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syndicate-rs/syndicate/src/actor.rs

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#![doc = concat!(
include_str!("../doc/actor.md"),
include_str!("../doc/what-is-an-actor.md"),
include_str!("../doc/flow-control.md"),
include_str!("../doc/linked-tasks.md"),
)]
use super::schemas::sturdy;
use super::error::Error;
use super::error::encode_error;
use super::error::error;
use super::rewrite::CaveatError;
use super::rewrite::CheckedCaveat;
use preserves::value::Domain;
use preserves::value::IOValue;
use preserves::value::Map;
use preserves::value::NestedValue;
use preserves::value::Set;
use preserves_schema::support::ParseError;
use std::boxed::Box;
use std::collections::hash_map::HashMap;
use std::convert::TryFrom;
use std::convert::TryInto;
use std::num::NonZeroU64;
use std::sync::Arc;
use std::sync::Mutex;
use std::sync::RwLock;
use std::sync::Weak;
use std::sync::atomic::{AtomicI64, AtomicU64, Ordering};
use tokio::select;
use tokio::sync::Notify;
use tokio::sync::mpsc::{unbounded_channel, UnboundedSender, UnboundedReceiver};
use tokio_util::sync::CancellationToken;
use tracing::Instrument;
/// The type of messages and assertions that can be exchanged among
/// distributed objects, including via [dataspace][crate::dataspace].
///
/// A Preserves value where embedded references are instances of
/// [`Cap`].
///
/// While [`Ref<M>`] can be used within a process, where arbitrary
/// `M`-values can be exchanged among objects, for distributed or
/// polyglot systems a *lingua franca* has to be chosen. `AnyValue` is
/// that language.
pub type AnyValue = super::schemas::internal_protocol::_Any;
/// The type of process-unique actor IDs.
pub type ActorId = u64;
/// The type of process-unique facet IDs.
pub type FacetId = NonZeroU64;
/// The type of process-unique assertion handles.
///
/// Used both as a reference to [retract][Entity::retract]
/// previously-asserted assertions and as an indexing key to associate
/// local state with some incoming assertion in an entity.
pub type Handle = u64;
/// Responses to events must have type `ActorResult`.
pub type ActorResult = Result<(), Error>;
/// The [`Actor::boot`] method returns an `ActorHandle`, representing
/// the actor's mainloop task.
pub type ActorHandle = tokio::task::JoinHandle<ActorResult>;
/// A small protocol for indicating successful synchronisation with
/// some peer; see [Entity::sync].
pub struct Synced;
/// The core metaprotocol implemented by every object.
///
/// Entities communicate with each other by asserting and retracting
/// values and by sending messages (which can be understood very
/// approximately as "infinitesimally brief" assertions of the message
/// body).
///
/// Every assertion placed at a receiving entity *R* from some sending
/// entity *S* lives so long as *S*'s actor survives, *R*'s actor
/// survives, and *S* does not retract the assertion. Messages, by
/// contrast, are transient.
///
/// Implementors of [`Entity`] accept assertions from peers in method
/// [`assert`][Entity::assert]; notification of retraction of a
/// previously-asserted value happens in method
/// [`retract`][Entity::retract]; and notification of a message in
/// method [`message`][Entity::message].
///
/// In addition, entities may *synchronise* with each other: the
/// [`sync`][Entity::sync] method responds to a synchronisation
/// request.
///
/// Finally, the Rust implementation of the Syndicated Actor model
/// offers a hook for running some code at the end of an Entity's
/// containing [`Actor`]'s lifetime
/// ([`exit_hook`][Entity::exit_hook]).
///
/// # What to implement
///
/// The default implementations of the methods here generally do
/// nothing; override them to add actual behaviour to your entity.
///
#[allow(unused_variables)]
pub trait Entity<M>: Send {
/// Receive notification of a new assertion from a peer.
///
/// The `turn` parameter represents the current
/// [activation][Activation]; `assertion` is the value (of type
/// `M`) asserted; and `handle` is the process-unique name for
/// this particular assertion instance that will be used later
/// when it is [retracted][Entity::retract].
///
/// The default implementation does nothing.
fn assert(&mut self, turn: &mut Activation, assertion: M, handle: Handle) -> ActorResult {
Ok(())
}
/// Receive notification of retraction of a previous assertion from a peer.
///
/// This happens either when the asserting peer explicitly
/// retracts an assertion, or when its animating [`Actor`]
/// terminates.
///
/// The `turn` parameter represents the current
/// [activation][Activation], and `handle` is the process-unique
/// name for this particular assertion instance being retracted.
///
/// Note that no `assertion` value is provided: entities needing
/// to know the value that was previously asserted must remember
/// it themselves (perhaps in a [`Map`] keyed by `handle`).
///
/// The default implementation does nothing.
fn retract(&mut self, turn: &mut Activation, handle: Handle) -> ActorResult {
Ok(())
}
/// Receive notification of a message from a peer.
///
/// The `turn` parameter represents the current
/// [activation][Activation], and `message` is the body of the
/// message sent.
///
/// The default implementation does nothing.
fn message(&mut self, turn: &mut Activation, message: M) -> ActorResult {
Ok(())
}
/// Respond to a synchronisation request from a peer.
///
/// Implementors of [`Entity`] will seldom override this. The
/// default implementation fulfils the synchronisation protocol by
/// responding to `peer` with a `Synced` message.
///
/// In special cases, for example when an entity is a proxy for
/// some remote entity, the right thing to do is to forward the
/// synchronisation request on to another entity; in those cases,
/// overriding the default behaviour is appropriate.
fn sync(&mut self, turn: &mut Activation, peer: Arc<Ref<Synced>>) -> ActorResult {
turn.message(&peer, Synced);
Ok(())
}
/// Optional callback for running cleanup actions when the
/// entity's animating [Actor] terminates.
///
/// Programs register an entity's exit hook with
/// [RunningActor::add_exit_hook].
///
/// The default implementation does nothing.
fn exit_hook(&mut self, turn: &mut Activation, exit_status: &Arc<ActorResult>) -> ActorResult {
Ok(())
}
}
/// An "inert" entity, that does nothing in response to any event delivered to it.
///
/// Useful as a placeholder or dummy in various situations.
pub struct InertEntity;
impl<M> Entity<M> for InertEntity {}
enum CleanupAction {
ForMyself(Action),
ForAnother(Arc<Mailbox>, Action),
}
type CleanupActions = Map<Handle, CleanupAction>;
type Action = Box<dyn Send + FnOnce(&mut Activation) -> ActorResult>;
#[doc(hidden)]
pub type PendingEventQueue = Vec<Action>;
/// The main API for programming Syndicated Actor objects.
