[clangd] Make sure ReplyCallbacks are destroyed before RequestCancelersMutex

Summary:
After rL374163, replycallbacks might have a cancellable context, which
will try to access RequestCancellers on destruction. See
http://45.33.8.238/mac/1245/step_7.txt for a sample failure.

Reviewers: sammccall

Subscribers: ilya-biryukov, MaskRay, jkorous, arphaman, usaxena95, cfe-commits, thakis

Tags: #clang

Differential Revision: https://reviews.llvm.org/D68702

llvm-svn: 374168

Author: kadircet

clang-tools-extra/clangd/ClangdLSPServer.cpp

@@ -371,16 +371,6 @@ class ClangdLSPServer::MessageHandler : public Transport::MessageHandler {
 
   llvm::StringMap<std::function<void(llvm::json::Value)>> Notifications;
   llvm::StringMap<std::function<void(llvm::json::Value, ReplyOnce)>> Calls;
-  // The maximum number of callbacks held in clangd.
-  //
-  // We bound the maximum size to the pending map to prevent memory leakage
-  // for cases where LSP clients don't reply for the request.
-  static constexpr int MaxReplayCallbacks = 100;
-  mutable std::mutex CallMutex;
-  int NextCallID = 0; /* GUARDED_BY(CallMutex) */
-  std::deque<std::pair</*RequestID*/ int,
-                       /*ReplyHandler*/ Callback<llvm::json::Value>>>
-      ReplyCallbacks; /* GUARDED_BY(CallMutex) */
 
   // Method calls may be cancelled by ID, so keep track of their state.
   // This needs a mutex: handlers may finish on a different thread, and that's
@@ -432,6 +422,19 @@ class ClangdLSPServer::MessageHandler : public Transport::MessageHandler {
     }));
   }
 
+  // The maximum number of callbacks held in clangd.
+  //
+  // We bound the maximum size to the pending map to prevent memory leakage
+  // for cases where LSP clients don't reply for the request.
+  // This has to go after RequestCancellers and RequestCancellersMutex since it
+  // can contain a callback that has a cancelable context.
+  static constexpr int MaxReplayCallbacks = 100;
+  mutable std::mutex CallMutex;
+  int NextCallID = 0; /* GUARDED_BY(CallMutex) */
+  std::deque<std::pair</*RequestID*/ int,
+                       /*ReplyHandler*/ Callback<llvm::json::Value>>>
+      ReplyCallbacks; /* GUARDED_BY(CallMutex) */
+
   ClangdLSPServer &Server;
 };
 constexpr int ClangdLSPServer::MessageHandler::MaxReplayCallbacks;