src: add ExclusiveAccess class

Similar to Rust's `std::sync::Mutex` in that it requires one to unwrap the object before accessing it, acquiring the mutex in the process. PR-URL: #31717 Reviewed-By: James M Snell <[email protected]> Reviewed-By: Colin Ihrig <[email protected]> Reviewed-By: Anna Henningsen <[email protected]> Reviewed-By: Tobias Nießen <[email protected]> Reviewed-By: David Carlier <[email protected]>

Author: bnoordhuis

src/node_mutex.h

@@ -6,6 +6,9 @@
 #include"util.h"
 #include"uv.h"
 
+#include<memory>// std::shared_ptr<T>
+#include<utility>// std::forward<T>
+
 namespacenode{
 
 template <typename Traits> classConditionVariableBase;
@@ -15,6 +18,51 @@ struct LibuvMutexTraits;
 using ConditionVariable = ConditionVariableBase<LibuvMutexTraits>
 using Mutex = MutexBase<LibuvMutexTraits>
 
+template <typename T, typename MutexT = Mutex>
+classExclusiveAccess{
+public:
+ExclusiveAccess() = default;
+
+template <typename... Args>
+explicitExclusiveAccess(Args&&... args)
+ : item_(std::forward<Args>(args)...){}
+
+ExclusiveAccess(const ExclusiveAccess&) = delete;
+ ExclusiveAccess& operator=(const ExclusiveAccess&) = delete;
+
+classScoped{
+public:
+// ExclusiveAccess will commonly be used in conjuction with std::shared_ptr
+// and without this constructor it's too easy to forget to keep a reference
+// around to the shared_ptr while operating on the ExclusiveAccess object.
+explicitScoped(const std::shared_ptr<ExclusiveAccess>& shared)
+ : shared_(shared)
+ , scoped_lock_(shared->mutex_)
+ , pointer_(&shared->item_){}
+
+explicitScoped(ExclusiveAccess* exclusive_access)
+ : shared_()
+ , scoped_lock_(exclusive_access->mutex_)
+ , pointer_(&exclusive_access->item_){}
+
+ T& operator*() const{return *pointer_}
+ T* operator->() const{return pointer_}
+
+Scoped(const Scoped&) = delete;
+ Scoped& operator=(const Scoped&) = delete;
+
+private:
+ std::shared_ptr<ExclusiveAccess> shared_;
+typename MutexT::ScopedLock scoped_lock_;
+ T* const pointer_;
+ };
+
+private:
+friendclassScopedLock;
+ MutexT mutex_;
+ T item_;
+};
+
 template <typename Traits>
 classMutexBase{
 public: