fix: make major worker tasks managed separately from the user worker

(cherry picked from commit a80bf00)

Author: nyannyacha

crates/base/src/rt_worker/rt.rs

@@ -8,7 +8,13 @@ pub static SUPERVISOR_RT: Lazy<tokio::runtime::Runtime> = Lazy::new(|| {
         .unwrap()
 });
 
-pub static WORKER_RT: Lazy<tokio_util::task::LocalPoolHandle> = Lazy::new(|| {
+// NOTE: This pool is for the main and event workers. The reason why they should
+// separate from the user worker pool is they can starve them if user workers
+// are saturated.
+pub static PRIMARY_WORKER_RT: Lazy<tokio_util::task::LocalPoolHandle> =
+    Lazy::new(|| tokio_util::task::LocalPoolHandle::new(2));
+
+pub static USER_WORKER_RT: Lazy<tokio_util::task::LocalPoolHandle> = Lazy::new(|| {
     let maybe_pool_size = std::env::var("EDGE_RUNTIME_WORKER_POOL_SIZE")
         .ok()
         .and_then(|it| it.parse::<usize>().ok());

crates/base/src/rt_worker/worker.rs

@@ -98,8 +98,13 @@ impl Worker {
         let is_user_worker = opts.conf.is_user_worker();
 
         let cancel = self.cancel.clone();
+        let rt = if is_user_worker {
+            &rt::USER_WORKER_RT
+        } else {
+            &rt::PRIMARY_WORKER_RT
+        };
 
-        let _worker_handle = rt::WORKER_RT.spawn_pinned(move || {
+        let _worker_handle = rt.spawn_pinned(move || {
             tokio::task::spawn_local(async move {
                 let (maybe_cpu_usage_metrics_tx, maybe_cpu_usage_metrics_rx) = is_user_worker
                     .then(unbounded_channel::<CPUUsageMetrics>)