Index: clangd/ClangdLSPServer.h
===================================================================
--- clangd/ClangdLSPServer.h
+++ clangd/ClangdLSPServer.h
@@ -183,12 +183,10 @@
   // Store of the current versions of the open documents.
   DraftStore DraftMgr;
 
-  // Server must be the last member of the class to allow its destructor to exit
-  // the worker thread that may otherwise run an async callback on partially
-  // destructed instance of ClangdLSPServer.
-  // Set in construtor and destroyed when run() finishes. To ensure all worker
-  // threads exit before run() returns.
-  std::unique_ptr<ClangdServer> Server;
+  // The ClangdServer is created by the "initialize" LSP method.
+  // It is destroyed before run() returns, to ensure worker threads exit.
+  ClangdServer::Options ClangdServerOpts;
+  llvm::Optional<ClangdServer> Server;
 };
 } // namespace clangd
 } // namespace clang
Index: clangd/ClangdLSPServer.cpp
===================================================================
--- clangd/ClangdLSPServer.cpp
+++ clangd/ClangdLSPServer.cpp
@@ -87,6 +87,7 @@
 //  - logging of inbound messages
 //  - cancellation handling
 //  - basic call tracing
+// MessageHandler ensures that initialize() is called before any other handler.
 class ClangdLSPServer::MessageHandler : public Transport::MessageHandler {
 public:
   MessageHandler(ClangdLSPServer &Server) : Server(Server) {}
@@ -95,7 +96,9 @@
     log("<-- {0}", Method);
     if (Method == "exit")
       return false;
-    if (Method == "$/cancelRequest")
+    if (!Server.Server)
+      elog("Notification {0} before initialization", Method);
+    else if (Method == "$/cancelRequest")
       onCancel(std::move(Params));
     else if (auto Handler = Notifications.lookup(Method))
       Handler(std::move(Params));
@@ -106,7 +109,11 @@
 
   bool onCall(StringRef Method, json::Value Params, json::Value ID) override {
     log("<-- {0}({1})", Method, ID);
-    if (auto Handler = Calls.lookup(Method))
+    if (!Server.Server && Method != "initialize") {
+      elog("Call {0} before initialization.", Method);
+      Server.reply(ID, make_error<LSPError>("server not initialized",
+                                            ErrorCode::ServerNotInitialized));
+    } else if (auto Handler = Calls.lookup(Method))
       Handler(std::move(Params), std::move(ID));
     else
       Server.reply(ID, llvm::make_error<LSPError>("method not found",
@@ -254,6 +261,11 @@
 
 void ClangdLSPServer::onInitialize(const InitializeParams &Params,
                                    Callback<json::Value> Reply) {
+  if (Server)
+    return Reply(make_error<LSPError>("server already initialized",
+                                      ErrorCode::InvalidRequest));
+  Server.emplace(CDB.getCDB(), FSProvider,
+                 static_cast<DiagnosticsConsumer &>(*this), ClangdServerOpts);
   if (Params.initializationOptions) {
     const ClangdInitializationOptions &Opts = *Params.initializationOptions;
 
@@ -663,8 +675,7 @@
                                      std::move(CompileCommandsDir))),
       CCOpts(CCOpts), SupportedSymbolKinds(defaultSymbolKinds()),
       SupportedCompletionItemKinds(defaultCompletionItemKinds()),
-      Server(new ClangdServer(CDB.getCDB(), FSProvider, /*DiagConsumer=*/*this,
-                              Opts)) {
+      ClangdServerOpts(Opts) {
   // clang-format off
   MsgHandler->bind("initialize", &ClangdLSPServer::onInitialize);
   MsgHandler->bind("shutdown", &ClangdLSPServer::onShutdown);
@@ -694,8 +705,6 @@
 ClangdLSPServer::~ClangdLSPServer() = default;
 
 bool ClangdLSPServer::run() {
-  assert(Server);
-
   // Run the Language Server loop.
   bool CleanExit = true;
   if (auto Err = Transp.loop(*MsgHandler)) {
@@ -705,7 +714,6 @@
 
