Merge pull request #159 from wravery/wraptype-shared-mutex

Fix #158

Author: wravery

include/graphqlservice/GraphQLSchema.h

@@ -9,6 +9,7 @@
 #include "graphqlservice/GraphQLService.h"
 
 #include <initializer_list>
+#include <shared_mutex>
 
 namespace graphql {
 namespace introspection {
@@ -70,8 +71,10 @@ class Schema : public std::enable_shared_from_this<Schema>
 	internal::string_view_map<size_t> _typeMap;
 	std::vector<std::pair<std::string_view, std::shared_ptr<const BaseType>>> _types;
 	std::vector<std::shared_ptr<const Directive>> _directives;
+	std::shared_mutex _nonNullWrappersMutex;
 	internal::sorted_map<std::shared_ptr<const BaseType>, std::shared_ptr<const BaseType>>
 		_nonNullWrappers;
+	std::shared_mutex _listWrappersMutex;
 	internal::sorted_map<std::shared_ptr<const BaseType>, std::shared_ptr<const BaseType>>
 		_listWrappers;
 };

src/GraphQLSchema.cpp

@@ -64,10 +64,18 @@ std::shared_ptr<const BaseType> Schema::WrapType(
 	introspection::TypeKind kind, std::shared_ptr<const BaseType> ofType)
 {
 	auto& wrappers = (kind == introspection::TypeKind::LIST) ? _listWrappers : _nonNullWrappers;
+	auto& mutex =
+		(kind == introspection::TypeKind::LIST) ? _listWrappersMutex : _nonNullWrappersMutex;
+	std::shared_lock shared_lock { mutex };
+	std::unique_lock unique_lock { mutex, std::defer_lock };
 	auto itr = wrappers.find(ofType);
 
 	if (itr == wrappers.end())
 	{
+		// Trade the shared_lock for a unique_lock.
+		shared_lock.unlock();
+		unique_lock.lock();
+
 		std::tie(itr, std::ignore) = wrappers.emplace(ofType, WrapperType::Make(kind, ofType));
 	}