shared_mem_object.h

/* SPDX-License-Identifier: LGPL-2.1-or-later */
/*
 * Copyright (C) 2023 Raspberry Pi Ltd
 * Copyright (C) 2024 Andrei Konovalov
 * Copyright (C) 2024 Dennis Bonke
 *
 * Helpers for shared memory allocations
 */
#pragma once

#include <stddef.h>
#include <stdint.h>
#include <string>
#include <sys/mman.h>
#include <type_traits>
#include <utility>

#include <libcamera/base/class.h>
#include <libcamera/base/shared_fd.h>
#include <libcamera/base/span.h>

namespace libcamera {

class SharedMem
{
public:
    SharedMem();

    SharedMem(const std::string &name, std::size_t size);
    SharedMem(SharedMem &&rhs);

    virtual ~SharedMem();

    SharedMem &operator=(SharedMem &&rhs);

    const SharedFD &fd() const
    {
        return fd_;
    }

    Span<uint8_t> mem() const
    {
        return mem_;
    }

    explicit operator bool() const
    {
        return !mem_.empty();
    }

private:
    LIBCAMERA_DISABLE_COPY(SharedMem)

    SharedFD fd_;

    Span<uint8_t> mem_;
};

template<class T, typename = std::enable_if_t<std::is_standard_layout<T>::value>>
class SharedMemObject : public SharedMem
{
public:
    static constexpr std::size_t kSize = sizeof(T);

    SharedMemObject()
        : SharedMem(), obj_(nullptr)
    {
    }

    template<class... Args>
    SharedMemObject(const std::string &name, Args &&...args)
        : SharedMem(name, kSize), obj_(nullptr)
    {
        if (mem().empty())
            return;

        obj_ = new (mem().data()) T(std::forward<Args>(args)...);
    }

    SharedMemObject(SharedMemObject<T> &&rhs)
        : SharedMem(std::move(rhs))
    {
        this->obj_ = rhs.obj_;
        rhs.obj_ = nullptr;
    }

    ~SharedMemObject()
    {
        if (obj_)
            obj_->~T();
    }

    SharedMemObject<T> &operator=(SharedMemObject<T> &&rhs)
    {
        SharedMem::operator=(std::move(rhs));
        this->obj_ = rhs.obj_;
        rhs.obj_ = nullptr;
        return *this;
    }

    T *operator->()
    {
        return obj_;
    }

    const T *operator->() const
    {
        return obj_;
    }

    T &operator*()
    {
        return *obj_;
    }

    const T &operator*() const
    {
        return *obj_;
    }

private:
    LIBCAMERA_DISABLE_COPY(SharedMemObject)

    T *obj_;
};

} /* namespace libcamera */