DEV: a shared resource utility added

include/utl/utility/shared.h

@@ -0,0 +1,106 @@
+/*!
+ * \file utility/shared.h
+ * \brief
+ *      A CRTP base class to provide acquire/release functionality for shared resources
+ *      without handle pointers.
+ *
+ * \copyright Copyright (C) 2021 Christos Choutouridis <christos@choutouridis.net>
+ *
+ * <dl class=\"section copyright\"><dt>License</dt><dd>
+ * The MIT License (MIT)
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ * </dd></dl>
+ */
+
+#ifndef utl_utility_shared_h__
+#define utl_utility_shared_h__
+
+#include <utl/core/impl.h>
+
+#include <utility>
+
+namespace utl {
+
+/*!
+ * A CRTP base class to provide acquire/release functionality for shared resources
+ * without handle pointers.
+ *
+ * \example
+ * \code
+ * class GPIOClock : public shared<GPIOClock> {
+ *     friend shared<GPIOClock>;
+ *     void acquire_impl() { // HAL enable gpio clock }
+ *     void release_impl() { // HAL disable gpio clock }
+ * };
+ * GPIOClock clk;
+ * class Pin {
+ *     Pin() {
+ *         clk.acquire();
+ *         // init pin
+ *     }
+ *     ~Pin() {
+ *         // de-init pin
+ *         clk.release();
+ *     }
+ * };
+ * \endcode
+ *
+ * \tparam Impl_t   The derived class type
+ */
+template <typename Impl_t>
+class shared {
+        _CRTP_IMPL(Impl_t);
+        int count {};   //!< acquisition counter
+
+    protected:
+        shared() noexcept               = default;
+        shared(const shared&)           = delete;   //!< No copies
+        shared operator=(const shared&) = delete;   //!< No copies
+
+    public:
+        /*!
+         * Acquires the recourse. If it is the first call to acquire the resource we actually acquire it.
+         * Otherwise we just keep track of how many acquisition have made.
+         *
+         * \tparam Ts   The types of possible arguments
+         * \param args  Possible arguments to pass to acquire_impl() of derived class
+         */
+        template <typename ...Ts>
+        void acquire (Ts&&... args) {
+            if (!count++)   impl().acquire_impl(std::forward<Ts>(args)...);
+        }
+        /*!
+         * Release the recourse. On every call we decrease the count of acquisitions. If we reach zero
+         * we actually release the resource.
+         *
+         * \tparam Ts   The types of possible arguments
+         * \param args  Possible arguments to pass to release_impl() of derived class
+         */
+        template <typename ...Ts>
+        void release (Ts&&... args) noexcept {
+            if (--count <= 0) {
+                impl().release_impl(std::forward<Ts>(args)...);
+                count =0;
+            }
+        }
+};
+
+} // namespace utl;
+#endif /* utl_utility_shared_h__ */