c++ - 不正な割り当てがスローされます

Question

ブースト マネージド共有メモリを使用しようとしているときに、「bad_alloc」が発生します。せっかちな人向けのクイック ガイドからブーストの例をコピーし、独自の変更を組み込みました。私のコードは以下のとおりです。例をコメントアウトし、その下に自分のコードを書きました。また、デバッグとテスト用のものもいくつか入れました。

誰にもアイデアはありますか？どんな助けでも大歓迎です！

-M

#include <boost/interprocess/managed_shared_memory.hpp>
#include <boost/interprocess/containers/map.hpp>
#include <boost/interprocess/allocators/allocator.hpp>
#include <boost/interprocess/containers/string.hpp>
#include <boost/interprocess/exceptions.hpp>

#include <functional>
#include <utility>
#include <iostream>
#include <string>

#define space_name "MySharedMemorydfgdfhgd"
namespace std{


}

int main ()
{

using namespace boost::interprocess;


//Remove shared memory on construction and destruction

struct shm_remove
{
    shm_remove() { shared_memory_object::remove(space_name); }
    ~shm_remove(){ shared_memory_object::remove(space_name); }
} remover;

typedef int    KeyType;
typedef boost::interprocess::managed_shared_memory::allocator<char>::type char_allocator;
//typedef boost::interprocess::allocator<char, boost::interprocess::managed_shared_memory::segment_manager> char_allocator;
typedef boost::interprocess::basic_string<char, std::char_traits<char>, char_allocator> shm_string;

struct certificateStorage{
    int certificate_id;        
    certificateStorage( int _certificate_id, const char* _certificate, const char* _key, const char_allocator &al) :
    certificate_id(_certificate_id) 
    {}
};

//Note that map<Key, MappedType>'s value_type is std::pair<const Key, MappedType>,
//so the allocator must allocate that pair.

//typedef std::pair<const int, float> ValueType;
typedef std::pair<const int, certificateStorage> certValueType;
//typedef allocator<ValueType, managed_shared_memory::segment_manager> ShmemAllocator;
typedef allocator<certValueType, boost::interprocess::managed_shared_memory::segment_manager> certShmemAllocator;
//typedef map<KeyType, MappedType, std::less<KeyType>, ShmemAllocator> MyMap;
typedef map<KeyType, certificateStorage, std::less<KeyType>, certShmemAllocator> certSHMMap;
// typedef boost::interprocess::map<KeyType, int, std::less<KeyType>, certShmemAllocator> certSHMMap;

std::cout << "\n\n\nStarting the program.\n\n\n";

//Shared memory front-end that is able to construct objects
//associated with a c-string. Erase previous shared memory with the name
//to be used and create the memory segment at the specified address and initialize resources

const int numentries = 20;
const char* elementName = "mymap";
int size = sizeof(certificateStorage) * numentries + 1000;
std::cout << "SHM size is " <<size<< " bytes \n";
int runningsize = 0;


try{
    //this stayed the same
    managed_shared_memory shm_segment
    (create_only
    ,space_name//segment name
    ,size);   

    certSHMMap *mymap;

    //Initialize the shared memory STL-compatible allocator
    //ShmemAllocator alloc_inst (segment.get_segment_manager());
    certShmemAllocator alloc_inst (shm_segment.get_segment_manager());
    char_allocator ca(shm_segment.get_allocator<char>());

    for(int i = 0; i < numentries; i++){

        try{
            //MyMap *mymap =
            // segment.construct<MyMap>("MyMap")      //object name
            //(std::less<int>() //first  ctor parameter
            //  ,alloc_inst);     //second ctor parameter              

            mymap = shm_segment.construct<certSHMMap>(elementName)
            (std::less<int>() 
            ,alloc_inst);     //object name
        }
        catch(boost::interprocess::interprocess_exception &ex){
            std::cout << "Certificates element already exists.";

            try{
                mymap = shm_segment.find<certSHMMap>(elementName).first;   //object name
                 std::cout << " Fetching existing pointer.\n";
            }
            catch(boost::interprocess::interprocess_exception &ex){
                std::cout << "\nCertificates object wont load\n";
                mymap = shm_segment.find<certSHMMap>(elementName).first;   //object name
            }
        }

        certificateStorage thisCert(i, "", "", ca);
         std::cout << "Created object.\n";
        mymap->insert(certValueType(i, thisCert));
         std::cout << "Inserted object. " << i <<" size is " <<sizeof(thisCert)  << " \n";
         runningsize += sizeof(thisCert) ;
         std::cout << "SHM Current size is " << runningsize << " / " << size << "\n";
    }

