c++ - 无法在共享内存中使用运行时大小参数构造运行时 boost spsc_queue

Question

我想使用运行时指定的最大条目数在共享内存中创建一个无锁环形缓冲区。我的代码基于我在 GitHub 中找到的示例.我使用这段代码在共享内存中成功创建了一个无锁环形缓冲区。
在我的例子中，我需要指定环形缓冲区在运行时构造时可以接受的最大条目数，而不是每个示例的编译时。构建 shm::ring_buffer 的调用在示例中如下所示。

namespace bip = boost::interprocess;

namespace shm
{
    using char_alloc = bip::allocator<char, bip::managed_shared_memory::segment_manager>;
    using shared_string = bip::basic_string<char, std::char_traits<char>, char_alloc>;
    using ring_buffer = boost::lockfree::spsc_queue<shared_string, boost::lockfree::capacity<200>>;
}

共享内存段分配如下:

mQueuingSharedMem = std::make_unique<bip::managed_shared_memory>(
    bip::open_or_create, (mSharedMemoryName + "Queuing").c_str(), rSHMSize);

根据 GitHub 示例，当我通过可选的 boost::lockfree::capacity<> 构造具有在编译时指定的最大大小的环形缓冲区时模板参数，一切正常(注意:共享内存段 construct 方法采用 [] 中的#ring_buffers，构造函数参数在后面的括号中指定。

auto pSharedMemAddr = mQueuingSharedMem->construct<
   shm::ring_buffer>(rQueuingPortName.c_str())[1](/*aMaxNumMessages*/);

我认为为了在运行时构造上面的 shm::ring_buffer，我需要删除第二个 boost::lockfree::capacity<200>来自 shm::spsc_queue 的硬编码大小参数而是传递 shm::ring_buffer 的最大尺寸和 shm::shm_string 的共享内存分配器.我找到了类似的答案 here但我无法使其适应我的代码。

我对上面运行的代码进行了以下更改，试图在运行时指定环形缓冲区的大小:

namespace bip = boost::interprocess;
namespace shm
{
    using char_alloc = bip::allocator<char, bip::managed_shared_memory::segment_manager>;
    using shared_string = bip::basic_string<char, std::char_traits<char>, char_alloc>;
    using ring_buffer = boost::lockfree::spsc_queue<shared_string/*, boost::lockfree::capacity<200>*/>;
}

    shm::char_alloc char_alloc(mQueuingSharedMem->get_segment_manager());
    auto pSharedMemAddr = mQueuingSharedMem->construct<
        shm::ring_buffer>(rQueuingPortName.c_str())[1](aMaxNumMessages);

我收到大量无法理解的编译器错误，我不太清楚如何修复:

