add unconstrained feature to service worker

Signed-off-by: Jason Volk <jason@zemos.net>

src/service/manager.rs

@@ -1,7 +1,7 @@
 use std::{panic::AssertUnwindSafe, sync::Arc, time::Duration};
 
 use conduwuit::{debug, debug_warn, error, trace, utils::time, warn, Err, Error, Result, Server};
-use futures::FutureExt;
+use futures::{FutureExt, TryFutureExt};
 use tokio::{
 	sync::{Mutex, MutexGuard},
 	task::{JoinHandle, JoinSet},
@@ -183,9 +183,14 @@ async fn worker(service: Arc<dyn Service>) -> WorkerResult {
 	let service_ = Arc::clone(&service);
 	let result = AssertUnwindSafe(service_.worker())
 		.catch_unwind()
-		.await
 		.map_err(Error::from_panic);
 
+	let result = if service.unconstrained() {
+		tokio::task::unconstrained(result).await
+	} else {
+		result.await
+	};
+
 	// flattens JoinError for panic into worker's Error
 	(service, result.unwrap_or_else(Err))
 }

src/service/sending/mod.rs

@@ -22,7 +22,7 @@ use ruma::{
 	RoomId, ServerName, UserId,
 };
 use smallvec::SmallVec;
-use tokio::task::JoinSet;
+use tokio::{task, task::JoinSet};
 
 use self::data::Data;
 pub use self::{
@@ -111,8 +111,15 @@ impl crate::Service for Service {
 				.enumerate()
 				.fold(JoinSet::new(), |mut joinset, (id, _)| {
 					let self_ = self.clone();
+					let worker = self_.sender(id);
+					let worker = if self.unconstrained() {
+						task::unconstrained(worker).boxed()
+					} else {
+						worker.boxed()
+					};
+
 					let runtime = self.server.runtime();
-					let _abort = joinset.spawn_on(self_.sender(id).boxed(), runtime);
+					let _abort = joinset.spawn_on(worker, runtime);
 					joinset
 				});
 
@@ -139,6 +146,8 @@ impl crate::Service for Service {
 	}
 
 	fn name(&self) -> &str { crate::service::make_name(std::module_path!()) }
+
+	fn unconstrained(&self) -> bool { true }
 }
 
 impl Service {

src/service/service.rs

@@ -39,6 +39,11 @@ pub(crate) trait Service: Any + Send + Sync {
 	/// Return the name of the service.
 	/// i.e. `crate::service::make_name(std::module_path!())`
 	fn name(&self) -> &str;
+
+	/// Return true if the service worker opts out of the tokio cooperative
+	/// budgeting. This can reduce tail latency at the risk of event loop
+	/// starvation.
+	fn unconstrained(&self) -> bool { false }
 }
 
 /// Args are passed to `Service::build` when a service is constructed. This