lsp: Parse LSP messages on background thread - again (#23122)

This is a follow-up to #12640.
While profiling latency of working with a project with 8192 diagnostics
I've noticed that while we're parsing the LSP messages into a generic
message struct on a background thread, we can still block the main
thread as the conversion between that generic message struct and the
actual LSP message (for use by callback) is still happening on the main
thread.
This PR significantly constrains what a message callback can use, so
that it can be executed on any thread; we also send off message
conversion to the background thread. In practice new callback
constraints were already satisfied by all call sites, so no code outside
of the lsp crate had to be adjusted.

This has improved throughput of my 8192-benchmark from 40s to send out
all diagnostics after saving to ~20s. Now main thread is spending most
of the time updating our diagnostics sets, which can probably be
improved too.

Closes #ISSUE

Release Notes:

- Improved app responsiveness with huge # of diagnostics.

crates/collab/src/tests/integration_tests.rs

@@ -4206,6 +4206,7 @@ async fn test_collaborating_with_lsp_progress_updates_and_diagnostics_ordering(
                 }],
             },
         );
+        executor.run_until_parked();
     }
     fake_language_server.notify::<lsp::notification::Progress>(&lsp::ProgressParams {
         token: lsp::NumberOrString::String("the-disk-based-token".to_string()),

crates/editor/src/test/editor_lsp_test_context.rs

@@ -315,12 +315,12 @@ impl EditorLspTestContext {
 
     pub fn handle_request<T, F, Fut>(
         &self,
-        mut handler: F,
+        handler: F,
     ) -> futures::channel::mpsc::UnboundedReceiver<()>
     where
         T: 'static + request::Request,
         T::Params: 'static + Send,
-        F: 'static + Send + FnMut(lsp::Url, T::Params, gpui::AsyncAppContext) -> Fut,
+        F: 'static + Send + Sync + Fn(lsp::Url, T::Params, gpui::AsyncAppContext) -> Fut,
         Fut: 'static + Send + Future<Output = Result<T::Result>>,
     {
         let url = self.buffer_lsp_url.clone();

crates/lsp/src/lsp.rs

@@ -45,7 +45,7 @@ const CONTENT_LEN_HEADER: &str = "Content-Length: ";
 const LSP_REQUEST_TIMEOUT: Duration = Duration::from_secs(60 * 2);
 const SERVER_SHUTDOWN_TIMEOUT: Duration = Duration::from_secs(5);
 
-type NotificationHandler = Box<dyn Send + FnMut(Option<RequestId>, Value, AsyncAppContext)>;
+type NotificationHandler = Arc<dyn Send + Sync + Fn(Option<RequestId>, Value, AsyncAppContext)>;
 type ResponseHandler = Box<dyn Send + FnOnce(Result<String, Error>)>;
 type IoHandler = Box<dyn Send + FnMut(IoKind, &str)>;
 
@@ -890,7 +890,7 @@ impl LanguageServer {
     pub fn on_notification<T, F>(&self, f: F) -> Subscription
     where
         T: notification::Notification,
-        F: 'static + Send + FnMut(T::Params, AsyncAppContext),
+        F: 'static + Send + Sync + Fn(T::Params, AsyncAppContext),
     {
         self.on_custom_notification(T::METHOD, f)
     }
@@ -903,7 +903,7 @@ impl LanguageServer {
     where
         T: request::Request,
         T::Params: 'static + Send,
-        F: 'static + FnMut(T::Params, AsyncAppContext) -> Fut + Send,
+        F: 'static + Fn(T::Params, AsyncAppContext) -> Fut + Send + Sync,
         Fut: 'static + Future<Output = Result<T::Result>>,
     {
         self.on_custom_request(T::METHOD, f)
@@ -939,17 +939,27 @@ impl LanguageServer {
     }
 
     #[must_use]
-    fn on_custom_notification<Params, F>(&self, method: &'static str, mut f: F) -> Subscription
+    fn on_custom_notification<Params, F>(&self, method: &'static str, f: F) -> Subscription
     where
-        F: 'static + FnMut(Params, AsyncAppContext) + Send,
-        Params: DeserializeOwned,
+        F: 'static + Fn(Params, AsyncAppContext) + Send + Sync,
+        Params: DeserializeOwned + Send + 'static,
     {
+        let callback = Arc::new(f);
         let prev_handler = self.notification_handlers.lock().insert(
             method,
-            Box::new(move |_, params, cx| {
-                if let Some(params) = serde_json::from_value(params).log_err() {
-                    f(params, cx);
-                }
+            Arc::new(move |_, params, cx| {
+                let callback = callback.clone();
+
+                cx.spawn(move |cx| async move {
+                    if let Some(params) = cx
+                        .background_executor()
+                        .spawn(async move { serde_json::from_value(params).log_err() })
+                        .await
+                    {
+                        callback(params, cx);
+                    }
+                })
+                .detach();
             }),
         );
         assert!(
@@ -963,64 +973,74 @@ impl LanguageServer {
     }
 
