如何将文件放入 boost::interprocess::managed_shared_memory 中?

本文介绍了如何将文件放入 boost::interprocess::managed_shared_memory 中?的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！

问题描述

如何将任意名称和任意大小的文件放入boost::interprocess::managed_shared_memory?

注意，我的意思不是 boost::interprocess::managed_mapped_file 或boost::interprocess::file_mapping.

我选择了 managed_shared_memory 因为其他选项需要固定的文件名要指定，但我需要传输不同名称的文件.

我需要使用 boost，而不是 Win32 API.

我翻遍了互联网上的大量信息，但没有找到合适的.

因此，我向您寻求帮助.我将不胜感激.

解决方案

共享内存管理段包含任意对象.所以你定义了一个像

这样的对象

 struct MyFile {std::string _filename;std::vector_内容;};

并将其存储在那里.但是，等等，不要那么快，因为这些只能用进程间分配器安全地存储，所以添加一些魔法酱(也就是很多有趣的 typedef 来声明分配器，以及一些构造函数):>

命名空间共享{使用 Mem = bip::managed_shared_memory;使用 Mgr = Mem::segment_manager;模板 使用 Alloc = bc::scoped_allocator_adaptor>;模板 使用 Vector = bc::vector;使用字符串 =bc::basic_string<char, std::char_traits<char>, Alloc<char>>;结构我的文件{使用 allocator_type = Alloc;模板 显式 MyFile(std::string_view name, It b, It e, allocator_type alloc)字符串_文件名；向量_内容;};}

现在您可以将文件存储为:

Shared::Mem shm(bip::open_or_create, shared_mem", 10ull <(file1")(file.native(), data_begin, data_end,shm.get_segment_manager());

请注意，共享内存实际上不会立即占用 30GiB，即使这就是 10ull <<30 指定.在大多数操作系统上，这将是零散分配，只提交包含数据的页面.

改进

您可能想知道 scoped_allocator_adaptor 是干什么用的.我们好像没有用过?

嗯，我们的想法是不直接为每个文件使用 find_or_construct，而是存储一个 Vector，以便您可以利用 BIP 分配器的全部功能.

可以调用以下完整演示

带有文件名参数，它们都将被加载(如果它们作为常规文件)
不带参数，将列出之前加载的文件

请注意，此方法中存在文件大小限制，因为消息具有最大长度

`TCP 套接字版本`

这是一个 TCP 套接字实现.

注意这如何轻松扩展到更大的文件、单个连接中的多个文件，甚至如果需要，甚至可以同时扩展多个连接.它也不做双缓冲，从而提高了性能.这就是为什么这种方法比您的任何其他方法更常见.

How to put a file with an arbitrary name and arbitrary size into a boost::interprocess::managed_shared_memory?

Note, I donot mean boost::interprocess::managed_mapped_file orboost::interprocess::file_mapping.

I chose managed_shared_memory because other options require a fixed file nameto be specified but I need to transfer files with different names.

I need to use boost, not Win32 API.

I rummaged through a huge amount of information on the Internet, but did notfind anything suitable.

Therefore, I am asking you for help. I would be very grateful to you.

解决方案

Shared memory managed segments contain arbitrary objects. So you define an object like

 struct MyFile {
     std::string _filename;
     std::vector<char> _contents;
 };

And store it there. But, wait, not so quick, because these can only be stored safely with interprocess allocators, so adding some magic sauce (a.k.a lots of interesting typedefs to get the allocators declared, and some constructors):

namespace Shared {
    using Mem = bip::managed_shared_memory;
    using Mgr = Mem::segment_manager;

    template <typename T>
    using Alloc = bc::scoped_allocator_adaptor<bip::allocator<T, Mgr>>;

    template <typename T> using Vector = bc::vector<T, Alloc<T>>;
    using String =
        bc::basic_string<char, std::char_traits<char>, Alloc<char>>;

    struct MyFile {
        using allocator_type = Alloc<char>;

        template <typename It>
        explicit MyFile(std::string_view name, It b, It e, allocator_type alloc)

        String _filename;
        Vector<char> _contents;
    };
}

Now you can store your files like:

Shared::Mem shm(bip::open_or_create, "shared_mem", 10ull << 30);

std::ifstream ifs("file_name.txt", std::ios::binary);
std::istreambuf_iterator<char> data_begin{ifs}, data_end{};

auto loaded = shm.find_or_construct<Shared::MyFile>("file1")(
        file.native(), data_begin, data_end,
         shm.get_segment_manager());

`Improving`

You might have wondered what the scoped_allocator_adaptor was for. It doesn't seem we use it?