///
/// Through `Activation`s, programs can access the state of their
/// animating [`RunningActor`] and their active [`Facet`].
///
/// Usually, an `Activation` will be supplied to code that needs one; but when non-Actor code
/// (such as a [linked task][crate::actor#linked-tasks]) needs to enter an Actor's execution
/// context, use [`FacetRef::activate`] to construct one.
///
/// Many actions that an entity can perform are methods directly on
/// `Activation`, but methods on the [`RunningActor`] and [`FacetRef`]
/// values contained in an `Activation` are also sometimes useful.
///
/// This is what other implementations call a "Turn", renamed here to
/// avoid conflicts with [`crate::schemas::internal_protocol::Turn`].
pub struct Activation<'activation> {
/// A reference to the currently active [`Facet`] and the implementation-side state of its
/// [`Actor`].
pub facet: FacetRef,
/// A reference to the current state of the active [`Actor`].
pub state: &'activation mut RunningActor,
pending: EventBuffer,
}
struct EventBuffer {
pub account: Arc<Account>,
queues: HashMap<ActorId, (UnboundedSender<SystemMessage>, PendingEventQueue)>,
for_myself: PendingEventQueue,
}
/// An `Account` records a "debt" in terms of outstanding work items.
///
/// It is part of the flow control mechanism - see [the module-level
/// documentation][crate::actor#flow-control] for more.
#[derive(Debug)]
pub struct Account {
id: u64,
debt: Arc<AtomicI64>,
notify: Notify,
}
/// A `LoanedItem<T>` is a `T` with an associated `cost` recorded
/// against it in the ledger of a given [`Account`]. The cost is
/// repaid automatically when the `LoanedItem<T>` is `Drop`ped.
///
/// `LoanedItem`s are part of the flow control mechanism - see [the
/// module-level documentation][crate::actor#flow-control] for more.
#[derive(Debug)]
pub struct LoanedItem<T> {
/// The account against which this loan is recorded.
pub account: Arc<Account>,
/// The cost of this particular `T`.
pub cost: usize,
/// The underlying item itself.
pub item: T,
}
enum SystemMessage {
Release,
Turn(LoanedItem<PendingEventQueue>),
Crash(Error),
}
/// The mechanism by which events are delivered to a given [`Actor`].
pub struct Mailbox {
/// The ID of the actor this mailbox corresponds to.
pub actor_id: ActorId,
tx: UnboundedSender<SystemMessage>,
}
/// Each actor owns an instance of this structure.
///
/// It holds the receive-half of the actor's mailbox, plus a reference
/// to the actor's private state.
pub struct Actor {
rx: UnboundedReceiver<SystemMessage>,
ac_ref: ActorRef,
}
/// A reference to an actor's private [`ActorState`].
#[derive(Clone)]
pub struct ActorRef {
/// The ID of the referenced actor.
pub actor_id: ActorId,
state: Arc<Mutex<ActorState>>,
}
/// A combination of an [`ActorRef`] with a [`FacetId`], acting as a capability to enter the
/// execution context of a facet from a linked task.
#[derive(Clone)]
pub struct FacetRef {
pub actor: ActorRef,
pub facet_id: FacetId,
}
/// The state of an actor: either `Running` or `Terminated`.
pub enum ActorState {
/// A non-terminated actor has an associated [`RunningActor`] state record.
Running(RunningActor),
/// A terminated actor has an [`ActorResult`] as its `exit_status`.
Terminated {
/// The exit status of the actor: `Ok(())` for normal
/// termination, `Err(_)` for abnormal termination.
exit_status: Arc<ActorResult>,
},
}
/// State associated with each non-terminated [`Actor`].
pub struct RunningActor {
/// The ID of the actor this state belongs to.
pub actor_id: ActorId,
tx: UnboundedSender<SystemMessage>,
mailbox: Weak<Mailbox>,
exit_hooks: Vec<Box<dyn Send + FnOnce(&mut Activation, &Arc<ActorResult>) -> ActorResult>>,
facet_nodes: Map<FacetId, Facet>,
facet_children: Map<FacetId, Set<FacetId>>,
root: FacetId,
}
/// State associated with each facet in an [`Actor`]'s facet tree.
///
/// # Inert facets
///
/// A facet is considered *inert* if:
///
/// 1. it has no child facets;
/// 2. it has no cleanup actions (that is, no assertions placed by any of its entities);
/// 3. it has no linked tasks; and
/// 4. it has no "inert check preventers" (see [Activation::prevent_inert_check]).
///
/// If a facet is created and is inert at the moment that its `boot` function returns, it is
/// automatically terminated.
///
/// When a facet is terminated, if its parent facet is inert, the parent is terminated.
///
/// If the root facet in an actor is terminated, the entire actor is terminated (with exit
/// status `Ok(())`).
///
pub struct Facet {
/// The ID of the facet.
pub facet_id: FacetId,
/// The ID of the facet's parent facet, if any; if None, this facet is the `Actor`'s root facet.
pub parent_facet_id: Option<FacetId>,
cleanup_actions: CleanupActions,
stop_actions: Vec<Action>,
linked_tasks: Map<u64, CancellationToken>,
inert_check_preventers: Arc<AtomicU64>,
}
/// A reference to an object that expects messages/assertions of type
/// `M`.
///
/// The object can be in the same actor, in a different local
/// (in-process) actor, or accessible across a network link.
pub struct Ref<M> {
/// Mailbox of the actor owning the referenced entity.
pub mailbox: Arc<Mailbox>,
/// ID of the facet (within the actor) owning the referenced entity.
pub facet_id: FacetId,
/// Mutex owning and guarding the state backing the referenced entity.
pub target: Mutex<Option<Box<dyn Entity<M>>>>,
}
/// Specialization of `Ref<M>` for messages/assertions of type
/// [`AnyValue`].
///
/// All polyglot and network communication is done in terms of `Cap`s.
///
/// `Cap`s can also be *attenuated* ([Hardy 2017]; [Miller 2006]) to
/// reduce (or otherwise transform) the range of assertions and
/// messages they can be used to send to their referent. The
/// Syndicated Actor model uses
/// [Macaroon](https://syndicate-lang.org/doc/capabilities/)-style
/// capability attenuation.
