Dispatch messages on the background (#54)

Author: rockbruno

Sources/SourceKitBazelBSP/Server/MessageHandler/AsyncMessageHandler.swift

@@ -0,0 +1,51 @@
+// Copyright (c) 2025 Spotify AB.
+//
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+import BuildServerProtocol
+import Foundation
+import LanguageServerProtocol
+
+/// Base object that forwards BSP messages to a separate queue.
+/// This exists simply to make sure we can continue to receive messages
+/// as we process them. Otherwise, each request would require its own queue.
+final class AsyncMessageHandler: MessageHandler {
+
+    private let queue = DispatchQueue(label: "AsyncMessageHandler", qos: .userInitiated)
+    private let messageHandler: MessageHandler
+
+    init(wrapping handler: MessageHandler) {
+        self.messageHandler = handler
+    }
+
+    func handle<Notification: NotificationType>(_ notification: Notification) {
+        queue.async { [weak self] in
+            self?.messageHandler.handle(notification)
+        }
+    }
+
+    func handle<Request: RequestType>(
+        _ request: Request,
+        id: RequestID,
+        reply: @escaping @Sendable (LSPResult<Request.Response>) -> Void
+    ) {
+        queue.async { [weak self] in
+            self?.messageHandler.handle(request, id: id, reply: reply)
+        }
+    }
+}

Sources/SourceKitBazelBSP/Server/SourceKitBazelBSPServer.swift

@@ -115,7 +115,10 @@ package final class SourceKitBazelBSPServer {
             outFD: outputHandle
         )
         let handler = Self.makeBSPMessageHandler(baseConfig: baseConfig, connection: connection)
-        self.init(connection: connection, handler: handler)
+        self.init(
+            connection: connection,
+            handler: AsyncMessageHandler(wrapping: handler)
+        )
     }
 
     package init(connection: LSPConnection, handler: MessageHandler) {