tractor/NEWS.rst

Changelog

tractor 0.1.0a4 (2021-12-17)

Features

• #275: Re-license code base under AGPLv3. Also see #274 for majority contributor consensus on this decision.

• #121: Add "infected asyncio mode; a sub-system to spawn and control asyncio actors using trio's guest-mode.

  This gets us the following very interesting functionality:

  • ability to spawn an actor that has a process entry point of asyncio.run() by passing infect_asyncio=True to Portal.start_actor() (and friends).
  • the asyncio actor embeds trio using guest-mode and starts a main trio task which runs the tractor.Actor._async_main() entry point engages all the normal tractor runtime IPC/messaging machinery; for all purposes the actor is now running normally on a trio.run().
  • the actor can now make one-to-one task spawning requests to the underlying asyncio event loop using either of:
    • to_asyncio.run_task() to spawn and run an asyncio task to completion and block until a return value is delivered.
    • async with to_asyncio.open_channel_from(): which spawns a task and hands it a pair of "memory channels" to allow for bi-directional streaming between the now SC-linked trio and asyncio tasks.

  The output from any call(s) to asyncio can be handled as normal in trio/tractor task operation with the caveat of the overhead due to guest-mode use.

  For more details see the original PR and issue.

• #257: Add trionics.maybe_open_context() an actor-scoped async multi-task context manager resource caching API.

  Adds an SC-safe cacheing async context manager api that only enters on the first task entry and only exits on the last task exit while in between delivering the same cached value per input key. Keys can be either an explicit key named arg provided by the user or a hashable kwargs dict (will be converted to a list[tuple]) which is passed to the underlying manager function as input.

• #261: Add cross-actor-task Context oriented error relay, a new stream overrun error-signal StreamOverrun, and support disabling MsgStream backpressure as the default before a stream is opened or by choice of the user.

  We added stricter semantics around tractor.Context.open_stream(): particularly to do with streams which are only opened at one end. Previously, if only one end opened a stream there was no way for that sender to know if msgs are being received until first, the feeder mem chan on the receiver side hit a backpressure state and then that condition delayed its msg loop processing task to eventually create backpressure on the associated IPC transport. This is non-ideal in the case where the receiver side never opened a stream by mistake since it results in silent block of the sender and no adherence to the underlying mem chan buffer size settings (which is still unsolved btw).

  To solve this we add non-backpressure style message pushing inside Actor._push_result() by default and only use the backpressure trio.MemorySendChannel.send() call iff the local end of the context has entered Context.open_stream():. This way if the stream was never opened but the mem chan is overrun, we relay back to the sender a (new exception) SteamOverrun error which is raised in the sender's scope with a special error message about the stream never having been opened. Further, this behaviour (non-backpressure style where senders can expect an error on overruns) can now be enabled with .open_stream(backpressure=False) and the underlying mem chan size can be specified with a kwarg msg_buffer_size: int.

  Further bug fixes and enhancements in this changeset include:

  • fix a race we were ignoring where if the callee task opened a context it could enter Context.open_stream() before calling .started().
  • Disallow calling Context.started() more then once.
  • Enable Context linked tasks error relaying via the new Context._maybe_raise_from_remote_msg() which (for now) uses a simple trio.Nursery.start_soon() to raise the error via closure in the local scope.

• #267: This (finally) adds fully acknowledged remote cancellation messaging support for both explicit Portal.cancel_actor() calls as well as when there is a "runtime-wide" cancellations (eg. during KBI or general actor nursery exception handling which causes a full actor "crash"/termination).

  You can think of this as the most ideal case in 2-generals where the actor requesting the cancel of its child is able to always receive back the ACK to that request. This leads to a more deterministic shutdown of the child where the parent is able to wait for the child to fully respond to the request. On a localhost setup, where the parent can monitor the state of the child through process or other OS APIs instead of solely through IPC messaging, the parent can know whether or not the child decided to cancel with more certainty. In the case of separate hosts, we still rely on a simple timeout approach until such a time where we prefer to get "fancier".

