Index: clang-tools-extra/trunk/clangd/ClangdServer.h
===================================================================
--- clang-tools-extra/trunk/clangd/ClangdServer.h
+++ clang-tools-extra/trunk/clangd/ClangdServer.h
@@ -12,6 +12,7 @@
 
 #include "ClangdUnit.h"
 #include "CodeComplete.h"
+#include "FSProvider.h"
 #include "Function.h"
 #include "GlobalCompilationDatabase.h"
 #include "Protocol.h"
@@ -42,22 +43,6 @@
                                   std::vector<Diag> Diagnostics) = 0;
 };
 
-class FileSystemProvider {
-public:
-  virtual ~FileSystemProvider() = default;
-  /// Called by ClangdServer to obtain a vfs::FileSystem to be used for parsing.
-  /// Context::current() will be the context passed to the clang entrypoint,
-  /// such as addDocument(), and will also be propagated to result callbacks.
-  /// Embedders may use this to isolate filesystem accesses.
-  virtual IntrusiveRefCntPtr<vfs::FileSystem> getFileSystem() = 0;
-};
-
-class RealFileSystemProvider : public FileSystemProvider {
-public:
-  /// Returns getRealFileSystem().
-  IntrusiveRefCntPtr<vfs::FileSystem> getFileSystem() override;
-};
-
 /// Provides API to manage ASTs for a collection of C++ files and request
 /// various language features.
 /// Currently supports async diagnostics, code completion, formatting and goto
Index: clang-tools-extra/trunk/clangd/ClangdServer.cpp
===================================================================
--- clang-tools-extra/trunk/clangd/ClangdServer.cpp
+++ clang-tools-extra/trunk/clangd/ClangdServer.cpp
@@ -68,10 +68,6 @@
 
 } // namespace
 
-IntrusiveRefCntPtr<vfs::FileSystem> RealFileSystemProvider::getFileSystem() {
-  return vfs::getRealFileSystem();
-}
-
 ClangdServer::Options ClangdServer::optsForTest() {
   ClangdServer::Options Opts;
   Opts.UpdateDebounce = std::chrono::steady_clock::duration::zero(); // Faster!
Index: clang-tools-extra/trunk/clangd/FSProvider.h
===================================================================
--- clang-tools-extra/trunk/clangd/FSProvider.h
+++ clang-tools-extra/trunk/clangd/FSProvider.h
@@ -0,0 +1,42 @@
+//===--- FSProvider.h - VFS provider for ClangdServer ------------*- C++-*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CLANG_TOOLS_EXTRA_CLANGD_FSPROVIDER_H
+#define LLVM_CLANG_TOOLS_EXTRA_CLANGD_FSPROVIDER_H
+
+#include "clang/Basic/VirtualFileSystem.h"
+#include "llvm/ADT/IntrusiveRefCntPtr.h"
+
+namespace clang {
+namespace clangd {
+
+// Wrapper for vfs::FileSystem for use in multithreaded programs like clangd.
+// As FileSystem is not threadsafe, concurrent threads must each obtain one.
+class FileSystemProvider {
+public:
+  virtual ~FileSystemProvider() = default;
+  /// Called by ClangdServer to obtain a vfs::FileSystem to be used for parsing.
+  /// Context::current() will be the context passed to the clang entrypoint,
+  /// such as addDocument(), and will also be propagated to result callbacks.
+  /// Embedders may use this to isolate filesystem accesses.
+  virtual IntrusiveRefCntPtr<vfs::FileSystem> getFileSystem() = 0;
+};
+
+class RealFileSystemProvider : public FileSystemProvider {
+public:
+  // FIXME: returns the single real FS instance, which is not threadsafe.
+  IntrusiveRefCntPtr<vfs::FileSystem> getFileSystem() override {
+    return vfs::getRealFileSystem();
+  }
+};
+
+} // namespace clangd
+} // namespace clang
+
+#endif