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improve automations interface #1709

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Oct 16, 2024
Merged

improve automations interface #1709

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114 changes: 48 additions & 66 deletions crates/automations/src/executors.rs
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Original file line number Diff line number Diff line change
@@ -1,4 +1,4 @@
use super::{server, BoxedRaw, Executor, PollOutcome, TaskType};
use super::{server, Action, BoxedRaw, Executor, Outcome, TaskType};
use anyhow::Context;
use futures::future::{BoxFuture, FutureExt};
use sqlx::types::Json as SqlJson;
Expand All @@ -9,11 +9,12 @@ pub trait ObjSafe: Send + Sync + 'static {

fn poll<'s>(
&'s self,
pool: &'s sqlx::PgPool,
task_id: models::Id,
parent_id: Option<models::Id>,
state: &'s mut Option<SqlJson<BoxedRaw>>,
inbox: &'s mut Option<Vec<SqlJson<(models::Id, Option<BoxedRaw>)>>>,
) -> BoxFuture<'s, anyhow::Result<PollOutcome<BoxedRaw>>>;
state: Option<SqlJson<BoxedRaw>>,
inbox: Option<Vec<SqlJson<(models::Id, Option<BoxedRaw>)>>>,
) -> BoxFuture<'s, anyhow::Result<()>>;
}

impl<E: Executor> ObjSafe for E {
Expand All @@ -23,11 +24,12 @@ impl<E: Executor> ObjSafe for E {

fn poll<'s>(
&'s self,
pool: &'s sqlx::PgPool,
task_id: models::Id,
parent_id: Option<models::Id>,
state: &'s mut Option<SqlJson<BoxedRaw>>,
inbox: &'s mut Option<Vec<SqlJson<(models::Id, Option<BoxedRaw>)>>>,
) -> BoxFuture<'s, anyhow::Result<PollOutcome<BoxedRaw>>> {
mut state: Option<SqlJson<BoxedRaw>>,
mut inbox: Option<Vec<SqlJson<(models::Id, Option<BoxedRaw>)>>>,
) -> BoxFuture<'s, anyhow::Result<()>> {
async move {
let mut state_parsed: E::State = if let Some(state) = state {
serde_json::from_str(state.get()).context("failed to decode task state")?
Expand All @@ -52,6 +54,7 @@ impl<E: Executor> ObjSafe for E {

let outcome = E::poll(
self,
pool,
task_id,
parent_id,
&mut state_parsed,
Expand All @@ -60,21 +63,16 @@ impl<E: Executor> ObjSafe for E {
.await?;

// Re-encode state for persistence.
// If we're Done, then the output state is NULL which is implicitly Default.
if matches!(outcome, PollOutcome::Done) {
*state = None
} else {
*state = Some(SqlJson(
serde_json::value::to_raw_value(&state_parsed)
.context("failed to encode inner state")?,
));
}
state = Some(SqlJson(
serde_json::value::to_raw_value(&state_parsed)
.context("failed to encode inner state")?,
));

// Re-encode the unconsumed portion of the inbox.
if inbox_parsed.is_empty() {
*inbox = None
inbox = None
} else {
*inbox = Some(
inbox = Some(
inbox_parsed
.into_iter()
.map(|(task_id, msg)| {
Expand All @@ -91,19 +89,16 @@ impl<E: Executor> ObjSafe for E {
);
}

Ok(match outcome {
PollOutcome::Done => PollOutcome::Done,
PollOutcome::Send(task_id, msg) => PollOutcome::Send(task_id, msg),
PollOutcome::Sleep(interval) => PollOutcome::Sleep(interval),
PollOutcome::Spawn(task_id, task_type, msg) => {
PollOutcome::Spawn(task_id, task_type, msg)
}
PollOutcome::Suspend => PollOutcome::Suspend,
PollOutcome::Yield(msg) => PollOutcome::Yield(
serde_json::value::to_raw_value(&msg)
.context("failed to encode yielded message")?,
),
})
let mut txn = pool.begin().await?;

let action = outcome
.apply(&mut *txn)
.await
.context("failed to apply task Outcome")?;

() = persist_action(action, &mut *txn, task_id, parent_id, state, inbox).await?;

Ok(txn.commit().await?)
}
.boxed()
}
Expand All @@ -119,8 +114,8 @@ pub async fn poll_task(
id: task_id,
type_: _,
parent_id,
mut inbox,
mut state,
inbox,
state,
mut last_heartbeat,
},
}: server::ReadyTask,
Expand All @@ -145,24 +140,9 @@ pub async fn poll_task(