• #271: Add a per actor debug_mode: bool control to our nursery.

  This allows spawning actors via ActorNursery.start_actor() (and other dependent methods) with a debug_mode=True flag much like tractor.open_nursery(): such that per process crash handling can be toggled for cases where a user does not need/want all child actors to drop into the debugger on error. This is often useful when you have actor-tasks which are expected to error often (and be re-run) but want to specifically interact with some (problematic) child.

Bugfixes

• #239: Fix keyboard interrupt handling in Portal.open_context() blocks.

  Previously this not triggering cancellation of the remote task context and could result in hangs if a stream was also opened. This fix is to accept BaseException since it is likely any other top level exception other then kbi (even though not expected) should also get this result.

• #264: Fix Portal.run_in_actor() returns None result.

  None was being used as the cached result flag and obviously breaks on a None returned from the remote target task. This would cause an infinite hang if user code ever called Portal.result() before the nursery exit. The simple fix is to use the return message as the initial "no-result-received-yet" flag value and, once received, the return value is read from the message to avoid the cache logic error.

• #266: Fix graceful cancellation of daemon actors

  Previously, his was a bug where if the soft wait on a sub-process (the await .proc.wait()) in the reaper task teardown was cancelled we would fail over to the hard reaping sequence (meant for culling off any potential zombies via system kill signals). The hard reap has a timeout of 3s (currently though in theory we could make it shorter?) before system signalling kicks in. This means that any daemon actor still running during nursery exit would get hard reaped (3s later) instead of cancelled via IPC message. Now we catch the trio.Cancelled, call Portal.cancel_actor() on the daemon and expect the child to self-terminate after the runtime cancels and shuts down the process.

• #278: Repair inter-actor stream closure semantics to work correctly with tractor.trionics.BroadcastReceiver task fan out usage.

  A set of previously unknown bugs discovered in 257 let graceful stream closure result in hanging consumer tasks that use the broadcast APIs. This adds better internal closure state tracking to the broadcast receiver and message stream APIs and in particular ensures that when an underlying stream/receive-channel (a broadcast receiver is receiving from) is closed, all consumer tasks waiting on that underlying channel are woken so they can receive the trio.EndOfChannel signal and promptly terminate.

tractor 0.1.0a3 (2021-11-02)

Features

• Switch to using the trio process spawner by default on windows. (#166)

  This gets windows users debugger support (manually tested) and in general a more resilient (nested) actor tree implementation.

• Add optional msgspec support as an alernative, faster MessagePack codec. (#214)

  Provides us with a path toward supporting typed IPC message contracts. Further, msgspec structs may be a valid tool to start for formalizing our "SC dialog un-protocol" messages as described in #36`.

• Introduce a new tractor.trionics sub-package that exposes a selection of our relevant high(er) level trio primitives and goodies. (#241)

  At outset we offer a gather_contexts() context manager for concurrently entering a sequence of async context managers (much like a version of asyncio.gather() but for context managers) and use it in a new tractor.open_actor_cluster() manager-helper that can be entered to concurrently spawn a flat actor pool. We also now publicly expose our "broadcast channel" APIs (open_broadcast_receiver()) from here.

• Change the core message loop to handle task and actor-runtime cancel requests immediately instead of scheduling them as is done for rpc-task requests. (#245)

  In order to obtain more reliable teardown mechanics for (complex) actor trees it's important that we specially treat cancel requests as having higher priority. Previously, it was possible that task cancel requests could actually also themselves be cancelled if a "actor-runtime" cancel request was received (can happen during messy multi actor crashes that propagate). Instead cancels now block the msg loop until serviced and a response is relayed back to the requester. This also allows for improved debugger support since we have determinism guarantees about which processes must wait before hard killing their children.