     #[must_use]
-    fn on_custom_request<Params, Res, Fut, F>(&self, method: &'static str, mut f: F) -> Subscription
+    fn on_custom_request<Params, Res, Fut, F>(&self, method: &'static str, f: F) -> Subscription
     where
-        F: 'static + FnMut(Params, AsyncAppContext) -> Fut + Send,
+        F: 'static + Fn(Params, AsyncAppContext) -> Fut + Send + Sync,
         Fut: 'static + Future<Output = Result<Res>>,
         Params: DeserializeOwned + Send + 'static,
         Res: Serialize,
     {
         let outbound_tx = self.outbound_tx.clone();
+        let f = Arc::new(f);
         let prev_handler = self.notification_handlers.lock().insert(
             method,
-            Box::new(move |id, params, cx| {
+            Arc::new(move |id, params, cx| {
                 if let Some(id) = id {
-                    match serde_json::from_value(params) {
-                        Ok(params) => {
-                            let response = f(params, cx.clone());
-                            cx.foreground_executor()
-                                .spawn({
-                                    let outbound_tx = outbound_tx.clone();
-                                    async move {
-                                        let response = match response.await {
-                                            Ok(result) => Response {
-                                                jsonrpc: JSON_RPC_VERSION,
-                                                id,
-                                                value: LspResult::Ok(Some(result)),
-                                            },
-                                            Err(error) => Response {
-                                                jsonrpc: JSON_RPC_VERSION,
-                                                id,
-                                                value: LspResult::Error(Some(Error {
-                                                    message: error.to_string(),
-                                                })),
-                                            },
-                                        };
-                                        if let Some(response) =
-                                            serde_json::to_string(&response).log_err()
-                                        {
-                                            outbound_tx.try_send(response).ok();
-                                        }
-                                    }
-                                })
-                                .detach();
-                        }
+                    let f = f.clone();
+                    let deserialized_params = cx
+                        .background_executor()
+                        .spawn(async move { serde_json::from_value(params) });
 
-                        Err(error) => {
-                            log::error!("error deserializing {} request: {:?}", method, error);
-                            let response = AnyResponse {
-                                jsonrpc: JSON_RPC_VERSION,
-                                id,
-                                result: None,
-                                error: Some(Error {
-                                    message: error.to_string(),
-                                }),
-                            };
-                            if let Some(response) = serde_json::to_string(&response).log_err() {
-                                outbound_tx.try_send(response).ok();
+                    cx.spawn({
+                        let outbound_tx = outbound_tx.clone();
+                        move |cx| async move {
+                            match deserialized_params.await {
+                                Ok(params) => {
+                                    let response = f(params, cx.clone());
+                                    let response = match response.await {
+                                        Ok(result) => Response {
+                                            jsonrpc: JSON_RPC_VERSION,
+                                            id,
+                                            value: LspResult::Ok(Some(result)),
+                                        },
+                                        Err(error) => Response {
+                                            jsonrpc: JSON_RPC_VERSION,
+                                            id,
+                                            value: LspResult::Error(Some(Error {
+                                                message: error.to_string(),
+                                            })),
+                                        },
+                                    };
+                                    if let Some(response) =
+                                        serde_json::to_string(&response).log_err()
+                                    {
+                                        outbound_tx.try_send(response).ok();
+                                    }
+                                }
+                                Err(error) => {
+                                    log::error!(
+                                        "error deserializing {} request: {:?}",
+                                        method,
+                                        error
+                                    );
+                                    let response = AnyResponse {
+                                        jsonrpc: JSON_RPC_VERSION,
+                                        id,
+                                        result: None,
+                                        error: Some(Error {
+                                            message: error.to_string(),
+                                        }),
+                                    };
+                                    if let Some(response) =
+                                        serde_json::to_string(&response).log_err()
+                                    {
+                                        outbound_tx.try_send(response).ok();
+                                    }
+                                }
                             }
                         }
-                    }
+                    })
+                    .detach();
                 }
             }),
         );
@@ -1425,12 +1445,12 @@ impl FakeLanguageServer {
     /// Registers a handler for a specific kind of request. Removes any existing handler for specified request type.
     pub fn handle_request<T, F, Fut>(
         &self,
-        mut handler: F,
+        handler: F,
     ) -> futures::channel::mpsc::UnboundedReceiver<()>
     where
         T: 'static + request::Request,
         T::Params: 'static + Send,
-        F: 'static + Send + FnMut(T::Params, gpui::AsyncAppContext) -> Fut,
+        F: 'static + Send + Sync + Fn(T::Params, gpui::AsyncAppContext) -> Fut,
         Fut: 'static + Send + Future<Output = Result<T::Result>>,
     {
         let (responded_tx, responded_rx) = futures::channel::mpsc::unbounded();
@@ -1454,12 +1474,12 @@ impl FakeLanguageServer {
     /// Registers a handler for a specific kind of notification. Removes any existing handler for specified notification type.
     pub fn handle_notification<T, F>(
         &self,
-        mut handler: F,
+        handler: F,
     ) -> futures::channel::mpsc::UnboundedReceiver<()>
     where
         T: 'static + notification::Notification,
         T::Params: 'static + Send,
-        F: 'static + Send + FnMut(T::Params, gpui::AsyncAppContext),
+        F: 'static + Send + Sync + Fn(T::Params, gpui::AsyncAppContext),
     {
         let (handled_tx, handled_rx) = futures::channel::mpsc::unbounded();
         self.server.remove_notification_handler::<T>();