slint/api/sixtyfps-cpp/include/sixtyfps_sharedarray.h

/* LICENSE BEGIN
    This file is part of the SixtyFPS Project -- https://sixtyfps.io
    Copyright (c) 2020 Olivier Goffart <olivier.goffart@sixtyfps.io>
    Copyright (c) 2020 Simon Hausmann <simon.hausmann@sixtyfps.io>

    SPDX-License-Identifier: GPL-3.0-only
    This file is also available under commercial licensing terms.
    Please contact info@sixtyfps.io for more information.
LICENSE END */
#pragma once
#include "sixtyfps_sharedarray_internal.h"
#include <atomic>

namespace sixtyfps {

template<typename T>
struct SharedArray
{
    SharedArray()
        : inner(const_cast<SharedArrayHeader*>(reinterpret_cast<const SharedArrayHeader*>(
            cbindgen_private::sixtyfps_shared_array_empty())))
    { }

    SharedArray(const SharedArray &other)
        : inner(other.inner)
    {
        if (inner->refcount > 0) {
            ++inner->refcount;
        }
    }
    ~SharedArray()
    {
        drop();
    }
    SharedArray &operator=(const SharedArray &other)
    {
        if (other.inner == inner) { return *this; }
        drop();
        inner = other.inner;
        if (inner->refcount > 0) {
            ++inner->refcount;
        }
        return *this;
    }
    SharedArray &operator=(SharedArray &&other)
    {
        std::swap(inner, other.inner);
        return *this;
    }

    const T *begin() const {
        return reinterpret_cast<const T *>(inner + 1);
    }

    const T *end() const {
        return begin() + inner->size;
    }

private:

    void drop() {
        if (inner->refcount > 0 && (--inner->refcount) == 0) {
            auto b = begin(), e = end();
            for (auto it = b; it < e; ++it) {
                it->~T();
            }
        }
        cbindgen_private::sixtyfps_shared_array_free(
            reinterpret_cast<uint8_t *>(inner),
            sizeof(SharedArrayHeader) + inner->capacity * sizeof(T),
            alignof(SharedArrayHeader));
    }

    // Unfortunately, this cannot be generated by cbindgen because std::atomic is not understood
    struct SharedArrayHeader {
        std::atomic<std::intptr_t> refcount;
        std::size_t size;
        std::size_t capacity;
    };
    static_assert(alignof(T) <= alignof(SharedArrayHeader), "Not yet supported because we would need to add padding");
    SharedArrayHeader *inner;
};
}