Well, the idea was to not use find_or_construct directly per file, but tostore a Vector<MyFile so you can harness the full power of BIP allocators.

The following full demo can be invoked

with filename arguments, which will all be loaded (if they exist asregular files)
without arguments, which will list previously loaded files

Live On Coliru

#include <boost/interprocess/managed_shared_memory.hpp>
#include <boost/interprocess/managed_mapped_file.hpp> // for COLIRU
#include <boost/interprocess/containers/vector.hpp>
#include <boost/interprocess/containers/string.hpp>
#include <boost/container/scoped_allocator.hpp>
#include <fstream>
#include <filesystem>
#include <iostream>
#include <iomanip>

namespace bip = boost::interprocess;
namespace bc = boost::container;
namespace fs = std::filesystem;

namespace Shared {
#ifdef COLIRU
    using Mem = bip::managed_mapped_file; // managed_shared_memory not allows
#else
    using Mem = bip::managed_shared_memory;
#endif
    using Mgr = Mem::segment_manager;

    template <typename T>
    using Alloc = bc::scoped_allocator_adaptor<bip::allocator<T, Mgr>>;

    template <typename T> using Vector = bc::vector<T, Alloc<T>>;
    using String = bc::basic_string<char, std::char_traits<char>, Alloc<char>>;

    struct MyFile {
        using allocator_type = Alloc<char>;

        MyFile(MyFile&&) = default;
        MyFile(MyFile const& rhs, allocator_type alloc)
            : _filename(rhs._filename.begin(), rhs._filename.end(), alloc),
              _contents(rhs._contents.begin(), rhs._contents.end(), alloc) {}

        MyFile& operator=(MyFile const& rhs) {
            _filename.assign(rhs._filename.begin(), rhs._filename.end());
            _contents.assign(rhs._contents.begin(), rhs._contents.end());
            return *this;
        }

        template <typename It>
        explicit MyFile(std::string_view name, It b, It e, allocator_type alloc)
            : _filename(name.data(), name.size(), alloc),
              _contents(b, e, alloc) {}

        String _filename;
        Vector<char> _contents;

        friend std::ostream& operator<<(std::ostream& os, MyFile const& mf) {
            return os << "Name: " << std::quoted(mf._filename.c_str())
                      << " content size: " << mf._contents.size();
        }
    };
} // namespace Shared

int main(int argc, char** argv) {
    Shared::Mem shm(bip::open_or_create, "shared_mem", 512ull << 10);

    using FileList = Shared::Vector<Shared::MyFile>;
    auto& shared_files =
        *shm.find_or_construct<FileList>("FileList")(shm.get_segment_manager());

    if (1==argc) {
        std::cout << "Displaying previously loaded files: \n";
        for (auto& entry : shared_files)
            std::cout << entry << std::endl;
    } else {
        std::cout << "Loading files: \n";
        for (auto file : std::vector<fs::path>{argv + 1, argv + argc}) {
            if (is_regular_file(file)) {
                try {
                    std::ifstream ifs(file, std::ios::binary);
                    std::istreambuf_iterator<char> data_begin{ifs}, data_end{};

                    auto& loaded = shared_files.emplace_back(
                        file.native(), data_begin, data_end);

                    std::cout << loaded << std::endl;
                } catch (std::system_error const& se) {
                    std::cerr << "Error: " << se.code().message() << std::endl;
                } catch (std::exception const& se) {
                    std::cerr << "Other: " << se.what() << std::endl;
                }
            }
        }
    }
}

When run with

g++ -std=c++17 -O2 -Wall -pedantic -pthread main.cpp -lrt -DCOLIRU
./a.out main.cpp a.out
./a.out