///
/// [Hardy 2017]: http://cap-lore.com/CapTheory/Patterns/Attenuation.html
/// [Miller 2006]: http://www.erights.org/talks/thesis/markm-thesis.pdf
#[derive(Clone, PartialEq, Eq, Hash, PartialOrd, Ord)]
pub struct Cap {
#[doc(hidden)]
pub underlying: Arc<Ref<AnyValue>>,
#[doc(hidden)]
pub attenuation: Vec<CheckedCaveat>,
}
/// Adapter for converting an underlying [`Ref<M>`] to a [`Cap`].
///
/// The [`Entity`] implementation for `Guard` decodes `AnyValue`
/// assertions/messages to type `M` before passing them on to the
/// underlying entity.
pub struct Guard<M>
where
for<'a> &'a M: Into<AnyValue>,
for<'a> M: TryFrom<&'a AnyValue>,
{
underlying: Arc<Ref<M>>
}
//---------------------------------------------------------------------------
const BUMP_AMOUNT: u8 = 10;
static NEXT_ACTOR_ID: AtomicU64 = AtomicU64::new(1);
#[doc(hidden)]
pub fn next_actor_id() -> ActorId {
NEXT_ACTOR_ID.fetch_add(BUMP_AMOUNT.into(), Ordering::Relaxed)
}
static NEXT_FACET_ID: AtomicU64 = AtomicU64::new(2);
#[doc(hidden)]
pub fn next_facet_id() -> FacetId {
FacetId::new(NEXT_FACET_ID.fetch_add(BUMP_AMOUNT.into(), Ordering::Relaxed))
.expect("Internal error: Attempt to allocate FacetId of zero. Too many FacetIds allocated. Restart the process.")
}
static NEXT_HANDLE: AtomicU64 = AtomicU64::new(3);
/// Allocate a process-unique `Handle`.
pub fn next_handle() -> Handle {
NEXT_HANDLE.fetch_add(BUMP_AMOUNT.into(), Ordering::Relaxed)
}
static NEXT_ACCOUNT_ID: AtomicU64 = AtomicU64::new(4);
static NEXT_TASK_ID: AtomicU64 = AtomicU64::new(5);
preserves_schema::support::lazy_static! {
#[doc(hidden)]
pub static ref SYNDICATE_CREDIT: i64 = {
let credit =
std::env::var("SYNDICATE_CREDIT").unwrap_or("100".to_owned())
.parse::<i64>().expect("Valid SYNDICATE_CREDIT environment variable");
tracing::debug!("Configured SYNDICATE_CREDIT = {}", credit);
credit
};
#[doc(hidden)]
pub static ref ACCOUNTS: RwLock<Map<u64, (tracing::Span, Arc<AtomicI64>)>> =
RwLock::new(Map::new());
}
impl TryFrom<&AnyValue> for Synced {
type Error = ParseError;
fn try_from(value: &AnyValue) -> Result<Self, Self::Error> {
if let Some(true) = value.value().as_boolean() {
Ok(Synced)
} else {
Err(ParseError::conformance_error("Synced"))
}
}
}
impl From<&Synced> for AnyValue {
fn from(_value: &Synced) -> Self {
AnyValue::new(true)
}
}
impl FacetRef {
/// Executes `f` in a new "[turn][Activation]" for `actor`. If `f` returns `Ok(())`,
/// [commits the turn][Activation::deliver] and performs the buffered actions; otherwise,
/// [abandons the turn][Activation::clear] and discards the buffered actions.
///
/// Bills any activity to `account`.
pub fn activate<F>(
&self,
account: Arc<Account>,
f: F,
) -> ActorResult where
F: FnOnce(&mut Activation) -> ActorResult,
{
match self.activate_exit(account, |t| match f(t) {
Ok(()) => None,
Err(e) => Some(Err(e)),
}) {
None => Ok(()),
Some(e) => Err(error("Could not activate terminated actor", encode_error(e))),
}
}
/// Executes `f` in a new "[turn][Activation]" for `actor`. If `f` returns
/// `Some(exit_status)`, terminates `actor` with that `exit_status`. Otherwise, if `f`
/// returns `None`, leaves `actor` in runnable state. [Commits buffered
/// actions][Activation::deliver] unless `actor` terminates with an `Err` status.
///
/// Bills any activity to `account`.
pub fn activate_exit<F>(
&self,
account: Arc<Account>,
f: F,
) -> Option<ActorResult> where
F: FnOnce(&mut Activation) -> Option<ActorResult>,
{
match self.actor.state.lock() {
Err(_) => panicked_err(),
Ok(mut g) => match &mut *g {
ActorState::Terminated { exit_status } =>
Some((**exit_status).clone()),
ActorState::Running(state) => {
let mut activation = Activation::make(self, account, state);
match f(&mut activation) {
None => None,
Some(exit_status) => {
if exit_status.is_err() {
activation.clear();
}
drop(activation);
let exit_status = Arc::new(exit_status);
let mut t = Activation::make(&self.actor.facet_ref(state.root),
Account::new(crate::name!("shutdown")),
state);
for action in std::mem::take(&mut t.state.exit_hooks) {
if let Err(err) = action(&mut t, &exit_status) {
tracing::error!(err = debug(err), "error in exit hook");
}
}
if let Err(err) = t._terminate_facet(t.state.root, false) {
// This can only occur as the result of an internal error in this file's code.
tracing::error!(err = debug(err), "unexpected error from disorderly terminate_facet");
panic!("Unexpected error result from disorderly terminate_facet");
}
*g = ActorState::Terminated {
exit_status: Arc::clone(&exit_status),
};
Some((*exit_status).clone())
}
}
}
}
}
}
}
impl<'activation> Activation<'activation> {
fn make(
facet: &FacetRef,
account: Arc<Account>,
state: &'activation mut RunningActor,
) -> Self {
Activation {
facet: facet.clone(),
state,
pending: EventBuffer::new(account),
}
}
fn immediate_oid<M>(&self, r: &Arc<Ref<M>>) {
if r.mailbox.actor_id != self.facet.actor.actor_id {
panic!("Cannot use for_myself to send to remote peers");
}
}
fn with_facet<F>(&mut self, check_existence: bool, facet_id: FacetId, f: F) -> ActorResult
where
F: FnOnce(&mut Activation) -> ActorResult,
{
if !check_existence || self.state.facet_nodes.contains_key(&facet_id) {
let old_facet_id = self.facet.facet_id;
self.facet.facet_id = facet_id;
let result = f(self);
self.facet.facet_id = old_facet_id;
result
} else {
Ok(())
}
}
#[doc(hidden)]
pub fn with_entity<M, F>(&mut self, r: &Arc<Ref<M>>, f: F) -> ActorResult where
F: FnOnce(&mut Activation, &mut dyn Entity<M>) -> ActorResult
{
self.with_facet(true, r.facet_id, |t| r.internal_with_entity(|e| f(t, e)))
}
fn active_facet<'a>(&'a mut self) -> Option<&'a mut Facet> {
self.state.get_facet(self.facet.facet_id)
}
/// Core API: assert `a` at recipient `r`.
