c++ - 抛出错误的分配

标签 c++ memory boost bad-alloc

我在尝试使用 boost 托管共享内存时收到“bad_alloc”。我已经从他们针对不耐烦的快速指南中复制了 boost 示例，并加入了我自己的更改。我的代码在下面，我已经注释掉了示例内容并在下面写了我自己的代码。我还添加了一些调试和测试内容。

有人有什么想法吗？非常感谢任何帮助!

-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;

}

这是我的程序输出...

 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

最佳答案

看来您只是内存不足。您可能会认为您不应该这样做，因为各个分配不占用空间量。

但是内存碎片可以做到这一点:如果共享内存对象有足够的“填充”或“开销”，您可能会耗尽可连续分配的空间。

要么将您的数据存储在预先分配的 vector 中(例如)，要么使用一种更智能的进程间分配算法:

在这种情况下解决它的最简单方法似乎只是将共享内存区域扩大两倍(无论如何，在大多数系统上最小大小是 4K 内存页面)。

我刚刚使用了 2*size 并且测试运行完成。

更新/修复

我刚刚证实，确实以“vector 方式”做事效率更高:用 boost 的 flat_map 替换 std::map 可以获得 vector 存储。

最大的区别是 map 中的每个节点都是动态分配的，产生固定的开销，线性消耗可用内存。

enter image description here

观察

  • 有相当大的初始开销，在发生任何事情之前消耗了 320 个字节。
  • 使用flat_map，您还预先保留了 vector 容量，您会发现您可以获得一点额外的存储效率。

上图是根据以下程序的输出创建的。查找对 get_free_memory() 的调用。要切换 map 实现，只需将 #if 0 更改为 #if 1。 (请注意我是如何清理一些不必要的重复代码并使用异常进行流量控制的)。

#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";
    }
}

关于c++ - 抛出错误的分配，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/21287171/

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