1>------ Build started: Project: apex, Configuration: Debug x64 ------
1>APEXManager.cpp
1>C:\Users\johnc\main\extlibs\boost_1_65_1\boost/container/string.hpp(216): error C2512: 'boost::interprocess::allocator<char,boost::interprocess::segment_manager<CharType,MemoryAlgorithm,IndexType>>::allocator': no appropriate default constructor available
1>        with
1>        [
1>            CharType=char,
1>            MemoryAlgorithm=boost::interprocess::rbtree_best_fit<boost::interprocess::mutex_family,boost::interprocess::offset_ptr<void,ptrdiff_t,uintptr_t,0>,0>,
1>            IndexType=boost::interprocess::iset_index
1>        ]
1>C:\Users\johnc\main\extlibs\boost_1_65_1\boost/container/string.hpp(214): note: while compiling class template member function 'boost::container::container_detail::basic_string_base<Allocator>::members_holder::members_holder(void)'
1>        with
1>        [
1>            Allocator=shm::char_alloc
1>        ]
1>C:\Users\johnc\main\extlibs\boost_1_65_1\boost/container/string.hpp(100): note: see reference to function template instantiation 'boost::container::container_detail::basic_string_base<Allocator>::members_holder::members_holder(void)' being compiled
1>        with
1>        [
1>            Allocator=shm::char_alloc
1>        ]
1>C:\Users\johnc\main\extlibs\boost_1_65_1\boost/container/string.hpp(224): note: see reference to class template instantiation 'boost::container::container_detail::basic_string_base<Allocator>::members_holder' being compiled
1>        with
1>        [
1>            Allocator=shm::char_alloc
1>        ]
1>C:\Users\johnc\main\extlibs\boost_1_65_1\boost/container/string.hpp(506): note: see reference to class template instantiation 'boost::container::container_detail::basic_string_base<Allocator>' being compiled
1>        with
1>        [
1>            Allocator=shm::char_alloc
1>        ]
1>C:\Users\johnc\main\extlibs\boost_1_65_1\boost/lockfree/spsc_queue.hpp(557): note: see reference to class template instantiation 'boost::container::basic_string<char,std::char_traits<char>,shm::char_alloc>' being compiled
1>C:\Users\johnc\main\extlibs\boost_1_65_1\boost/lockfree/spsc_queue.hpp(555): note: while compiling class template member function 'boost::lockfree::detail::runtime_sized_ringbuffer<T,std::allocator<T>>::~runtime_sized_ringbuffer(void)'
1>        with
1>        [
1>            T=shm::shared_string
1>        ]
1>..\..\src\apex\APEXManager.cpp(660): note: see reference to function template instantiation 'boost::lockfree::detail::runtime_sized_ringbuffer<T,std::allocator<T>>::~runtime_sized_ringbuffer(void)' being compiled
1>        with
1>        [
1>            T=shm::shared_string
1>        ]
1>C:\Users\johnc\main\extlibs\boost_1_65_1\boost/lockfree/spsc_queue.hpp(693): note: see reference to class template instantiation 'boost::lockfree::detail::runtime_sized_ringbuffer<T,std::allocator<T>>' being compiled
1>        with
1>        [
1>            T=shm::shared_string
1>        ]
1>C:\Users\johnc\main\extlibs\boost_1_65_1\boost/interprocess/detail/in_place_interface.hpp(61): note: see reference to class template instantiation 'boost::lockfree::spsc_queue<shm::shared_string>' being compiled
1>C:\Users\johnc\main\extlibs\boost_1_65_1\boost/interprocess/detail/in_place_interface.hpp(58): note: while compiling class template member function 'void boost::interprocess::ipcdetail::placement_destroy<T>::destroy_n(void *,::size_t,size_t &)'
1>        with
1>        [
1>            T=shm::ring_buffer
1>        ]
1>C:\Users\johnc\main\extlibs\boost_1_65_1\boost/interprocess/detail/named_proxy.hpp(50): note: see reference to class template instantiation 'boost::interprocess::ipcdetail::placement_destroy<T>' being compiled
1>        with
1>        [
1>            T=shm::ring_buffer
1>        ]
1>C:\Users\johnc\main\extlibs\boost_1_65_1\boost/interprocess/detail/named_proxy.hpp(130): note: see reference to class template instantiation 'boost::interprocess::ipcdetail::CtorArgN<T,false,const MESSAGE_RANGE_TYPE &>' being compiled
1>        with
1>        [
1>            T=shm::ring_buffer
1>        ]
1>..\..\src\apex\APEXManager.cpp(365): note: see reference to function template instantiation 'T *boost::interprocess::ipcdetail::named_proxy<boost::interprocess::segment_manager<CharType,MemoryAlgorithm,IndexType>,T,false>::operator ()<const MESSAGE_RANGE_TYPE&>(const MESSAGE_RANGE_TYPE &) const' being compiled
1>        with
1>        [
1>            T=shm::ring_buffer,
1>            CharType=char,
1>            MemoryAlgorithm=boost::interprocess::rbtree_best_fit<boost::interprocess::mutex_family,boost::interprocess::offset_ptr<void,ptrdiff_t,uintptr_t,0>,0>,
1>            IndexType=boost::interprocess::iset_index
1>        ]
1>..\..\src\apex\APEXManager.cpp(365): note: see reference to function template instantiation 'T *boost::interprocess::ipcdetail::named_proxy<boost::interprocess::segment_manager<CharType,MemoryAlgorithm,IndexType>,T,false>::operator ()<const MESSAGE_RANGE_TYPE&>(const MESSAGE_RANGE_TYPE &) const' being compiled
1>        with
1>        [
1>            T=shm::ring_buffer,
1>            CharType=char,
1>            MemoryAlgorithm=boost::interprocess::rbtree_best_fit<boost::interprocess::mutex_family,boost::interprocess::offset_ptr<void,ptrdiff_t,uintptr_t,0>,0>,
1>            IndexType=boost::interprocess::iset_index
1>        ]
1>Done building project "apex.vcxproj" -- FAILED.
========== Build: 0 succeeded, 1 failed, 2 up-to-date, 0 skipped ==========

Answer 1

动态大小仅在您指定进程间内存分配器时才有效:http://www.boost.org/doc/libs/1_65_1/doc/html/boost/lockfree/allocator.html .

可悲的是spsc_queue does support状态分配器:

Defines the allocator. boost.lockfree supports stateful allocator and is compatible with Boost.Interprocess allocators

它似乎不支持 uses_allocator<>将分配器向下传递到其元素 ( shared_string ) 所需的协议(protocol)，即使使用 scoped_allocator_adaptor 也不需要¹.