    std::cout << "\n\nDone Inserting\nStarting output\n.";
    /*    
        //Insert data in the map
        for(int i = 0; i < 100; ++i){
        mymap->insert(std::pair<const int, float>(i, (float)(i*i)));
        }

        for(int i = 0; i < 100; ++i){
        std::cout << "Key: " << i << " Value: " << mymap->at(i) << "\n";

        mymap->insert(std::pair<const int, float>(i, (float)(i*2)));
    } */


    for(int i = 0; i < numentries; i++){

        try{
            mymap = shm_segment.construct<certSHMMap>(elementName)(std::less<int>() ,alloc_inst);     //object name
        }
        catch(boost::interprocess::interprocess_exception &ex){
            std::cout << "Certificates element already exists.\n";

            try{
                mymap = shm_segment.find<certSHMMap>(elementName).first;   //object name
            }
            catch(boost::interprocess::interprocess_exception &ex){
                std::cout << "Certificates object wont load\n";
                mymap = shm_segment.find<certSHMMap>(elementName).first;   //object name
            }
        }
        certificateStorage tmp = mymap->at(i);
        std::cout << "The key is: " << i << " And the value is: " << tmp.certificate_id;
    }
}
catch(boost::interprocess::interprocess_exception &ex){
    std::cout << "\n shm space wont load wont load\n";
    std::cout << "\n Why: " << ex.what() << "\n";


}
shared_memory_object::remove(space_name);
return 0;

}

そして、ここに私のプログラム出力があります...

 Starting the program.


SHM size is 1080 bytes
Created object.
Inserted object. 0 size is 4
SHM Current size is 4 / 1080
Certificates element already exists. Fetching existing pointer.
Created object.
Inserted object. 1 size is 4
SHM Current size is 8 / 1080
Certificates element already exists. Fetching existing pointer.
Created object.
Inserted object. 2 size is 4
SHM Current size is 12 / 1080
Certificates element already exists. Fetching existing pointer.
Created object.
Inserted object. 3 size is 4
SHM Current size is 16 / 1080
Certificates element already exists. Fetching existing pointer.
Created object.
Inserted object. 4 size is 4
SHM Current size is 20 / 1080
Certificates element already exists. Fetching existing pointer.
Created object.
Inserted object. 5 size is 4
SHM Current size is 24 / 1080
Certificates element already exists. Fetching existing pointer.
Created object.
Inserted object. 6 size is 4
SHM Current size is 28 / 1080
Certificates element already exists. Fetching existing pointer.
Created object.
Inserted object. 7 size is 4
SHM Current size is 32 / 1080
Certificates element already exists. Fetching existing pointer.
Created object.
Inserted object. 8 size is 4
SHM Current size is 36 / 1080
Certificates element already exists. Fetching existing pointer.
Created object.
Inserted object. 9 size is 4
SHM Current size is 40 / 1080
Certificates element already exists. Fetching existing pointer.
Created object.
Inserted object. 10 size is 4
SHM Current size is 44 / 1080
Certificates element already exists. Fetching existing pointer.
Created object.
Inserted object. 11 size is 4
SHM Current size is 48 / 1080
Certificates element already exists. Fetching existing pointer.
Created object.
Inserted object. 12 size is 4
SHM Current size is 52 / 1080
Certificates element already exists. Fetching existing pointer.
Created object.
Inserted object. 13 size is 4
SHM Current size is 56 / 1080
Certificates element already exists. Fetching existing pointer.
Created object.
Inserted object. 14 size is 4
SHM Current size is 60 / 1080
Certificates element already exists. Fetching existing pointer.
Created object.
Inserted object. 15 size is 4
SHM Current size is 64 / 1080
Certificates element already exists. Fetching existing pointer.
Created object.

 shm space wont load wont load

 Why: boost::interprocess::bad_alloc

Answer 1

単にメモリが不足しているようです。個々の割り当てがスペースの量を占有しないため、そうすべきではないと考えるかもしれません。

しかし、メモリの断片化はこれを行うことができます: 共有メモリ オブジェクトに十分な「パディング」または「オーバーヘッド」がある場合、連続して割り当て可能なスペースが不足する可能性があります。

データを事前に割り当てられたベクトル (例) に格納するか、よりスマートなプロセス間割り当てアルゴリズムのいずれかを使用します。

• http://www.boost.org/doc/libs/1_55_0/doc/html/interprocess/allocators_containers.html

