Disposer.hpp

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// The Reactive C++ Toolbox.
// Copyright (C) 2013-2019 Swirly Cloud Limited
// Copyright (C) 2021 Reactive Markets Limited
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
 
#ifndef TOOLBOX_IO_DISPOSER_HPP
#define TOOLBOX_IO_DISPOSER_HPP
 
#include <toolbox/sys/Time.hpp>
#include <toolbox/util/Finally.hpp>
 
namespace toolbox {
inline namespace io {
 
template <typename DerivedT>
class BasicDisposer {
  public:
    BasicDisposer() noexcept = default;
 
    // Copy.
    BasicDisposer(const BasicDisposer&) = delete;
    BasicDisposer& operator=(const BasicDisposer&) = delete;
 
    // Move.
    BasicDisposer(BasicDisposer&&) = delete;
    BasicDisposer& operator=(BasicDisposer&&) = delete;
 
    void dispose(CyclTime now) noexcept
    {
        if (locks_ == 0) {
            // Prevent the object from being disposed a second time by holding a lock
            // indefinitely.
            locks_ = 1;
            static_cast<DerivedT*>(this)->dispose_now(now);
        } else {
            dispose_ = true;
        }
    }
 
  protected:
    ~BasicDisposer() = default;
 
    bool is_locked() const noexcept { return locks_ > 0; }
 
    [[nodiscard]] auto lock_this(CyclTime now) noexcept
    {
        ++locks_;
        return make_finally([this, now]() noexcept {
            if (--locks_ == 0 && dispose_) {
                // Prevent the object from being disposed a second time by holding a lock
                // indefinitely.
                locks_ = 1;
                static_cast<DerivedT*>(this)->dispose_now(now);
            }
        });
    }
 
  private:
    short locks_{0};
    bool dispose_{false};
};
 
} // namespace io
} // namespace toolbox
 
#endif // TOOLBOX_IO_DISPOSER_HPP