compute_ctl: return LSN in /terminate (#12240)

- Add optional `?mode=fast|immediate` to `/terminate`, `fast` is
default. Immediate avoids waiting 30
  seconds before returning from `terminate`.
- Add `TerminateMode` to `ComputeStatus::TerminationPending`
- Use `/terminate?mode=immediate` in `neon_local` instead of `pg_ctl
stop` for `test_replica_promotes`.
- Change `test_replica_promotes` to check returned LSN
- Annotate `finish_sync_safekeepers` as `noreturn`.

https://github.com/neondatabase/cloud/issues/29807

compute_tools/src/http/routes/terminate.rs

@@ -1,29 +1,39 @@
-use std::sync::Arc;
-
+use crate::compute::{ComputeNode, forward_termination_signal};
+use crate::http::JsonResponse;
 use axum::extract::State;
-use axum::response::{IntoResponse, Response};
-use compute_api::responses::ComputeStatus;
+use axum::response::Response;
+use axum_extra::extract::OptionalQuery;
+use compute_api::responses::{ComputeStatus, TerminateResponse};
 use http::StatusCode;
+use serde::Deserialize;
+use std::sync::Arc;
 use tokio::task;
 use tracing::info;
 
-use crate::compute::{ComputeNode, forward_termination_signal};
-use crate::http::JsonResponse;
+#[derive(Deserialize, Default)]
+pub struct TerminateQuery {
+    mode: compute_api::responses::TerminateMode,
+}
 
 /// Terminate the compute.
-pub(in crate::http) async fn terminate(State(compute): State<Arc<ComputeNode>>) -> Response {
+pub(in crate::http) async fn terminate(
+    State(compute): State<Arc<ComputeNode>>,
+    OptionalQuery(terminate): OptionalQuery<TerminateQuery>,
+) -> Response {
+    let mode = terminate.unwrap_or_default().mode;
     {
         let mut state = compute.state.lock().unwrap();
         if state.status == ComputeStatus::Terminated {
-            return StatusCode::CREATED.into_response();
+            return JsonResponse::success(StatusCode::CREATED, state.terminate_flush_lsn);
         }
 
         if !matches!(state.status, ComputeStatus::Empty | ComputeStatus::Running) {
             return JsonResponse::invalid_status(state.status);
         }
-
-        state.set_status(ComputeStatus::TerminationPending, &compute.state_changed);
-        drop(state);
+        state.set_status(
+            ComputeStatus::TerminationPending { mode },
+            &compute.state_changed,
+        );
     }
 
     forward_termination_signal(false);
@@ -34,7 +44,7 @@ pub(in crate::http) async fn terminate(State(compute): State<Arc<ComputeNode>>)
     // be able to serve other requests while some particular request
     // is waiting for compute to finish configuration.
     let c = compute.clone();
-    task::spawn_blocking(move || {
+    let lsn = task::spawn_blocking(move || {
         let mut state = c.state.lock().unwrap();
         while state.status != ComputeStatus::Terminated {
             state = c.state_changed.wait(state).unwrap();
@@ -44,11 +54,10 @@ pub(in crate::http) async fn terminate(State(compute): State<Arc<ComputeNode>>)
                 state.status
             );
         }
+        state.terminate_flush_lsn
     })
     .await
     .unwrap();
-
     info!("terminated Postgres");
-
-    StatusCode::OK.into_response()
+    JsonResponse::success(StatusCode::OK, TerminateResponse { lsn })
 }