///
/// Returns the [`Handle`] for the new assertion.
pub fn assert<M: 'static + Send>(&mut self, r: &Arc<Ref<M>>, a: M) -> Handle {
let handle = next_handle();
if let Some(f) = self.active_facet() {
{
let r = Arc::clone(r);
f.cleanup_actions.insert(
handle,
CleanupAction::ForAnother(Arc::clone(&r.mailbox), Box::new(
move |t| t.with_entity(&r, |t, e| e.retract(t, handle)))));
}
drop(f);
{
let r = Arc::clone(r);
self.pending.queue_for(&r).push(Box::new(
move |t| t.with_entity(&r, |t, e| e.assert(t, a, handle))));
}
}
handle
}
/// Core API: assert `a` at `r`, which must be a `Ref<M>` within the active actor.
///
/// It's perfectly OK to use method [`assert`][Self::assert] even
/// for `Ref`s that are part of the active actor. The difference
/// between `assert` and `assert_for_myself` is that `r`'s handler
/// for `assert` runs in a separate, later [`Activation`], while
/// `r`'s handler for `assert_for_myself` runs in *this*
/// [`Activation`], before it commits.
///
/// Returns the [`Handle`] for the new assertion.
///
/// # Panics
///
/// Panics if `r` is not part of the active actor.
pub fn assert_for_myself<M: 'static + Send>(&mut self, r: &Arc<Ref<M>>, a: M) -> Handle {
self.immediate_oid(r);
let handle = next_handle();
if let Some(f) = self.active_facet() {
{
let r = Arc::clone(r);
f.cleanup_actions.insert(
handle,
CleanupAction::ForMyself(Box::new(
move |t| t.with_entity(&r, |t, e| e.retract(t, handle)))));
}
drop(f);
{
let r = Arc::clone(r);
self.pending.for_myself.push(Box::new(
move |t| t.with_entity(&r, |t, e| e.assert(t, a, handle))));
}
}
handle
}
/// Core API: retract a previously-established assertion.
pub fn retract(&mut self, handle: Handle) {
if let Some(f) = self.active_facet() {
if let Some(d) = f.cleanup_actions.remove(&handle) {
self.pending.execute_cleanup_action(d)
}
}
}
/// Core API: send message `m` to recipient `r`.
pub fn message<M: 'static + Send>(&mut self, r: &Arc<Ref<M>>, m: M) {
let r = Arc::clone(r);
self.pending.queue_for(&r).push(Box::new(
move |t| t.with_entity(&r, |t, e| e.message(t, m))))
}
/// Core API: send message `m` to recipient `r`, which must be a
/// `Ref<M>` within the active actor.
///
/// Method `message_for_myself` is to [`message`][Self::message]
/// as [`assert_for_myself`][Self::assert_for_myself] is to
/// [`assert`][Self::assert].
///
/// # Panics
///
/// Panics if `r` is not part of the active actor.
pub fn message_for_myself<M: 'static + Send>(&mut self, r: &Arc<Ref<M>>, m: M) {
self.immediate_oid(r);
let r = Arc::clone(r);
self.pending.for_myself.push(Box::new(
move |t| t.with_entity(&r, |t, e| e.message(t, m))))
}
/// Core API: begins a synchronisation with `r`.
///
/// Once the synchronisation request reaches `r`'s actor, it will
/// send a response to `peer`, which acts as a continuation for
/// the synchronisation request.
pub fn sync<M: 'static + Send>(&mut self, r: &Arc<Ref<M>>, peer: Arc<Ref<Synced>>) {
let r = Arc::clone(r);
self.pending.queue_for(&r).push(Box::new(
move |t| t.with_entity(&r, |t, e| e.sync(t, peer))))
}
/// Retrieve the [`Account`] against which actions are recorded.
pub fn account(&self) -> &Arc<Account> {
&self.pending.account
}
/// Discards all pending actions in this activation.
pub fn clear(&mut self) {
self.pending.clear();
}
/// Delivers all pending actions in this activation.
///
/// This is called automatically when an `Activation` is
/// `Drop`ped.
///
/// # Panics
///
/// Panics if any pending actions "`for_myself`" (resulting from
/// [`assert_for_myself`][Self::assert_for_myself] or
/// [`message_for_myself`][Self::message_for_myself]) are
/// outstanding at the time of the call.
pub fn deliver(&mut self) {
self.pending.deliver();
}
/// Construct an entity with behaviour [`InertEntity`] within the active facet.
pub fn inert_entity<M>(&mut self) -> Arc<Ref<M>> {
self.create(InertEntity)
}
/// Construct an entity with behaviour `e` within the active facet.
pub fn create<M, E: Entity<M> + Send + 'static>(&mut self, e: E) -> Arc<Ref<M>> {
let r = self.create_inert();
r.become_entity(e);
r
}
/// Construct an entity (within the active facet) whose behaviour will be specified later
/// via [`become_entity`][Ref::become_entity].
pub fn create_inert<M>(&mut self) -> Arc<Ref<M>> {
Arc::new(Ref {
mailbox: self.state.mailbox(),
facet_id: self.facet.facet_id,
target: Mutex::new(None),
})
}
/// Start a new [linked task][crate::actor#linked-tasks] attached to the active facet. The
/// task will execute the future "`boot`" to completion unless it is cancelled first (by
/// e.g. termination of the owning facet or crashing of the owning actor). Uses `name` for
/// log messages emitted by the task.
