static_lifetime_guard.hpp

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// Copyright (c) 2023 by Apex.AI Inc. All rights reserved.
// Copyright (c) 2025 Contributors to the Eclipse Foundation
//
// See the NOTICE file(s) distributed with this work for additional
// information regarding copyright ownership.
//
// This program and the accompanying materials are made available under the
// terms of the Apache Software License 2.0 which is available at
// https://www.apache.org/licenses/LICENSE-2.0, or the MIT license
// which is available at https://opensource.org/licenses/MIT.
//
// SPDX-License-Identifier: Apache-2.0 OR MIT
 
#ifndef IOX2_BB_DESIGN_STATIC_LIFETIME_GUARD_HPP
#define IOX2_BB_DESIGN_STATIC_LIFETIME_GUARD_HPP
 
#include "iox2/legacy/atomic.hpp"
 
#include <type_traits>
#include <utility>
 
namespace iox2 {
namespace legacy {
template <typename T>
class StaticLifetimeGuard {
  public:
    StaticLifetimeGuard() noexcept;
 
    StaticLifetimeGuard(const StaticLifetimeGuard&) noexcept;
 
    StaticLifetimeGuard(StaticLifetimeGuard&&) noexcept;
 
    ~StaticLifetimeGuard() noexcept;
 
    // assignment does nothing since the objects have no state,
    // copy and move exist to support passing/returning a value object
    StaticLifetimeGuard& operator=(const StaticLifetimeGuard&) noexcept = default;
    StaticLifetimeGuard& operator=(StaticLifetimeGuard&&) noexcept = default;
 
    template <typename... Args>
    static T& instance(Args&&... args) noexcept;
 
    static uint64_t count();
 
  private:
    struct alignas(T) storage_t {
        // AXIVION Next Construct AutosarC++19_03-M0.1.3 : the field is intentionally unused and serves as a mean to provide memory
        // AXIVION Next Construct AutosarC++19_03-A1.1.1 : object size depends on template parameter and has to be taken care of at the specific template instantiation
        // AXIVION Next Construct AutosarC++19_03-A18.1.1 : required as low level building block, encapsulated in abstraction and not directly used
        // NOLINTNEXTLINE(hicpp-avoid-c-arrays, cppcoreguidelines-avoid-c-arrays)
        unsigned char data[sizeof(T)];
    };
 
    static constexpr uint32_t UNINITIALIZED { 0 };
    static constexpr uint32_t INITALIZING { 1 };
    static constexpr uint32_t INITALIZED { 2 };
 
    // NOLINTJUSTIFICATION these static variables are private and mutability is required
    // NOLINTBEGIN (cppcoreguidelines-avoid-non-const-global-variables)
    static storage_t s_storage;
    static concurrent::Atomic<uint64_t> s_count;
    static concurrent::Atomic<uint32_t> s_instanceState;
    static T* s_instance;
    // NOLINTEND (cppcoreguidelines-avoid-non-const-global-variables)
 
    static void destroy();
 
  protected:
    static uint64_t setCount(uint64_t count);
};
 
} // namespace legacy
} // namespace iox2
 
#include "iox2/legacy/detail/static_lifetime_guard.inl"
 
#endif // IOX2_BB_DESIGN_STATIC_LIFETIME_GUARD_HPP