mmappedfile.h

/*
  Copyright (c) 2017-2019 Sven Willner <sven.willner@gmail.com>

  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.
*/

#ifndef MMAPPED_FILE_H
#define MMAPPED_FILE_H

#include <fcntl.h>
#include <sys/mman.h>
#include <unistd.h>

#include <iomanip>
#include <string>
#include <vector>

template<typename T>
inline T* open_mmapped_file(const std::string& filename, std::size_t size, char mode, int& fd) {
    T* res = nullptr;
    switch (mode) {
        case 'r': {
            fd = open(filename.c_str(), O_RDONLY | O_CLOEXEC);  // NOLINT(cppcoreguidelines-pro-type-vararg,hicpp-vararg,hicpp-signed-bitwise)
            if (fd < 0) {
                throw std::runtime_error("could not open file " + filename);
            }
            res = static_cast<T*>(mmap(nullptr, size * sizeof(T), PROT_READ, MAP_PRIVATE | MAP_POPULATE, fd, 0));  // NOLINT(hicpp-signed-bitwise)
        } break;

        case 'w': {
            fd = open(filename.c_str(), O_RDWR | O_CREAT | O_CLOEXEC,  // NOLINT(cppcoreguidelines-pro-type-vararg,hicpp-vararg,hicpp-signed-bitwise)
                      static_cast<mode_t>(0600));
            if (fd < 0) {
                throw std::runtime_error("could not create file " + filename);
            }
            int rc = lseek(fd, size * sizeof(T) - 1, SEEK_SET);
            if (rc < 0) {
                throw std::runtime_error("lseek failed");
            }
            rc = write(fd, "", 1);
            if (rc < 0) {
                throw std::runtime_error("write failed");
            }
            res = static_cast<T*>(mmap(nullptr, size * sizeof(T), PROT_WRITE, MAP_SHARED, fd, 0));
        } break;

        default:
            throw std::runtime_error("unknown file mode");
    }

    if (res == MAP_FAILED) {  // NOLINT(cppcoreguidelines-pro-type-cstyle-cast)
        throw std::runtime_error("mmap failed");
    }
    int rc = madvise(res, size * sizeof(T), MADV_WILLNEED | MADV_SEQUENTIAL);  // NOLINT(hicpp-signed-bitwise)
    if (rc < 0) {
        delete[] res;
        throw std::runtime_error("madvice failed");
    }
    return res;
}

template<typename T>
inline void close_mmapped_file(T* p, std::size_t size, int fd) {
    munmap(p, size * sizeof(T));
    close(fd);
}

template<typename T = char>
class MMappedFile {
  protected:
    int fd = 0;
    std::unique_ptr<T[]> data;
    std::size_t size_m = 0;

  public:
    MMappedFile() = default;
    MMappedFile(const MMappedFile&) = delete;
    MMappedFile(MMappedFile&&) noexcept = default;

    void open(const std::string& filename, std::size_t size_p, char mode = '\r') {
        close();
        data.reset(open_mmapped_file<T>(filename, size_p, mode, fd));
        size_m = size_p;
    }

    void close() {
        if (data) {
            close_mmapped_file<T>(data.get(), size_m, fd);
            data.release();
            size_m = 0;
        }
    }

    ~MMappedFile() { close(); }
    constexpr operator bool() const { return data; }  // NOLINT(google-explicit-constructor,hicpp-explicit-conversions)
    constexpr T* get() { return data.get(); }
    constexpr T* get() const { return data.get(); }
    constexpr std::size_t size() const { return size_m; }
};

#endif