Implement Atomic Forward List

An implementation of a singly-linked list with atomic access to allow for lock-free access semantics, it eliminates the requirement for a mutex which can introduce additional consideration for synchronization.

app/src/main/cpp/skyline/common/atomic_forward_list.h

@@ -0,0 +1,110 @@
+// SPDX-License-Identifier: MPL-2.0
+// Copyright © 2022 Skyline Team and Contributors (https://github.com/skyline-emu/)
+
+#pragma once
+
+#include <atomic>
+
+namespace skyline {
+    /**
+     * @brief A singly-linked list with atomic access to allow for lock-free access semantics
+     */
+    template<typename Type>
+    class AtomicForwardList {
+      private:
+        struct Node {
+            Node *next;
+            Type value;
+        };
+
+        std::atomic<Node *> head{}; //!< The head of the list
+
+      public:
+        AtomicForwardList() = default;
+
+        AtomicForwardList(const AtomicForwardList &) = delete;
+
+        AtomicForwardList(AtomicForwardList &&other) {
+            head = other.head.load();
+            while (!other.head.compare_exchange_strong(head, nullptr, std::memory_order_release, std::memory_order_consume));
+        }
+
+        ~AtomicForwardList() {
+            Clear();
+        }
+
+        /**
+         * @brief Clears all the items from the list while deallocating them
+         */
+        void Clear() {
+            auto current{head.exchange(nullptr, std::memory_order_acquire)};
+            while (current) {
+                auto next{current->next};
+                delete current;
+                current = next;
+            }
+        }
+
+        /**
+         * @brief Appends an item to the start of the list
+         */
+        void Append(Type item) {
+            auto node{new Node{nullptr, item}};
+            auto next{head.load(std::memory_order_consume)};
+            do {
+                node->next = next;
+            } while (!head.compare_exchange_strong(next, node, std::memory_order_release, std::memory_order_consume));
+        }
+
+        /**
+         * @brief Appends multiple items to the start of the list
+         */
+        void Append(std::initializer_list<Type> items) {
+            if (std::empty(items))
+                return;
+
+            Node* firstNode{new Node{nullptr, *items.begin()}};
+            Node* lastNode{firstNode};
+            for (auto item{items.begin() + 1}; item != items.end(); item++)
+                lastNode = new Node{lastNode, *item};
+
+            auto next{head.load(std::memory_order_consume)};
+            do {
+                firstNode->next = next;
+            } while (!head.compare_exchange_strong(next, lastNode, std::memory_order_release, std::memory_order_consume));
+        }
+
+        template<typename... Items>
+        void Append(Items &&... items) {
+            Append(std::initializer_list<Type>{std::forward<Items>(items)...});
+        }
+
+        /**
+         * @brief Iterates over every single list item and calls the given function
+         * @note This function is **not** thread-safe when used with Clear() as the item may be deallocated while iterating
+         */
+        template <typename Function>
+        void Iterate(Function function) {
+            auto current{head.load(std::memory_order_consume)};
+            while (current) {
+                function(current->value);
+                current = current->next;
+            }
+        }
+
+        /**
+         * @brief Iterates over every single list item and calls the given function till the given predicate returns false
+         * @note This function is **not** thread-safe when used with Clear() as the item may be deallocated while iterating
+         */
+        template <typename Function>
+        bool AllOf(Function function) {
+            auto current{head.load(std::memory_order_consume)};
+            while (current) {
+                if (!function(current->value))
+                    return false;
+                current = current->next;
+            }
+            return true;
+        }
+    };
+}