Prints

Loading files:
Name: "main.cpp" content size: 3239
Name: "a.out" content size: 175176
Displaying previously loaded files:
Name: "main.cpp" content size: 3239
Name: "a.out" content size: 175176

`BONUS`

In response to the comments, I think it's worth actually comparing

`Message Queue version`

For comparison, here's a message queue implementation

Live On Coliru

#include <boost/interprocess/ipc/message_queue.hpp>
#include <boost/endian/arithmetic.hpp>
#include <fstream>
#include <filesystem>
#include <iostream>
#include <iomanip>

namespace bip = boost::interprocess;
namespace fs = std::filesystem;
using bip::message_queue;
static constexpr auto MAX_FILENAME_LENGH = 512; // 512 bytes max filename length
static constexpr auto MAX_CONTENT_SIZE = 512ull << 10; // 512 KiB max payload size

struct Message {
    std::vector<char> _buffer;

    using Uint32 = boost::endian::big_uint32_t;
    struct header_t {
        Uint32 filename_length;
        Uint32 content_size;
    };
    static_assert(std::is_standard_layout_v<header_t> and
                  std::is_trivial_v<header_t>);

    Message() = default;

    Message(fs::path file) {
        std::string const name = file.native();
        std::ifstream ifs(file, std::ios::binary);
        std::istreambuf_iterator<char> data_begin{ifs}, data_end{};

        _buffer.resize(header_len + name.length());
        std::copy(begin(name), end(name), _buffer.data() + header_len);
        _buffer.insert(_buffer.end(), data_begin, data_end);
        header().filename_length = name.length();
        header().content_size    = size() - header_len - name.length();
    }

    Message(char const* buf, size_t size)
        : _buffer(buf, buf+size) {}

    static constexpr auto header_len = sizeof(header_t);
    static constexpr auto max_size =
        header_len + MAX_FILENAME_LENGH + MAX_CONTENT_SIZE;

    char const* data() const { return _buffer.data(); }
    size_t size() const      { return _buffer.size(); }

    header_t& header() {
        assert(_buffer.size() >= header_len);
        return *reinterpret_cast<header_t*>(_buffer.data());
    }

    header_t const& header() const {
        assert(_buffer.size() >= header_len);
        return *reinterpret_cast<header_t const*>(_buffer.data());
    }

    std::string_view filename() const {
        assert(_buffer.size() >= header_len + header().filename_length);
        return { _buffer.data() + header_len, header().filename_length };
    }

    std::string_view contents() const {
        assert(_buffer.size() >=
                header_len + header().filename_length + header().content_size);

        return {_buffer.data() + header_len + header().filename_length,
            header().content_size};
    }

    friend std::ostream& operator<<(std::ostream& os, Message const& mf) {
        return os << "Name: " << std::quoted(mf.filename())
                  << " content size: " << mf.contents().size();
    }
};

int main(int argc, char** argv) {
    message_queue mq(bip::open_or_create, "file_transport", 10, Message::max_size);

    if (1==argc) {
        std::cout << "Receiving uploaded files: \n";
        char rawbuf [Message::max_size];
        while (true) {
            size_t n;
            unsigned prio;
            mq.receive(rawbuf, sizeof(rawbuf), n, prio);

            Message decoded(rawbuf, n);
            std::cout << "Received: " << decoded << std::endl;
        }
    } else {
        std::cout << "Loading files: \n";
        for (auto file : std::vector<fs::path>{argv + 1, argv + argc}) {
            if (is_regular_file(file)) {
                try {
                    Message encoded(file);
                    std::cout << "Sending: " << encoded << std::endl;

                    mq.send(encoded.data(), encoded.size(), 0);
                } catch (std::system_error const& se) {
                    std::cerr << "Error: " << se.code().message() << std::endl;
                } catch (std::exception const& se) {
                    std::cerr << "Other: " << se.what() << std::endl;
                }
            }
        }
    }
}

A demo:

`TCP Socket Version`

Here's a TCP socket implementation.