   // Destroy ClangdServer to ensure all worker threads finish.
   Server.reset();
-
   return CleanExit && ShutdownRequestReceived;
 }
 
Index: clangd/ClangdServer.h
===================================================================
--- clangd/ClangdServer.h
+++ clangd/ClangdServer.h
@@ -90,7 +90,7 @@
     /// defaults and -resource-dir compiler flag).
     /// If None, ClangdServer calls CompilerInvocation::GetResourcePath() to
     /// obtain the standard resource directory.
-    llvm::Optional<StringRef> ResourceDir = llvm::None;
+    llvm::Optional<std::string> ResourceDir = llvm::None;
 
     /// Time to wait after a new file version before computing diagnostics.
     std::chrono::steady_clock::duration UpdateDebounce =
Index: clangd/ClangdServer.cpp
===================================================================
--- clangd/ClangdServer.cpp
+++ clangd/ClangdServer.cpp
@@ -103,7 +103,7 @@
                            DiagnosticsConsumer &DiagConsumer,
                            const Options &Opts)
     : CDB(CDB), DiagConsumer(DiagConsumer), FSProvider(FSProvider),
-      ResourceDir(Opts.ResourceDir ? Opts.ResourceDir->str()
+      ResourceDir(Opts.ResourceDir ? *Opts.ResourceDir
                                    : getStandardResourceDir()),
       DynamicIdx(Opts.BuildDynamicSymbolIndex
                      ? new FileIndex(Opts.URISchemes,
Index: test/clangd/exit-with-shutdown.test
===================================================================
--- test/clangd/exit-with-shutdown.test
+++ test/clangd/exit-with-shutdown.test
@@ -1,4 +1,6 @@
 # RUN: clangd -lit-test < %s
+{"jsonrpc":"2.0","id":0,"method":"initialize","params":{"processId":123,"rootPath":"clangd","capabilities":{},"trace":"off"}}
+---
 {"jsonrpc":"2.0","id":3,"method":"shutdown"}
 ---
 {"jsonrpc":"2.0","method":"exit"}
Index: test/clangd/exit-without-shutdown.test
===================================================================
--- test/clangd/exit-without-shutdown.test
+++ test/clangd/exit-without-shutdown.test
@@ -1,2 +1,4 @@
 # RUN: not clangd -lit-test < %s
+{"jsonrpc":"2.0","id":0,"method":"initialize","params":{"processId":123,"rootPath":"clangd","capabilities":{},"trace":"off"}}
+---
 {"jsonrpc":"2.0","method":"exit"}
Index: test/clangd/initialize-sequence.test
===================================================================
--- /dev/null
+++ test/clangd/initialize-sequence.test
@@ -0,0 +1,21 @@
+# RUN: clangd -lit-test < %s | FileCheck -strict-whitespace %s
+{"jsonrpc":"2.0","id":0,"method":"workspace/symbol","params":{"query":"std::basic_ostringstream"}}
+#      CHECK:  "error": {
+# CHECK-NEXT:    "code": -32002
+# CHECK-NEXT:    "message": "server not initialized"
+# CHECK-NEXT:  },
+# CHECK-NEXT:  "id": 0,
+---
+{"jsonrpc":"2.0","id":1,"method":"initialize","params":{"processId":123,"rootPath":"clangd","capabilities":{},"trace":"off"}}
+---
+{"jsonrpc":"2.0","id":2,"method":"initialize","params":{"processId":123,"rootPath":"clangd","capabilities":{},"trace":"off"}}
+#      CHECK:  "error": {
+# CHECK-NEXT:    "code": -32600
+# CHECK-NEXT:    "message": "server already initialized"
+# CHECK-NEXT:  },
+# CHECK-NEXT:  "id": 2,
+---
+{"jsonrpc":"2.0","id":3,"method":"shutdown"}
+---
+{"jsonrpc":"2.0","method":"exit"}
+