我之前遇到过这个:

• spsc_queue over shared_memory

• Shared-memory IPC synchronization (lock-free) (使用编译时大小 spsc_queue )

所以我的建议是去除其中一种成分:

• 使元素成为非动态容器(容器的容器总是需要作用域分配器意识或显式元素构造(
• 使队列固定大小(这对于共享内存情况通常是个好主意，IYAM)
• 添加一个间接层...

对于后者，您可以使队列存储成为受管理的 bip::shared_ptr<shared_string>相反:

Live On Coliru

#include <boost/interprocess/allocators/allocator.hpp>
#include <boost/interprocess/containers/string.hpp>
#include <boost/interprocess/managed_shared_memory.hpp>
#include <boost/interprocess/managed_mapped_file.hpp> // for Coliru
#include <boost/interprocess/smart_ptr/shared_ptr.hpp>

#include <boost/lockfree/spsc_queue.hpp>

#include <iostream>

/// noisy - traces special members
struct noisy {
    noisy& operator=(noisy&&) noexcept { std::cout << "operator=(noisy&&)\n"; return *this;      } 
    noisy& operator=(const noisy&)     { std::cout << "operator=(const noisy&)\n"; return *this; } 
    noisy(const noisy&)                { std::cout << "noisy(const noisy&)\n";                   } 
    noisy(noisy&&) noexcept            { std::cout << "noisy(noisy&&)\n";                        } 
    ~noisy()                           { std::cout << "~noisy()\n";                              } 
    noisy()                            { std::cout << "noisy()\n";                               } 
};

namespace bip = boost::interprocess;
namespace blf = boost::lockfree;

namespace Shared {
    using Segment = bip::managed_mapped_file; // Coliru unsupported: managed_shared_memory;
    using Manager = Segment::segment_manager;
    template <typename T> using Alloc = bip::allocator<T, Manager>;

    using String = bip::basic_string<char, std::char_traits<char>, Alloc<char> >;

    // using Element = String;
    // For debug/demonstration
    struct Element : String, noisy { using String::String; }; // inherit constructors

    using Ptr = bip::managed_shared_ptr<Element, Segment>::type;

    using Buffer = blf::spsc_queue<Ptr, blf::allocator<Alloc<Ptr> > >;
}

static std::string unique_id_gen() {
    static std::atomic_size_t s_gen { 0 };
    return "buffer_element" + std::to_string(++s_gen);
}

int main() {
    struct shm_remove {
        shm_remove() { bip::shared_memory_object::remove("MySharedMemory"); }
        ~shm_remove() { bip::shared_memory_object::remove("MySharedMemory"); }
    } remover;

    Shared::Segment segment(bip::create_only, "MySharedMemory", 4 << 20);

    auto& buffer = *segment.construct<Shared::Buffer>(bip::unique_instance)[1](20, segment.get_segment_manager());

    auto create = [&segment](auto&&... args) {
        return make_managed_shared_ptr(segment.construct<Shared::Element>(unique_id_gen().c_str())
                (
                    std::forward<decltype(args)>(args)...,
                    segment.get_segment_manager()
                ), segment);
    };

    std::cout << "Pushing\n";

    for (auto msg : { "hello", "world", "bye", "cruel", "world" })
        buffer.push(create(msg));

    std::cout << "Popping\n";
    {
        Shared::Ptr into;
        while (buffer.pop(into)) {
            std::cout << "Popped: '" << *into << "'\n";
        }
        std::cout << "Going out of scope\n";
    } // RAII
    std::cout << "Out of scope\n";

    {
        // make sure any other owned queue elements are freed if the queue is destroyed before it's empty:
        for (auto msg : { "HELLO", "WORLD", "BYE", "CRUEL", "WORLD" })
            buffer.push(create(msg));

        std::cout << "Destroying buffer containing 5 elements\n";
        segment.destroy<Shared::Buffer>(bip::unique_instance);
    }
}

打印:

Pushing
noisy()
noisy()
noisy()
noisy()
noisy()
Popping
Popped: 'hello'
~noisy()
Popped: 'world'
~noisy()
Popped: 'bye'
~noisy()
Popped: 'cruel'
~noisy()
Popped: 'world'
Going out of scope
~noisy()
Out of scope
noisy()
noisy()
noisy()
noisy()
noisy()
Destroying buffer containing 5 elements
~noisy()
~noisy()
~noisy()
~noisy()
~noisy()

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¹ 搜索我的答案，了解如何将这些容器与共享内存中的其他容器一起使用