// Poll `executor` and `update_heartbeats` in tandem, so that a failure
// to update our heartbeat also cancels the executor.
let outcome = tokio::select! {
outcome = executor.poll(task_id, parent_id, &mut state, &mut inbox) => { outcome? },
err = &mut update_heartbeats => return Err(err),
};

// The possibly long-lived polling operation is now complete.
// Build a Future that commits a (hopefully) brief transaction of `outcome`.
let persist_outcome = async {
let mut txn = pool.begin().await?;
() = persist_outcome(outcome, &mut *txn, task_id, parent_id, state, inbox).await?;
Ok(txn.commit().await?)
};

// Poll `persist_outcome` while continuing to poll `update_heartbeats`,
// to guarantee we cannot commit an outcome after our lease is lost.
tokio::select! {
result = persist_outcome => result,
err = update_heartbeats => Err(err),
result = executor.poll(&pool, task_id, parent_id, state, inbox) => result,
err = &mut update_heartbeats => return Err(err),
}
}

Expand Down Expand Up @@ -203,17 +183,17 @@ async fn update_heartbeat(
Ok(updated.heartbeat)
}

async fn persist_outcome(
outcome: PollOutcome<BoxedRaw>,
async fn persist_action(
action: Action,
txn: &mut sqlx::PgConnection,
task_id: models::Id,
parent_id: Option<models::Id>,
state: Option<SqlJson<BoxedRaw>>,
mut state: Option<SqlJson<BoxedRaw>>,
inbox: Option<Vec<SqlJson<(models::Id, Option<BoxedRaw>)>>>,
) -> anyhow::Result<()> {
use std::time::Duration;

if let PollOutcome::Spawn(spawn_id, spawn_type, _msg) = &outcome {
if let Action::Spawn(spawn_id, spawn_type, _msg) = &action {
sqlx::query!(
"SELECT internal.create_task($1, $2, $3)",
*spawn_id as models::Id,
Expand All @@ -225,15 +205,15 @@ async fn persist_outcome(
.context("failed to spawn new task")?;
}

if let Some((send_id, msg)) = match &outcome {
if let Some((send_id, msg)) = match &action {
// When a task is spawned, send its first message.
PollOutcome::Spawn(spawn_id, _spawn_type, msg) => Some((*spawn_id, Some(msg))),
Action::Spawn(spawn_id, _spawn_type, msg) => Some((*spawn_id, Some(msg))),
// If we're Done but have a parent, send it an EOF.
PollOutcome::Done => parent_id.map(|parent_id| (parent_id, None)),
Action::Done => parent_id.map(|parent_id| (parent_id, None)),
// Send an arbitrary message to an identified task.
PollOutcome::Send(task_id, msg) => Some((*task_id, msg.as_ref())),
Action::Send(task_id, msg) => Some((*task_id, msg.as_ref())),
// Yield is sugar for sending to our parent.
PollOutcome::Yield(msg) => {
Action::Yield(msg) => {
let Some(parent_id) = parent_id else {
anyhow::bail!("task yielded illegally, because it does not have a parent");
};
Expand All @@ -255,17 +235,19 @@ async fn persist_outcome(
let wake_at_interval = if inbox.is_some() {
Some(Duration::ZERO) // Always poll immediately if inbox items remain.
} else {
match &outcome {
PollOutcome::Sleep(interval) => Some(*interval),
match &action {
Action::Sleep(interval) => Some(*interval),
// These outcomes do not suspend the task, and it should wake as soon as possible.
PollOutcome::Spawn(..) | PollOutcome::Send(..) | PollOutcome::Yield(..) => {
Some(Duration::ZERO)
}
Action::Spawn(..) | Action::Send(..) | Action::Yield(..) => Some(Duration::ZERO),
// Suspend indefinitely (note that NOW() + NULL::INTERVAL is NULL).
PollOutcome::Done | PollOutcome::Suspend => None,
Action::Done | Action::Suspend => None,
}
};

if let Action::Done = &action {
state = None; // Set to NULL, which is implicit Default.
}

let updated = sqlx::query!(
r#"
UPDATE internal.tasks SET
Expand All @@ -292,7 +274,7 @@ async fn persist_outcome(

