From dfc131850a09e7ceacfa98315adbef156e07e9ca Mon Sep 17 00:00:00 2001
From: Alex Auvolat <alex@adnab.me>
Date: Wed, 14 Dec 2022 15:25:29 +0100
Subject: Simplified and more aggressive worker exit logic

---
 src/util/background/worker.rs | 73 ++++++++++++++-----------------------------
 1 file changed, 23 insertions(+), 50 deletions(-)

(limited to 'src/util/background')

diff --git a/src/util/background/worker.rs b/src/util/background/worker.rs
index 7e9da7f8..8165e2cb 100644
--- a/src/util/background/worker.rs
+++ b/src/util/background/worker.rs
@@ -1,6 +1,6 @@
 use std::collections::HashMap;
 use std::sync::Arc;
-use std::time::{Duration, Instant};
+use std::time::Duration;
 
 use async_trait::async_trait;
 use futures::future::*;
@@ -14,6 +14,10 @@ use crate::background::{WorkerInfo, WorkerStatus};
 use crate::error::Error;
 use crate::time::now_msec;
 
+// All workers that haven't exited for this time after an exit signal was recieved
+// will be interrupted in the middle of whatever they are doing.
+const EXIT_DEADLINE: Duration = Duration::from_secs(8);
+
 #[derive(PartialEq, Copy, Clone, Serialize, Deserialize, Debug)]
 pub enum WorkerState {
 	Busy,
@@ -50,10 +54,8 @@ pub trait Worker: Send {
 	async fn work(&mut self, must_exit: &mut watch::Receiver<bool>) -> Result<WorkerState, Error>;
 
 	/// Wait for work: await for some task to become available.  This future can be interrupted in
-	/// the middle for any reason.  This future doesn't have to await on must_exit.changed(), we
-	/// are doing it for you.  Therefore it only receives a read refernce to must_exit which allows
-	/// it to check if we are exiting.
-	async fn wait_for_work(&mut self, must_exit: &watch::Receiver<bool>) -> WorkerState;
+	/// the middle for any reason, for example if an interrupt signal was recieved.
+	async fn wait_for_work(&mut self) -> WorkerState;
 }
 
 pub(crate) struct WorkerProcessor {
@@ -93,11 +95,9 @@ impl WorkerProcessor {
 						let task_id = next_task_id;
 						next_task_id += 1;
 						let stop_signal = self.stop_signal.clone();
-						let stop_signal_worker = self.stop_signal.clone();
 						let mut worker = WorkerHandler {
 								task_id,
 								stop_signal,
-								stop_signal_worker,
 								worker: new_worker,
 								state: WorkerState::Busy,
 								errors: 0,
@@ -153,26 +153,14 @@ impl WorkerProcessor {
 		}
 
 		// We are exiting, drain everything
-		let drain_half_time = Instant::now() + Duration::from_secs(5);
 		let drain_everything = async move {
-			while let Some(mut worker) = workers.next().await {
-				if worker.state == WorkerState::Done {
-					info!(
-						"Worker {} (TID {}) exited",
-						worker.worker.name(),
-						worker.task_id
-					);
-				} else if Instant::now() > drain_half_time {
-					warn!("Worker {} (TID {}) interrupted between two iterations in state {:?} (this should be fine)", worker.worker.name(), worker.task_id, worker.state);
-				} else {
-					workers.push(
-						async move {
-							worker.step().await;
-							worker
-						}
-						.boxed(),
-					);
-				}
+			while let Some(worker) = workers.next().await {
+				info!(
+					"Worker {} (TID {}) exited (last state: {:?})",
+					worker.worker.name(),
+					worker.task_id,
+					worker.state
+				);
 			}
 		};
 
@@ -180,7 +168,7 @@ impl WorkerProcessor {
 			_ = drain_everything => {
 				info!("All workers exited peacefully \\o/");
 			}
-			_ = tokio::time::sleep(Duration::from_secs(9)) => {
+			_ = tokio::time::sleep(EXIT_DEADLINE) => {
 				error!("Some workers could not exit in time, we are cancelling some things in the middle");
 			}
 		}
@@ -190,7 +178,6 @@ impl WorkerProcessor {
 struct WorkerHandler {
 	task_id: usize,
 	stop_signal: watch::Receiver<bool>,
-	stop_signal_worker: watch::Receiver<bool>,
 	worker: Box<dyn Worker>,
 	state: WorkerState,
 	errors: usize,
@@ -225,33 +212,19 @@ impl WorkerHandler {
 			},
 			WorkerState::Throttled(delay) => {
 				// Sleep for given delay and go back to busy state
-				if !*self.stop_signal.borrow() {
-					select! {
-						_ = tokio::time::sleep(Duration::from_secs_f32(delay)) => (),
-						_ = self.stop_signal.changed() => (),
+				select! {
+					_ = tokio::time::sleep(Duration::from_secs_f32(delay)) => {
+						self.state = WorkerState::Busy;
 					}
+					_ = self.stop_signal.changed() => (),
 				}
-				self.state = WorkerState::Busy;
 			}
 			WorkerState::Idle => {
-				if *self.stop_signal.borrow() {
-					select! {
-						new_st = self.worker.wait_for_work(&self.stop_signal_worker) => {
-							self.state = new_st;
-						}
-						_ = tokio::time::sleep(Duration::from_secs(1)) => {
-							// stay in Idle state
-						}
-					}
-				} else {
-					select! {
-						new_st = self.worker.wait_for_work(&self.stop_signal_worker) => {
-							self.state = new_st;
-						}
-						_ = self.stop_signal.changed() => {
-							// stay in Idle state
-						}
+				select! {
+					new_st = self.worker.wait_for_work() => {
+						self.state = new_st;
 					}
+					_ = self.stop_signal.changed() => (),
 				}
 			}
 			WorkerState::Done => unreachable!(),
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