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use std::{
sync::Arc,
time::{Duration, Instant},
};
use crate::{
ActivationStrategy, Backend, TaskDefinition, Worker, WorkerFactory,
backends::{ClaimTaskError, FinishTaskError, RenewTaskError},
};
use tokio::sync::mpsc::UnboundedSender as MpscSender;
use tracing::{trace, warn};
const LEASE_DURATION: Duration = Duration::from_secs(20);
const LEASE_RENEWAL_THRESHOLD: Duration = Duration::from_secs(10);
/// An internal type that handles worker lifecycle.
#[derive(Debug)]
pub(crate) struct WorkerRuntime<B, F> {
pub backend: B,
pub factory: Arc<F>,
pub worker_id: u64,
pub finished_signal: MpscSender<()>,
}
impl<B, F> WorkerRuntime<B, F>
where
B: Backend + 'static,
F: WorkerFactory + 'static,
{
pub fn run(
self,
dispatch_token: <<<F::Worker as Worker>::Task as TaskDefinition>::Trigger as ActivationStrategy>::DispatchToken,
) {
let daemon = Daemon {
backend: self.backend,
factory: self.factory,
worker_id: self.worker_id,
finished_signal: self.finished_signal,
status: DaemonStatus::WaitingForTask { dispatch_token },
};
tokio::spawn(daemon.run());
}
}
struct Daemon<B, F, T>
where
T: TaskDefinition,
{
backend: B,
factory: Arc<F>,
worker_id: u64,
finished_signal: MpscSender<()>,
status: DaemonStatus<T>,
}
impl<B, F> Daemon<B, F, <F::Worker as Worker>::Task>
where
B: Backend,
F: WorkerFactory,
F::Worker: 'static,
{
async fn run(mut self) {
loop {
let (new_self, action) = self.event_loop().await;
self = new_self;
if matches!(action, EventLoopResult::Exit) {
break;
}
}
let _ = self.finished_signal.send(());
}
async fn event_loop(mut self) -> (Self, EventLoopResult) {
let (status, action) = match self.status {
DaemonStatus::WaitingForTask { dispatch_token } => {
match <<<F::Worker as Worker>::Task as TaskDefinition>::Trigger as ActivationStrategy>::claim_task::<B, <F::Worker as Worker>::Task>(
&self.backend,
self.worker_id,
dispatch_token,
Instant::now() + LEASE_DURATION,
)
.await {
Ok(task) => (
DaemonStatus::TaskClaimed {
task_id: task.task_id,
task_payload: task.task_payload,
lease_expiration: task.lease_expiration,
},
EventLoopResult::Continue,
),
Err(ClaimTaskError::TaskLeased { .. } | ClaimTaskError::TaskNotFound) => {
// This is fine as it's likely that another worker claimed the task.
trace!("Unable to claim task with worker #{}", self.worker_id);
(DaemonStatus::WorkerExited, EventLoopResult::Exit)
}
Err(ClaimTaskError::Backend(err)) => {
warn!(
"Unable to claim task with worker #{} due to backend error: {}",
self.worker_id, err
);
(DaemonStatus::WorkerExited, EventLoopResult::Exit)
}
}
}
DaemonStatus::TaskClaimed {
task_id,
task_payload,
lease_expiration,
} => {
let worker = self.factory.build(self.worker_id);
let worker_handle =
tokio::spawn(async move { worker.process(task_id, task_payload).await });
(
DaemonStatus::WorkerStarted {
task_id,
worker_handle,
lease_expiration,
},
EventLoopResult::Continue,
)
}
DaemonStatus::WorkerStarted {
task_id,
mut worker_handle,
lease_expiration,
} => {
let renewal_deadline = lease_expiration
.checked_sub(LEASE_RENEWAL_THRESHOLD)
.unwrap_or_else(Instant::now);
let renewal =
tokio::time::sleep_until(tokio::time::Instant::from_std(renewal_deadline));
tokio::select! {
_ = renewal => {
let renewal = self
.backend
.renew(
self.worker_id,
task_id,
Instant::now() + LEASE_DURATION,
)
.await;
match renewal {
Ok(new_lease) => {
trace!("Lease renewed");
(
DaemonStatus::WorkerStarted {
task_id,
worker_handle,
lease_expiration: new_lease.new_expiration,
},
EventLoopResult::Continue,
)
}
Err(RenewTaskError::LeaseLost) => {
trace!(
"Lease lost for task #{}, aborting worker #{}",
task_id,
self.worker_id
);
worker_handle.abort();
(DaemonStatus::WorkerExited, EventLoopResult::Exit)
}
Err(RenewTaskError::Backend(err)) => {
warn!(
"Unable to renew lease for task #{} with worker #{}: {}",
task_id,
self.worker_id,
err
);
worker_handle.abort();
(DaemonStatus::WorkerExited, EventLoopResult::Exit)
}
}
},
join_result = &mut worker_handle => {
match join_result {
Ok(callback_payload) => (
DaemonStatus::WorkerFinishedProcessing {
task_id,
callback_payload,
},
EventLoopResult::Continue,
),
Err(err) => {
// TODO: Handle post-failure state. Potential options:
// - give up lease to allow immediate take over
// - set up retry-after mechanism for retrying with backoff
warn!(
"Worker #{} for task #{} exited unexpectedly: {}",
self.worker_id,
task_id,
err
);
(DaemonStatus::WorkerExited, EventLoopResult::Exit)
}
}
},
}
}
DaemonStatus::WorkerFinishedProcessing {
task_id,
callback_payload,
} => {
match self
.backend
.finish::<<F::Worker as Worker>::Task>(
self.worker_id,
task_id,
callback_payload,
)
.await
{
Ok(_) => {
trace!("Finished task #{} with worker #{}", task_id, self.worker_id);
}
Err(FinishTaskError::LeaseLost) => {
warn!(
"Worker #{} finished task #{} but no longer holds its lease; assuming another worker took over",
self.worker_id, task_id
);
}
Err(FinishTaskError::Backend(err)) => {
warn!(
"Unable to finalize task #{} with worker #{} due to backend error: {}",
task_id, self.worker_id, err
);
}
}
(DaemonStatus::WorkerExited, EventLoopResult::Exit)
}
DaemonStatus::WorkerExited => {
unreachable!("Worker runtime event loop should have ended")
}
};
self.status = status;
(self, action)
}
}
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
enum EventLoopResult {
Continue,
Exit,
}
/// Worker runtime daemon lifecycle stages.
enum DaemonStatus<T>
where
T: TaskDefinition,
{
/// The runtime has just been started and have not claimed the task yet.
WaitingForTask {
dispatch_token: <T::Trigger as ActivationStrategy>::DispatchToken,
},
/// The runtime has claimed the task.
TaskClaimed {
task_id: u64,
task_payload: <T::Trigger as ActivationStrategy>::EffectivePayload,
lease_expiration: Instant,
},
/// The background worker has been spawned.
WorkerStarted {
task_id: u64,
worker_handle: tokio::task::JoinHandle<T::Callback>,
lease_expiration: Instant,
},
/// The worker future completed successfully and the task should be finalized in the backend.
WorkerFinishedProcessing {
task_id: u64,
callback_payload: T::Callback,
},
/// The worker runtime is done.
WorkerExited,
}