pub fn linked_task<F: 'static + Send + futures::Future<Output = ActorResult>>(
&mut self,
name: tracing::Span,
boot: F,
) {
let mailbox = self.state.mailbox();
if let Some(f) = self.active_facet() {
let token = CancellationToken::new();
let task_id = NEXT_TASK_ID.fetch_add(1, Ordering::Relaxed);
name.record("task_id", &task_id);
{
let token = token.clone();
tokio::spawn(async move {
tracing::trace!(task_id, "linked task start");
select! {
_ = token.cancelled() => {
tracing::trace!(task_id, "linked task cancelled");
Ok(())
}
result = boot => {
match &result {
Ok(()) => {
tracing::trace!(task_id, "linked task normal stop");
()
}
Err(e) => {
tracing::error!(task_id, "linked task error: {}", e);
let _ = mailbox.tx.send(SystemMessage::Crash(e.clone()));
()
}
}
result
}
}
}.instrument(name));
}
f.linked_tasks.insert(task_id, token);
}
}
fn enqueue_for_myself_at_commit(&mut self, action: Action) {
let mailbox = self.state.mailbox();
self.pending.queue_for_mailbox(&mailbox).push(action);
}
/// Schedule the creation of a new actor when the Activation commits.
pub fn spawn<F: 'static + Send + FnOnce(&mut Activation) -> ActorResult>(
&mut self,
name: tracing::Span,
boot: F,
) {
self.enqueue_for_myself_at_commit(Box::new(move |_| {
Actor::new().boot(name, boot);
Ok(())
}));
}
/// Create a new subfacet of the currently-active facet. Runs `boot` in the new facet's
/// context. If `boot` returns leaving the new facet [inert][Facet#inert-facets],
pub fn facet<F: 'static + Send + FnOnce(&mut Activation) -> ActorResult>(
&mut self,
boot: F,
) -> Result<FacetId, Error> {
let f = Facet::new(Some(self.facet.facet_id));
let facet_id = f.facet_id;
self.state.facet_nodes.insert(facet_id, f);
self.state.facet_children.entry(self.facet.facet_id).or_default().insert(facet_id);
self.with_facet(true /* TODO: tiny optimisation: "false" would be safe here */, facet_id, move |t| {
boot(t)?;
t.stop_if_inert();
Ok(())
})?;
Ok(facet_id)
}
/// Useful during facet (and actor) startup, in some situations: when a facet `boot`
/// procedure would return while the facet is inert, but the facet should survive until
/// some subsequent time, call `prevent_inert_check` to increment a counter that prevents
/// inertness-checks from succeeding on the active facet.
///
/// The result of `prevent_inert_check` is a function which, when called, decrements the
/// counter again. After the counter has been decremented, any subsequent inertness checks
/// will no longer be artificially forced to fail.
///
/// An example of when you might want this: creating an actor having only a single
/// Dataspace entity within it, then using the Dataspace from other actors. At the start of
/// its life, the Dataspace actor will have no outbound assertions, no child facets, and no
/// linked tasks, so the only way to prevent it from being prematurely garbage collected is
/// to use `prevent_inert_check` in its boot function.
pub fn prevent_inert_check(&mut self) -> Box<dyn FnOnce()> {
if let Some(f) = self.active_facet() {
Box::new(f.prevent_inert_check())
} else {
Box::new(|| ())
}
}
/// Arranges for the [`Facet`] named by `facet_id` to be stopped cleanly when `self`
/// commits. If `continuation` is supplied, the facet to be stopped hasn't been stopped
/// yet, none of the shutdown handlers yields an error, and the facet's parent facet is
/// alive, executes `continuation` in the parent facet's context.
pub fn stop_facet(&mut self, facet_id: FacetId, continuation: Option<Action>) {
let maybe_parent_id = self.active_facet().and_then(|f| f.parent_facet_id);
self.enqueue_for_myself_at_commit(Box::new(move |t| {
t._terminate_facet(facet_id, true)?;
if let Some(k) = continuation {
if let Some(parent_id) = maybe_parent_id {
t.with_facet(true, parent_id, k)?;
}
}
Ok(())
}));
}
/// Arranges for the active facet to be stopped cleanly when `self` commits.
///
/// Equivalent to `self.stop_facet(self.facet_id.unwrap(), None)`.
pub fn stop(&mut self) {
self.stop_facet(self.facet.facet_id, None)
}
fn stop_if_inert(&mut self) {
if self.state.facet_exists_and_is_inert(self.facet.facet_id) {
self.stop_facet(self.facet.facet_id, None);
}
}
fn _terminate_facet(&mut self, facet_id: FacetId, orderly: bool) -> ActorResult {
if let Some(mut f) = self.state.facet_nodes.remove(&facet_id) {
tracing::debug!("{} terminating {:?}",
if orderly { "orderly" } else { "disorderly" },
facet_id);
if let Some(p) = f.parent_facet_id {
self.state.facet_children.get_mut(&p).map(|children| children.remove(&facet_id));
}
self.with_facet(false, facet_id, |t| {
if let Some(children) = t.state.facet_children.remove(&facet_id) {
for child_id in children.into_iter() {
t._terminate_facet(child_id, orderly)?;
}
}
if orderly {
for action in std::mem::take(&mut f.stop_actions) {
action(t)?;
}
let parent_facet_id = f.parent_facet_id;
// if !orderly, the drop will happen at the end of this function, but we
// need it to happen right here so that child-facet cleanup-actions are
// performed before parent-facet cleanup-actions.
drop(f);
if let Some(p) = parent_facet_id {
if t.state.facet_exists_and_is_inert(p) {
t._terminate_facet(p, true)?;
}
} else {
t.state.shutdown();
}
}
Ok(())
})
} else {
Ok(())
}
}
}
impl EventBuffer {
fn new(account: Arc<Account>) -> Self {
EventBuffer {
account,
queues: HashMap::new(),
for_myself: Vec::new(),
}
}
fn execute_cleanup_action(&mut self, d: CleanupAction) {
match d {
CleanupAction::ForAnother(mailbox, action) =>
self.queue_for_mailbox(&mailbox).push(action),
CleanupAction::ForMyself(action) =>
self.for_myself.push(action),
}
}
fn queue_for<M>(&mut self, r: &Arc<Ref<M>>) -> &mut PendingEventQueue {
self.queue_for_mailbox(&r.mailbox)
}
fn queue_for_mailbox(&mut self, mailbox: &Arc<Mailbox>) -> &mut PendingEventQueue {
&mut self.queues.entry(mailbox.actor_id)
.or_insert((mailbox.tx.clone(), Vec::new())).1
}
fn clear(&mut self) {
self.queues = HashMap::new();
self.for_myself = PendingEventQueue::new();
}
fn deliver(&mut self) {
if !self.for_myself.is_empty() {
panic!("Unprocessed for_myself events remain at deliver() time");
}
for (_actor_id, (tx, turn)) in std::mem::take(&mut self.queues).into_iter() {
let _ = send_actions(&tx, &self.account, turn);
}
}
}
impl Drop for EventBuffer {
fn drop(&mut self) {
self.deliver()
}
}
impl Account {
/// Construct a new `Account`, storing `name` within it for
/// debugging use.