この場合、これを解決する最も簡単な方法は、共有メモリ領域を 2 倍にすることです (最小サイズは、ほとんどのシステムで 4K メモリ ページです)。

使用したばかり2*sizeで、テストは完了しました。

更新/修正

実際に「ベクター方式」で行う方がはるかに効率的であることを確認したところです。boost に置き換えるとstd::map、flat_mapベクター ストレージが得られます。

大きな違いは、マップ内の各ノードが動的に割り当てられるため、固定のオーバーヘッドが発生し、使用可能なメモリが直線的に消費されることです。

観察

• 何かが起こる前に 320 バイトを消費する、かなりの初期オーバーヘッドがあります。
• を使用するとflat_map、前もってベクトル容量を予約することもできます。これにより、ストレージ効率がわずかに向上することがわかります。

上記のグラフは、次のプログラムの出力から作成されました。への呼び出しを探しますget_free_memory()。map実装を切り替えるには、 に変更#if 0するだけ#if 1です。(不必要に繰り返し、フロー制御に例外を使用していたコードの一部をクリーンアップした方法に注意してください) .

#include <boost/interprocess/managed_shared_memory.hpp>
#include <boost/interprocess/containers/map.hpp>
#include <boost/interprocess/allocators/allocator.hpp>
#include <boost/interprocess/containers/string.hpp>
#include <boost/interprocess/containers/flat_map.hpp>
#include <boost/interprocess/exceptions.hpp>

#include <functional>
#include <utility>
#include <iostream>
#include <string>

#define space_name "MySharedMemory"

int main ()
{
    using namespace boost::interprocess;
    //Remove shared memory on construction and destruction

    struct shm_remove
    {
        shm_remove() { shared_memory_object::remove(space_name); }
        ~shm_remove(){ shared_memory_object::remove(space_name); }
    } remover;

    typedef int KeyType;
    typedef boost::interprocess::managed_shared_memory::allocator<char>::type char_allocator;
    //typedef boost::interprocess::allocator<char, boost::interprocess::managed_shared_memory::segment_manager> char_allocator;
    //typedef boost::interprocess::basic_string<char, std::char_traits<char>, char_allocator> shm_string;

    struct certificateStorage{
        int certificate_id;        
        certificateStorage( int _certificate_id, const char* _certificate, const char* _key, const char_allocator &al) :
            certificate_id(_certificate_id) 
        {}
    };

#if 0 // STL
    typedef std::pair<const int, certificateStorage> certValueType;
    typedef allocator<certValueType, boost::interprocess::managed_shared_memory::segment_manager> certShmemAllocator;
    typedef map<KeyType, certificateStorage, std::less<KeyType>, certShmemAllocator> certSHMMap;
#else // FLAT_MAP
    typedef std::pair<int, certificateStorage> certValueType; // not const key for flat_map
    typedef allocator<certValueType, boost::interprocess::managed_shared_memory::segment_manager> certShmemAllocator;
    typedef boost::container::flat_map<KeyType, certificateStorage, std::less<KeyType>, certShmemAllocator> certSHMMap;
#endif 

    std::cout << "\n\n\nStarting the program.\n\n\n";

    const int numentries    = 20;
    const char* elementName = "mymap";
    int size                = sizeof(certificateStorage) * numentries + 1000;
    int runningsize         = 0;

    std::cout << "SHM size is " <<size<< " bytes \n";

    try{
        managed_shared_memory shm_segment(create_only, space_name/*segment name*/, size);   

        certShmemAllocator alloc_inst (shm_segment.get_segment_manager());
        char_allocator ca(shm_segment.get_allocator<char>());

        certSHMMap *mymap = shm_segment.find_or_construct<certSHMMap>(elementName)
            (std::less<int>(), alloc_inst);

        mymap->reserve(numentries);

        for(int i = 0; i < numentries; i++){
            std::cout << "Free memory: " << shm_segment.get_free_memory() << "\n";

            certificateStorage thisCert(i, "", "", ca);
            std::cout << "Created object.\n";
            mymap->insert(certValueType(i, thisCert));
            std::cout << "Inserted object. " << i <<" size is " <<sizeof(thisCert)  << " \n";
            runningsize += sizeof(thisCert) ;
            std::cout << "SHM Current size is " << runningsize << " / " << size << "\n";
        }

        std::cout << "\n\nDone Inserting\nStarting output\n";

        for(int i = 0; i < numentries; i++){
            certificateStorage tmp = mymap->at(i);
            std::cout << "The key is: " << i << " And the value is: " << tmp.certificate_id << "\n";
        }
    }
    catch(boost::interprocess::interprocess_exception &ex){
        std::cout << "\n shm space wont load wont load\n";
        std::cout << "\n Why: " << ex.what() << "\n";
    }
}