• Drop Python 3.8 support in favor of rolling with two latest releases for the time being. (#248)

Misc

• #243 add a discint 'CANCEL' log level to allow the runtime to emit details about cancellation machinery statuses.

tractor 0.1.0a2 (2021-09-07)

Features

• Add tokio-style broadcast channels as a solution for #204 and discussed thoroughly in trio/#987.

  This gives us local task broadcast functionality using a new BroadcastReceiver type which can wrap trio.ReceiveChannel and provide fan-out copies of a stream of data to every subscribed consumer. We use this new machinery to provide a ReceiveMsgStream.subscribe() async context manager which can be used by actor-local concumers tasks to easily pull from a shared and dynamic IPC stream. (#229)

Bugfixes

• Handle broken channel/stream faults where the root's tty lock is left acquired by some child actor who went MIA and the root ends up hanging indefinitely. (#234)

  There's two parts here: we no longer shield wait on the lock and, now always do our best to release the lock on the expected worst case connection faults.

Deprecations and Removals

• Drop stream "shielding" support which was originally added to sidestep a cancelled call to .receive()

  In the original api design a stream instance was returned directly from a call to Portal.run() and thus there was no "exit phase" to handle cancellations and errors which would trigger implicit closure. Now that we have said enter/exit semantics with Portal.open_stream_from() and Context.open_stream() we can drop this implicit (and arguably confusing) behavior. (#230)

• Drop Python 3.7 support in preparation for supporting 3.9+ syntax. (#232)

tractor 0.1.0a1 (2021-08-01)

Features

• Updated our uni-directional streaming API (#206) to require a context manager style async with Portal.open_stream_from(target) as stream: which explicitly determines when to stop a stream in the calling (aka portal opening) actor much like async_generator.aclosing() enforcement.
• Improved the multiprocessing backend sub-actor reaping (#208) during actor nursery exit, particularly during cancellation scenarios that previously might result in hard to debug hangs.
• Added initial bi-directional streaming support in #219 with follow up debugger improvements via #220 using the new tractor.Context cross-actor task syncing system. The debugger upgrades add an edge triggered last-in-tty-lock semaphore which allows the root process for a tree to avoid clobbering children who have queued to acquire the pdb repl by waiting to cancel sub-actors until the lock is known to be released and has no pending waiters.

Experiments and WIPs

• Initial optional msgspec serialization support in #214 which should hopefully land by next release.
• Improved "infect asyncio" cross-loop task cancellation and error propagation by vastly simplifying the cross-loop-task streaming approach. We may end up just going with a use of anyio in the medium term to avoid re-doing work done by their cross-event-loop portals. See the infect_asyncio for details.

Improved Documentation

• Updated our readme to include more (and better) examples (with matching multi-terminal process monitoring shell commands) as well as added many more examples to the repo set.
• Added a readme "actors under the hood" section in an effort to guard against suggestions for changing the API away from trio's tasks-as-functions style.
• Moved to using the sphinx book theme though it needs some heavy tweaking and doesn't seem to show our logo on rtd :(

Trivial/Internal Changes

• Added a new TransportClosed internal exception/signal (#215 for catching TCP channel gentle closes instead of silently falling through the message handler loop via an async generator return.

Deprecations and Removals

• Dropped support for invoking sync functions (#205) in other actors/processes since you can always wrap a sync function from an async one. Users can instead consider using trio-parallel which is a project specifically geared for purely synchronous calls in sub-processes.
• Deprecated our tractor.run() entrypoint #197; the runtime is now either started implicitly in first actor nursery use or via an explicit call to tractor.open_root_actor(). Full removal of tractor.run() will come by beta release.

tractor 0.1.0a0 (2021-02-28)

Summary

• trio based process spawner (using subprocess)
• initial multi-process debugging with pdb++
• windows support using both trio and multiprocessing spawners
• "portal" api for cross-process, structured concurrent, (streaming) IPC