Live On Coliru

#include <boost/asio.hpp>
#include <boost/endian/arithmetic.hpp>
#include <vector>
#include <fstream>
#include <filesystem>
#include <iostream>
#include <iomanip>

namespace fs = std::filesystem;
using boost::asio::ip::tcp;
using boost::system::error_code;
static constexpr auto MAX_FILENAME_LENGH = 512; // 512 bytes max filename length
static constexpr auto MAX_CONTENT_SIZE = 512ull << 10; // 512 KiB max payload size

struct Message {
    std::vector<char> _buffer;

    using Uint32 = boost::endian::big_uint32_t;
    struct header_t {
        Uint32 filename_length;
        Uint32 content_size;
    };
    static_assert(std::is_standard_layout_v<header_t> and
                  std::is_trivial_v<header_t>);

    Message() = default;

    Message(fs::path file) {
        std::string const name = file.native();
        std::ifstream ifs(file, std::ios::binary);
        std::istreambuf_iterator<char> data_begin{ifs}, data_end{};

        _buffer.resize(header_len + name.length());
        std::copy(begin(name), end(name), _buffer.data() + header_len);
        _buffer.insert(_buffer.end(), data_begin, data_end);
        header().filename_length = name.length();
        header().content_size    = actual_size() - header_len - name.length();
    }

    Message(char const* buf, size_t size)
        : _buffer(buf, buf+size) {}

    static constexpr auto header_len = sizeof(header_t);
    static constexpr auto max_size =
        header_len + MAX_FILENAME_LENGH + MAX_CONTENT_SIZE;

    char const* data() const { return _buffer.data(); }
    size_t actual_size() const { return _buffer.size(); }
    size_t decoded_size() const {
        return header().filename_length + header().content_size;
    }
    bool is_complete() const {
        return actual_size() >= header_len && actual_size() >= decoded_size();
    }

    header_t& header() {
        assert(actual_size() >= header_len);
        return *reinterpret_cast<header_t*>(_buffer.data());
    }

    header_t const& header() const {
        assert(actual_size() >= header_len);
        return *reinterpret_cast<header_t const*>(_buffer.data());
    }

    std::string_view filename() const {
        assert(actual_size() >= header_len + header().filename_length);
        return std::string_view(_buffer.data() + header_len,
                                header().filename_length);
    }

    std::string_view contents() const {
        assert(actual_size() >= decoded_size());

        return std::string_view(_buffer.data() + header_len +
                                    header().filename_length,
                                header().content_size);
    }

    friend std::ostream& operator<<(std::ostream& os, Message const& mf) {
        return os << "Name: " << std::quoted(mf.filename())
                  << " content size: " << mf.contents().size();
    }
};

int main(int argc, char** argv) {
    boost::asio::io_context ctx;
    u_int16_t port = 8989;

    if (1==argc) {
        std::cout << "Receiving uploaded files: " << std::endl;
        tcp::acceptor acc(ctx, tcp::endpoint{{}, port});

        while (true) {
            auto s = acc.accept();
            std::cout << "Connection accepted from " << s.remote_endpoint() << std::endl;

            Message msg;
            auto buf = boost::asio::dynamic_buffer(msg._buffer);
            error_code ec;
            while (auto n = read(s, buf, ec)) {
                std::cout << "(read " << n << " bytes, " << ec.message() << ")" << std::endl;

                while (msg.is_complete()) {
                    std::cout << "Received: " << msg << std::endl;
                    buf.consume(msg.decoded_size() + Message::header_len);
                }
            }
            std::cout << "Connection closed" << std::endl;
        }
    } else {
        std::cout << "Loading files: " << std::endl;
        tcp::socket s(ctx);
        s.connect(tcp::endpoint{{}, port});

        for (auto file : std::vector<fs::path>{argv + 1, argv + argc}) {
            if (is_regular_file(file)) {
                try {
                    Message encoded(file);
                    std::cout << "Sending: " << encoded << std::endl;

                    write(s, boost::asio::buffer(encoded._buffer));
               } catch (std::system_error const& se) {
                    std::cerr << "Error: " << se.code().message() << std::endl;
                } catch (std::exception const& se) {
                    std::cerr << "Other: " << se.what() << std::endl;
                }
            }
        }
    }
}

Demo:

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