From 063916d70f794f4b30365d927408388295eb7053 Mon Sep 17 00:00:00 2001
From: Bernhard Manfred Gruber <bernhardmgruber@gmail.com>
Date: Fri, 15 Sep 2023 21:17:18 +0200
Subject: [PATCH] Add Locked accessor

This accessor protects each data access using a mutex.
---
 include/llama/Accessors.hpp | 55 +++++++++++++++++++++++++++++++++++++
 include/llama/View.hpp      |  2 +-
 tests/accessor.cpp          | 17 ++++++++++++
 3 files changed, 73 insertions(+), 1 deletion(-)

diff --git a/include/llama/Accessors.hpp b/include/llama/Accessors.hpp
index b35df09212..671f9f27b0 100644
--- a/include/llama/Accessors.hpp
+++ b/include/llama/Accessors.hpp
@@ -8,6 +8,8 @@
 #include "macros.hpp"
 
 #include <atomic>
+#include <memory>
+#include <mutex>
 
 namespace llama::accessor
 {
@@ -112,6 +114,59 @@ namespace llama::accessor
     };
 #endif
 
+    /// Locks a mutex during each access to the data structure.
+    template<typename Mutex = std::mutex>
+    struct Locked
+    {
+        // mutexes are usually not movable, so we put them on the heap, so the accessor is movable
+        std::unique_ptr<Mutex> m = std::make_unique<Mutex>();
+
+        template<typename Ref, typename Value>
+        // NOLINTNEXTLINE(cppcoreguidelines-special-member-functions,hicpp-special-member-functions)
+        struct Reference : ProxyRefOpMixin<Reference<Ref, Value>, Value>
+        {
+            Ref ref;
+            Mutex& m;
+
+            using value_type = Value;
+
+            // NOLINTNEXTLINE(bugprone-unhandled-self-assignment,cert-oop54-cpp)
+            LLAMA_FORCE_INLINE constexpr auto operator=(const Reference& other) -> Reference&
+            {
+                const std::lock_guard<Mutex> lock(m);
+                *this = static_cast<value_type>(other);
+                return *this;
+            }
+
+            // NOLINTNEXTLINE(google-explicit-constructor,hicpp-explicit-conversions)
+            LLAMA_FORCE_INLINE operator value_type() const
+            {
+                const std::lock_guard<Mutex> lock(m);
+                return static_cast<value_type>(ref);
+            }
+
+            template<typename T>
+            LLAMA_FORCE_INLINE auto operator=(T t) -> Reference&
+            {
+                const std::lock_guard<Mutex> lock(m);
+                ref = t;
+                return *this;
+            }
+        };
+
+        template<typename PR>
+        LLAMA_FORCE_INLINE auto operator()(PR r) const -> Reference<PR, typename PR::value_type>
+        {
+            return {{}, r, *m};
+        }
+
+        template<typename T>
+        LLAMA_FORCE_INLINE auto operator()(T& r) const -> Reference<T&, std::remove_cv_t<T>>
+        {
+            return {{}, r, *m};
+        }
+    };
+
     namespace internal
     {
         template<std::size_t I, typename Accessor>
diff --git a/include/llama/View.hpp b/include/llama/View.hpp
index fe2eb83b34..8f0661acf8 100644
--- a/include/llama/View.hpp
+++ b/include/llama/View.hpp
@@ -151,7 +151,7 @@ namespace llama
     LLAMA_FN_HOST_ACC_INLINE auto allocView(Mapping mapping = {}, const Allocator& alloc = {}, Accessor accessor = {})
         -> View<Mapping, internal::AllocatorBlobType<Allocator, typename Mapping::RecordDim>, Accessor>
     {
-        auto view = allocViewUninitialized(std::move(mapping), alloc, accessor);
+        auto view = allocViewUninitialized(std::move(mapping), alloc, std::move(accessor));
         constructFields(view);
         return view;
     }
diff --git a/tests/accessor.cpp b/tests/accessor.cpp
index ce0efa1efe..38928f9b60 100644
--- a/tests/accessor.cpp
+++ b/tests/accessor.cpp
@@ -3,6 +3,8 @@
 
 #include "common.hpp"
 
+#include <thread>
+
 TEST_CASE("view.allocView.Default")
 {
     auto mapping = llama::mapping::AoS{llama::ArrayExtents{3, 4}, Particle{}};
@@ -36,6 +38,21 @@ TEST_CASE("view.allocView.Atomic")
 }
 #endif
 
+TEST_CASE("view.allocView.Locked")
+{
+    auto mapping = llama::mapping::AoS{llama::ArrayExtents{3, 4}, Vec3I{}};
+    auto view = llama::allocView(mapping, llama::bloballoc::Vector{}, llama::accessor::Locked{});
+    iotaFillView(view);
+    iotaCheckView(view);
+    // concurrent access. TSAN would detect a race here (e.g. with Default accessor, tested with clang-16).
+    std::thread t1{[&] { view(1, 1)(tag::X{}) = 1; }};
+    std::thread t2{[&] { view(1, 1)(tag::X{}) = 2; }};
+    std::thread t3{[&] { view(2, 2)(tag::X{}) = 3; }};
+    t1.join();
+    t2.join();
+    t3.join();
+}
+
 TEST_CASE("view.withAccessor.Default.Vector")
 {
     auto view