From 5c410385fc2780238864e3e090fc4cff37b5c3fb Mon Sep 17 00:00:00 2001
From: Aleksey Kladov <aleksey.kladov@gmail.com>
Date: Wed, 29 May 2019 16:05:14 +0300
Subject: optimization: cancel backlog in onEnter

---
 crates/ra_lsp_server/src/main_loop.rs    | 15 ++++++++++++---
 crates/ra_lsp_server/src/server_world.rs |  4 ++++
 2 files changed, 16 insertions(+), 3 deletions(-)

diff --git a/crates/ra_lsp_server/src/main_loop.rs b/crates/ra_lsp_server/src/main_loop.rs
index e65bb0972..d29ba94e7 100644
--- a/crates/ra_lsp_server/src/main_loop.rs
+++ b/crates/ra_lsp_server/src/main_loop.rs
@@ -1,7 +1,7 @@
 mod handlers;
 mod subscriptions;
 
-use std::{fmt, path::PathBuf, sync::Arc, time::Instant};
+use std::{fmt, path::PathBuf, sync::Arc, time::Instant, any::TypeId};
 
 use crossbeam_channel::{select, unbounded, Receiver, RecvError, Sender};
 use failure::{bail, format_err};
@@ -447,14 +447,14 @@ struct PoolDispatcher<'a> {
     req: Option<RawRequest>,
     res: Option<u64>,
     pool: &'a ThreadPool,
-    world: &'a ServerWorldState,
+    world: &'a mut ServerWorldState,
     sender: &'a Sender<Task>,
 }
 
 impl<'a> PoolDispatcher<'a> {
     fn on<R>(&mut self, f: fn(ServerWorld, R::Params) -> Result<R::Result>) -> Result<&mut Self>
     where
-        R: req::Request,
+        R: req::Request + 'static,
         R::Params: DeserializeOwned + Send + 'static,
         R::Result: Serialize + 'static,
     {
@@ -464,6 +464,15 @@ impl<'a> PoolDispatcher<'a> {
         };
         match req.cast::<R>() {
             Ok((id, params)) => {
+                // Real time requests block user typing, so we should react quickly to them.
+                // Currently this means that we try to cancel background jobs if we don't have
+                // a spare thread.
+                let is_real_time = TypeId::of::<R>() == TypeId::of::<req::JoinLines>()
+                    || TypeId::of::<R>() == TypeId::of::<req::OnEnter>();
+                if self.pool.queued_count() > 0 && is_real_time {
+                    self.world.cancel_requests();
+                }
+
                 let world = self.world.snapshot();
                 let sender = self.sender.clone();
                 self.pool.execute(move || {
diff --git a/crates/ra_lsp_server/src/server_world.rs b/crates/ra_lsp_server/src/server_world.rs
index b63927a4f..7eb4d3e56 100644
--- a/crates/ra_lsp_server/src/server_world.rs
+++ b/crates/ra_lsp_server/src/server_world.rs
@@ -149,6 +149,10 @@ impl ServerWorldState {
         self.analysis_host.apply_change(change);
     }
 
+    pub fn cancel_requests(&mut self) {
+        self.analysis_host.apply_change(AnalysisChange::new());
+    }
+
     pub fn snapshot(&self) -> ServerWorld {
         ServerWorld {
             workspaces: Arc::clone(&self.workspaces),
-- 
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