// If we're Done and also successfully suspended, then delete ourselves.
// (Otherwise, the task has been left in a like-new state).
if matches!(&outcome, PollOutcome::Done if updated.suspended) {
if matches!(&action, Action::Done if updated.suspended) {
sqlx::query!(
"DELETE FROM internal.tasks WHERE task_id = $1;",
task_id as models::Id,
Expand Down
53 changes: 45 additions & 8 deletions crates/automations/src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -23,16 +23,40 @@ type BoxedRaw = Box<serde_json::value::RawValue>;
#[sqlx(transparent)]
pub struct TaskType(pub i16);

/// PollOutcome is the outcome of an `Executor::poll()` for a given task.
/// Outcome of an `Executor::poll()` for a given task, which encloses
/// an Action with which it's applied as a single transaction.
///
/// As an example of how Executor, Outcome, and Action are used together,
/// suppose an implementation of `Executor::poll()` is called:
///
/// - It reads DB state associated with the task using sqlx::PgPool.
/// - It performs long-running work, running outside of a DB transaction.
/// - It returns an Outcome implementation which encapsulates the
/// preconditions it observed, as well as its domain-specific outcome.
/// - `Outcome::apply()` is called and re-verifies preconditions using `txn`,
/// returning an error if preconditions have changed.
/// - It applies the effects of its outcome and returns a polling Action.
/// - `txn` is further by this crate as required by the Action, and then commits.
///
pub trait Outcome: Send {
/// Apply the effects of an Executor poll. While this is an async routine,
/// apply() runs in the context of a held transaction and should be fast.
fn apply<'s>(
self,
txn: &'s mut sqlx::PgConnection,
) -> impl std::future::Future<Output = anyhow::Result<Action>> + Send + 's;
}

/// Action undertaken by an Executor task poll.
#[derive(Debug)]
pub enum PollOutcome<Yield> {
pub enum Action {
/// Spawn a new TaskId with the given TaskType and send a first message.
/// The TaskId must not exist.
Spawn(models::Id, TaskType, BoxedRaw),
/// Send a message (Some) or EOF (None) to another TaskId, which must exist.
Send(models::Id, Option<BoxedRaw>),
/// Yield to send a message to this task's parent.
Yield(Yield),
Yield(BoxedRaw),
/// Sleep for at-most the indicated Duration, then poll again.
/// The task may be woken earlier if it receives a message.
Sleep(std::time::Duration),
Expand All @@ -43,28 +67,35 @@ pub enum PollOutcome<Yield> {
Done,
}

// Action implements an Outcome with no side-effects.
impl Outcome for Action {
async fn apply<'s>(self, _txn: &'s mut sqlx::PgConnection) -> anyhow::Result<Action> {
Ok(self)
}
}

/// Executor is the core trait implemented by executors of various task types.
pub trait Executor: Send + Sync + 'static {
const TASK_TYPE: TaskType;

type Receive: serde::de::DeserializeOwned + serde::Serialize + Send;
type State: Default + serde::de::DeserializeOwned + serde::Serialize + Send;
type Yield: serde::Serialize;
type Outcome: Outcome;

fn poll<'s>(
&'s self,
pool: &'s sqlx::PgPool,
task_id: models::Id,
parent_id: Option<models::Id>,
state: &'s mut Self::State,
inbox: &'s mut std::collections::VecDeque<(models::Id, Option<Self::Receive>)>,
) -> impl std::future::Future<Output = anyhow::Result<PollOutcome<Self::Yield>>> + Send + 's;
) -> impl std::future::Future<Output = anyhow::Result<Self::Outcome>> + Send + 's;
}

/// Server holds registered implementations of Executor,
/// and serves them.
/// Server holds registered implementations of Executors and serves them.
pub struct Server(Vec<Arc<dyn executors::ObjSafe>>);

impl<Yield> PollOutcome<Yield> {
impl Action {
pub fn spawn<M: serde::Serialize>(
spawn_id: models::Id,
task_type: TaskType,
Expand All @@ -89,6 +120,12 @@ impl<Yield> PollOutcome<Yield> {
},
))
}

pub fn yield_<M: serde::Serialize>(msg: M) -> anyhow::Result<Self> {
Ok(Self::Yield(
serde_json::value::to_raw_value(&msg).context("failed to encode yielded message")?,
))
}
}

pub fn next_task_id() -> models::Id {
Expand Down
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