17T14:14:02Z

FYI we can probably vastly improve the example "proxy" code here with the new native bidir streaming support in #209 🏄🏼

goodboy added 12 commits January 24, 2021 14:53

Make new paralellism example space

da27d96

Remove use of tractor.run()

f715a0c

Yield results on demand using a mem chan

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More comments

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Add concise readme example

582eda4

Contain the error

47651ea

Run parallel examples

5db737d

Add aclosing() around asyn gen loop

2ed071c

Ignore type checks on stdlib overrides

5da86a0

Fix more stdlib typing issues with latest mypy

ce61230

Add an actor "state mutation" via messages example

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goodboy force-pushed the eg_worker_poolz branch from c0dbcc5 to ce61230 Compare January 24, 2021 19:57

goodboy commented Jan 24, 2021

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Use a global dataclass instead, cuz we like "objects"?

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Add class style "actors" example with client proxy API

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goodboy commented Jan 26, 2021

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goodboy mentioned this pull request Jan 26, 2021

Recipe for "actor class" style stuff like ray and pykka #191

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goodboy added 2 commits January 27, 2021 14:40

Add a super basic supervisor/restart example

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goodboy force-pushed the eg_worker_poolz branch from ce61230 to 5ffd2d2 Compare February 21, 2021 19:08

Base automatically changed from eg_worker_poolz to master February 22, 2021 14:55

goodboy mentioned this pull request Mar 4, 2021

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Actor state via messages #190

Actor state via messages #190

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goodboy commented May 17, 2021

		)


		def get_method_proxy(portal, target=ActorState) -> MethodProxy:

Actor state via messages #190

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Actor state via messages #190

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