pub fn new(name: tracing::Span) -> Arc<Self> {
let id = NEXT_ACCOUNT_ID.fetch_add(1, Ordering::Relaxed);
let debt = Arc::new(AtomicI64::new(0));
ACCOUNTS.write().unwrap().insert(id, (name, Arc::clone(&debt)));
Arc::new(Account {
id,
debt,
notify: Notify::new(),
})
}
/// Retrieve the current account balance: the number of
/// currently-outstanding work items.
pub fn balance(&self) -> i64 {
self.debt.load(Ordering::Relaxed)
}
/// Borrow `token_count` work items against this account.
pub fn borrow(&self, token_count: usize) {
let token_count: i64 = token_count.try_into().expect("manageable token count");
self.debt.fetch_add(token_count, Ordering::Relaxed);
}
/// Repay `token_count` work items previously borrowed against this account.
pub fn repay(&self, token_count: usize) {
let token_count: i64 = token_count.try_into().expect("manageable token count");
let _old_debt = self.debt.fetch_sub(token_count, Ordering::Relaxed);
if _old_debt - token_count <= *SYNDICATE_CREDIT {
self.notify.notify_one();
}
}
/// Suspend execution until enough "clear funds" exist in this
/// account for some subsequent activity to be permissible.
pub async fn ensure_clear_funds(&self) {
let limit = *SYNDICATE_CREDIT;
// tokio::task::yield_now().await;
while self.balance() > limit {
// tokio::task::yield_now().await;
self.notify.notified().await;
}
}
}
impl Drop for Account {
fn drop(&mut self) {
ACCOUNTS.write().unwrap().remove(&self.id);
}
}
impl<T> LoanedItem<T> {
/// Construct a new `LoanedItem<T>` containing `item`, recording
/// `cost` work items against `account`.
pub fn new(account: &Arc<Account>, cost: usize, item: T) -> Self {
account.borrow(cost);
LoanedItem { account: Arc::clone(account), cost, item }
}
}
impl<T> Drop for LoanedItem<T> {
fn drop(&mut self) {
self.account.repay(self.cost);
}
}
#[must_use]
fn send_actions(
tx: &UnboundedSender<SystemMessage>,
account: &Arc<Account>,
t: PendingEventQueue,
) -> ActorResult {
let token_count = t.len();
tx.send(SystemMessage::Turn(LoanedItem::new(account, token_count, t)))
.map_err(|_| error("Target actor not running", AnyValue::new(false)))
}
impl std::fmt::Debug for Mailbox {
fn fmt(&self, f: &mut std::fmt::Formatter) -> Result<(), std::fmt::Error> {
write!(f, "#<Mailbox {}>", self.actor_id)
}
}
impl std::hash::Hash for Mailbox {
fn hash<H: std::hash::Hasher>(&self, state: &mut H) {
self.actor_id.hash(state)
}
}
impl Eq for Mailbox {}
impl PartialEq for Mailbox {
fn eq(&self, other: &Mailbox) -> bool {
self.actor_id == other.actor_id
}
}
impl Ord for Mailbox {
fn cmp(&self, other: &Mailbox) -> std::cmp::Ordering {
return self.actor_id.cmp(&other.actor_id)
}
}
impl PartialOrd for Mailbox {
fn partial_cmp(&self, other: &Mailbox) -> Option<std::cmp::Ordering> {
return Some(self.cmp(&other))
}
}
impl Drop for Mailbox {
fn drop(&mut self) {
let _ = self.tx.send(SystemMessage::Release);
()
}
}
impl Actor {
/// Create a new actor. It still needs to be [`boot`ed][Self::boot].
pub fn new() -> Self {
let (tx, rx) = unbounded_channel();
let actor_id = next_actor_id();
let root = Facet::new(None);
// tracing::trace!(id = actor_id, "Actor::new");
let mut st = RunningActor {
actor_id,
tx,
mailbox: Weak::new(),
exit_hooks: Vec::new(),
facet_nodes: Map::new(),
facet_children: Map::new(),
root: root.facet_id,
};
st.facet_nodes.insert(root.facet_id, root);
Actor {
rx,
ac_ref: ActorRef {
actor_id,
state: Arc::new(Mutex::new(ActorState::Running(st))),
},
}
}
/// Start the actor's mainloop. Takes ownership of `self`. The
/// `name` is used as context for any log messages emitted by the
/// actor. The `boot` function is called in the actor's context,
/// and then the mainloop is entered.
pub fn boot<F: 'static + Send + FnOnce(&mut Activation) -> ActorResult>(
mut self,
name: tracing::Span,
boot: F,
) -> ActorHandle {
name.record("actor_id", &self.ac_ref.actor_id);
tokio::spawn(async move {
tracing::trace!("start");
self.run(|t| {
boot(t)?;
t.stop_if_inert();
Ok(())
}).await;
let result = self.ac_ref.exit_status().expect("terminated");
match &result {
Ok(()) => tracing::trace!("normal stop"),
Err(e) => tracing::error!("error stop: {}", e),
}
result
}.instrument(name))
}
async fn run<F: 'static + Send + FnOnce(&mut Activation) -> ActorResult>(
&mut self,
boot: F,
) -> () {
let root = self.ac_ref.access(|s| match s.expect("New actor missing its state") {
ActorState::Terminated { .. } => panic!("New actor unexpectedly in terminated state"),
ActorState::Running(ra) => ra.root, // what a lot of work to get this one number
});
let root_facet_ref = self.ac_ref.facet_ref(root);
let terminate = |result: ActorResult| {
let _ = root_facet_ref.activate_exit(Account::new(crate::name!("shutdown")),
|_| Some(result));
};
if root_facet_ref.activate(Account::new(crate::name!("boot")), boot).is_err() {
return;
}
loop {
match self.rx.recv().await {
None => {
return terminate(Err(error("Unexpected channel close", AnyValue::new(false))));
}
Some(m) => match m {
SystemMessage::Release => {
tracing::trace!("SystemMessage::Release");
return terminate(Ok(()));
}
SystemMessage::Turn(mut loaned_item) => {
let mut actions = std::mem::take(&mut loaned_item.item);
let r = root_facet_ref.activate(Arc::clone(&loaned_item.account), |t| {
loop {
for action in actions.into_iter() { action(t)? }
actions = std::mem::take(&mut t.pending.for_myself);
if actions.is_empty() { break; }
}
Ok(())
});
if r.is_err() { return; }
}
SystemMessage::Crash(e) => {
tracing::trace!("SystemMessage::Crash({:?})", &e);
return terminate(Err(e));
}
}
}
}
}
}
impl Facet {
fn new(parent_facet_id: Option<FacetId>) -> Self {
Facet {
facet_id: next_facet_id(),
parent_facet_id,
cleanup_actions: Map::new(),
stop_actions: Vec::new(),
linked_tasks: Map::new(),
inert_check_preventers: Arc::new(AtomicU64::new(0)),
}
}
fn prevent_inert_check(&mut self) -> impl FnOnce() {
let inert_check_preventers = Arc::clone(&self.inert_check_preventers);
let armed = AtomicU64::new(1);
inert_check_preventers.fetch_add(1, Ordering::Relaxed);
move || {
match armed.compare_exchange(1, 0, Ordering::SeqCst, Ordering::SeqCst) {
Ok(_) => {
inert_check_preventers.fetch_sub(1, Ordering::Relaxed);
()
}
Err(_) => (),
}
}
}
}
fn panicked_err() -> Option<ActorResult> {
Some(Err(error("Actor panicked", AnyValue::new(false))))
}
impl ActorRef {
/// Uses an internal mutex to access the internal state: takes the
/// lock, calls `f` with the internal state, releases the lock,
/// and returns the result of `f`.
