perf: Request cancellation while processing changed files

Author: Veykril

crates/rust-analyzer/src/global_state.rs

@@ -290,21 +290,25 @@ impl GlobalState {
 
     pub(crate) fn process_changes(&mut self) -> bool {
         let _p = span!(Level::INFO, "GlobalState::process_changes").entered();
-
         // We cannot directly resolve a change in a ratoml file to a format
         // that can be used by the config module because config talks
         // in `SourceRootId`s instead of `FileId`s and `FileId` -> `SourceRootId`
         // mapping is not ready until `AnalysisHost::apply_changes` has been called.
         let mut modified_ratoml_files: FxHashMap<FileId, (ChangeKind, vfs::VfsPath)> =
             FxHashMap::default();
 
-        let (change, modified_rust_files, workspace_structure_change) = {
-            let mut change = ChangeWithProcMacros::default();
-            let mut guard = self.vfs.write();
-            let changed_files = guard.0.take_changes();
-            if changed_files.is_empty() {
-                return false;
-            }
+        let mut change = ChangeWithProcMacros::default();
+        let mut guard = self.vfs.write();
+        let changed_files = guard.0.take_changes();
+        if changed_files.is_empty() {
+            return false;
+        }
+
+        let (change, modified_rust_files, workspace_structure_change) = std::thread::scope(|s| {
+            // start cancellation in parallel, this will kick off lru eviction
+            // allowing us to do meaningful work while waiting
+            // FIXME: We should have a long living thread for this purpose instead of re-spawning.
+            s.spawn(|| self.analysis_host.request_cancellation());
 
             // downgrade to read lock to allow more readers while we are normalizing text
             let guard = RwLockWriteGuard::downgrade_to_upgradable(guard);
@@ -387,9 +391,8 @@ impl GlobalState {
                 change.set_roots(roots);
             }
             (change, modified_rust_files, workspace_structure_change)
-        };
+        });
 
-        let _p = span!(Level::INFO, "GlobalState::process_changes/apply_change").entered();
         self.analysis_host.apply_change(change);
         if !modified_ratoml_files.is_empty()
             || !self.config.same_source_root_parent_map(&self.local_roots_parent_map)