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DEV: a shared resource utility added

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/*!
* \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__ */

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