pub fn access<R, F: FnOnce(Option<&mut ActorState>) -> R>(&self, f: F) -> R {
match self.state.lock() {
Err(_) => f(None),
Ok(mut g) => f(Some(&mut *g)),
}
}
/// Retrieves the exit status of the denoted actor. If it is still
/// running, yields `None`; otherwise, yields `Some(Ok(()))` if it
/// exited normally, or `Some(Err(_))` if it terminated
/// abnormally.
pub fn exit_status(&self) -> Option<ActorResult> {
self.access(|s| s.map_or_else(
panicked_err,
|state| match state {
ActorState::Running(_) => None,
ActorState::Terminated { exit_status } => Some((**exit_status).clone()),
}))
}
fn facet_ref(&self, facet_id: FacetId) -> FacetRef {
FacetRef {
actor: self.clone(),
facet_id,
}
}
}
impl RunningActor {
/// Requests a shutdown of the actor. The shutdown request is
/// handled by the actor's main loop, causing it to terminate with
/// exit status `Ok(())`.
pub fn shutdown(&self) {
let _ = self.tx.send(SystemMessage::Release);
}
fn mailbox(&mut self) -> Arc<Mailbox> {
match self.mailbox.upgrade() {
None => {
let new_mailbox = Arc::new(Mailbox {
actor_id: self.actor_id,
tx: self.tx.clone(),
});
self.mailbox = Arc::downgrade(&new_mailbox);
new_mailbox
}
Some(m) => m
}
}
/// Registers the entity `r` in the list of exit hooks for this
/// actor. When the actor terminates, `r`'s
/// [`exit_hook`][Entity::exit_hook] will be called.
pub fn add_exit_hook<M: 'static + Send>(&mut self, r: &Arc<Ref<M>>) {
let r = Arc::clone(r);
self.exit_hooks.push(Box::new(
move |t, exit_status| r.internal_with_entity(|e| e.exit_hook(t, &exit_status))))
}
fn get_facet(&mut self, facet_id: FacetId) -> Option<&mut Facet> {
self.facet_nodes.get_mut(&facet_id)
}
/// See the definition of an [inert facet][Facet#inert-facets].
fn facet_exists_and_is_inert(&mut self, facet_id: FacetId) -> bool {
let no_kids = self.facet_children.get(&facet_id).map(|cs| cs.is_empty()).unwrap_or(true);
if let Some(f) = self.get_facet(facet_id) {
no_kids &&
f.cleanup_actions.is_empty() &&
f.linked_tasks.is_empty() &&
f.inert_check_preventers.load(Ordering::Relaxed) == 0
} else {
false
}
}
}
impl Drop for Actor {
fn drop(&mut self) {
self.rx.close();
}
}
impl Drop for Facet {
fn drop(&mut self) {
for (_task_id, token) in std::mem::take(&mut self.linked_tasks).into_iter() {
token.cancel();
}
let to_clear = std::mem::take(&mut self.cleanup_actions);
{
let mut b = EventBuffer::new(Account::new(crate::name!("drop")));
for (_handle, r) in to_clear.into_iter() {
tracing::trace!(h = debug(&_handle), "retract on termination");
b.execute_cleanup_action(r);
}
}
tracing::trace!(facet_id = debug(self.facet_id), "Facet::drop");
}
}
/// Directly injects `action` into `mailbox`, billing subsequent activity against `account`.
///
/// Primarily for use by [linked tasks][Activation::linked_task].
#[must_use]
pub fn external_event(mailbox: &Arc<Mailbox>, account: &Arc<Account>, action: Action) -> ActorResult {
send_actions(&mailbox.tx, account, vec![action])
}
/// Directly injects `actions` into `mailbox`, billing subsequent activity against `account`.
///
/// Primarily for use by [linked tasks][Activation::linked_task].
#[must_use]
pub fn external_events(mailbox: &Arc<Mailbox>, account: &Arc<Account>, actions: PendingEventQueue) -> ActorResult {
send_actions(&mailbox.tx, account, actions)
}
impl<M> Ref<M> {
/// Supplies the behaviour (`e`) for a `Ref` created via
/// [`create_inert`][Activation::create_inert].
///
/// # Panics
///
/// Panics if this `Ref` has already been given a behaviour.
pub fn become_entity<E: 'static + Entity<M>>(&self, e: E) {
let mut g = self.target.lock().expect("unpoisoned");
if g.is_some() {
panic!("Double initialization of Ref");
}
*g = Some(Box::new(e));
}
fn internal_with_entity<R, F: FnOnce(&mut dyn Entity<M>) -> R>(&self, f: F) -> R {
let mut g = self.target.lock().expect("unpoisoned");
f(g.as_mut().expect("initialized").as_mut())
}
}
impl<M> Ref<M> {
/// Retrieves a process-unique identifier for the `Ref`; `Ref`s
/// are compared by this identifier.
pub fn oid(&self) -> usize {
std::ptr::addr_of!(*self) as usize
}
}
impl<M> PartialEq for Ref<M> {
fn eq(&self, other: &Self) -> bool {
self.oid() == other.oid()
}
}
impl<M> Eq for Ref<M> {}
impl<M> std::hash::Hash for Ref<M> {
fn hash<H>(&self, hash: &mut H) where H: std::hash::Hasher {
self.oid().hash(hash)
}
}
impl<M> PartialOrd for Ref<M> {
fn partial_cmp(&self, other: &Self) -> Option<std::cmp::Ordering> {
Some(self.cmp(other))
}
}
impl<M> Ord for Ref<M> {
fn cmp(&self, other: &Self) -> std::cmp::Ordering {
self.oid().cmp(&other.oid())
}
}
impl<M> std::fmt::Debug for Ref<M> {
fn fmt(&self, f: &mut std::fmt::Formatter) -> Result<(), std::fmt::Error> {
write!(f, "⌜{}:{:016x}⌝", self.mailbox.actor_id, self.oid())
}
}
impl Cap {
/// Given a `Ref<M>`, where `M` is interconvertible with
/// `AnyValue`, yields a `Cap` for the referenced entity. The
/// `Cap` automatically decodes presented `AnyValue`s into
/// instances of `M`.
pub fn guard<M: 'static + Send>(underlying: &Arc<Ref<M>>) -> Arc<Self>
where
for<'a> &'a M: Into<AnyValue>,
for<'a> M: TryFrom<&'a AnyValue>,
{
Self::new(&Arc::new(Ref {
mailbox: Arc::clone(&underlying.mailbox),
facet_id: underlying.facet_id,
target: Mutex::new(Some(Box::new(Guard { underlying: underlying.clone() }))),
}))
}
/// Directly constructs a `Cap` for `underlying`.
pub fn new(underlying: &Arc<Ref<AnyValue>>) -> Arc<Self> {
Arc::new(Cap {
underlying: Arc::clone(underlying),
attenuation: Vec::new(),
})
}
/// Yields a fresh `Cap` for `self`'s `underlying`, copying the
/// existing attenuation of `self` to the new `Cap` and adding
/// `attenuation` to it.
pub fn attenuate(&self, attenuation: &sturdy::Attenuation) -> Result<Arc<Self>, CaveatError> {
let mut r = Cap { attenuation: self.attenuation.clone(), .. self.clone() };
r.attenuation.extend(attenuation.check()?);
Ok(Arc::new(r))
}
/// Applies the contained attenuation to `a`, yielding `None` if
/// `a` is filtered out, or `Some(_)` if it is accepted (and
/// possibly transformed).
pub fn rewrite(&self, mut a: AnyValue) -> Option<AnyValue> {
for c in &self.attenuation {
match c.rewrite(&a) {
Some(v) => a = v,
None => return None,
}
}
Some(a)
}
/// Translates `m` into an `AnyValue`, passes it through
/// [`rewrite`][Self::rewrite], and then
/// [`assert`s][Activation::assert] it using the activation `t`.
pub fn assert<M: Into<AnyValue>>(&self, t: &mut Activation, m: M) -> Option<Handle> {
self.rewrite(m.into()).map(|m| t.assert(&self.underlying, m))
}
/// Translates `m` into an `AnyValue`, passes it through
/// [`rewrite`][Self::rewrite], and then sends it via method
/// [`message`][Activation::message] on the activation `t`.
pub fn message<M: Into<AnyValue>>(&self, t: &mut Activation, m: M) {
if let Some(m) = self.rewrite(m.into()) {
t.message(&self.underlying, m)
}
}
}
impl std::fmt::Debug for Cap {
fn fmt(&self, f: &mut std::fmt::Formatter) -> Result<(), std::fmt::Error> {
if self.attenuation.is_empty() {
self.underlying.fmt(f)
} else {
write!(f, "⌜{}:{:016x}\\{:?}⌝",
self.underlying.mailbox.actor_id,
self.underlying.oid(),
self.attenuation)
}
}
}
impl Domain for Cap {}
impl std::convert::TryFrom<&IOValue> for Cap {
type Error = preserves_schema::support::ParseError;
fn try_from(_v: &IOValue) -> Result<Self, Self::Error> {
panic!("Attempted to serialize Cap via IOValue");
}
}
impl std::convert::From<&Cap> for IOValue {
fn from(_v: &Cap) -> IOValue {
panic!("Attempted to deserialize Ref via IOValue");
}
}
impl<M> Entity<AnyValue> for Guard<M>
where
for<'a> &'a M: Into<AnyValue>,
for<'a> M: TryFrom<&'a AnyValue>,
{
fn assert(&mut self, t: &mut Activation, a: AnyValue, h: Handle) -> ActorResult {
match M::try_from(&a) {
Ok(a) => t.with_entity(&self.underlying, |t, e| e.assert(t, a, h)),
Err(_) => Ok(()),
}
}
fn retract(&mut self, t: &mut Activation, h: Handle) -> ActorResult {
t.with_entity(&self.underlying, |t, e| e.retract(t, h))
}
fn message(&mut self, t: &mut Activation, m: AnyValue) -> ActorResult {
match M::try_from(&m) {
Ok(m) => t.with_entity(&self.underlying, |t, e| e.message(t, m)),
Err(_) => Ok(()),
}
}
fn sync(&mut self, t: &mut Activation, peer: Arc<Ref<Synced>>) -> ActorResult {
t.with_entity(&self.underlying, |t, e| e.sync(t, peer))
}
fn exit_hook(&mut self, t: &mut Activation, exit_status: &Arc<ActorResult>) -> ActorResult {
self.underlying.internal_with_entity(|e| e.exit_hook(t, exit_status))
}
}
/// A convenient Syndicate-enhanced variation on
/// [`tracing::info_span`].
///
/// Includes fields `actor_id`, `task_id` and `oid`, so that they show
/// up in those circumstances where they happen to be defined as part
/// of the operation of the [`crate::actor`] module.
#[macro_export]
macro_rules! name {
() => {tracing::info_span!(actor_id = tracing::field::Empty,
task_id = tracing::field::Empty,
oid = tracing::field::Empty)};
($($item:tt)*) => {tracing::info_span!($($item)*,
actor_id = tracing::field::Empty,
task_id = tracing::field::Empty,
oid = tracing::field::Empty)}
}
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