Boost C++ 库

Boost.Unordered 容器与 Interprocess 兼容，因此程序员可以将哈希容器存储在共享内存和内存映射文件中。这是一个在共享内存中存储 unordered_map 的小例子

#include <boost/interprocess/managed_shared_memory.hpp>
#include <boost/interprocess/allocators/allocator.hpp>


#include <boost/unordered_map.hpp>     //boost::unordered_map


#include <functional>                  //std::equal_to
#include <boost/container_hash/hash.hpp>   //boost::hash


int main ()
{
   using namespace boost::interprocess;
   //Remove shared memory on construction and destruction
   struct shm_remove
   {
      shm_remove() { shared_memory_object::remove("MyName"); }
      ~shm_remove(){ shared_memory_object::remove("MyName"); }
   } remover;

   //Create shared memory
   managed_shared_memory segment(create_only, "MyName", 65536);

   //Note that unordered_map<Key, MappedType>'s value_type is std::pair<const Key, MappedType>,
   //so the allocator must allocate that pair.
   typedef int    KeyType;
   typedef float  MappedType;
   typedef std::pair<const int, float> ValueType;

   //Typedef the allocator
   typedef allocator<ValueType, managed_shared_memory::segment_manager> ShmemAllocator;

   //Alias an unordered_map of ints that uses the previous STL-like allocator.
   typedef boost::unordered_map
      < KeyType               , MappedType
      , boost::hash<KeyType>  ,std::equal_to<KeyType>
      , ShmemAllocator>
   MyHashMap;

   //Construct a shared memory hash map.
   //Note that the first parameter is the initial bucket count and
   //after that, the hash function, the equality function and the allocator
   MyHashMap *myhashmap = segment.construct<MyHashMap>("MyHashMap")  //object name
      ( 3u, boost::hash<int>(), std::equal_to<int>()                  //
      , segment.get_allocator<ValueType>());                         //allocator instance

   //Insert data in the hash map
   for(std::size_t i = 0; i < 100u; ++i){
      myhashmap->insert(ValueType((int)i, (float)i));
   }
   return 0;
}

广泛使用的 Boost.MultiIndex 库与 Boost.Interprocess 兼容，因此我们可以在共享内存中构建相当不错的数据库。在共享内存中构建数据库比在普通内存中更困难一些，通常是因为这些数据库包含字符串，而这些字符串需要放置在共享内存中。共享内存字符串在其构造函数中需要分配器，因此这通常使对象插入变得更加复杂。

这是一个展示如何将多索引容器放入共享内存的例子

#include <boost/interprocess/managed_shared_memory.hpp>
#include <boost/interprocess/allocators/allocator.hpp>
#include <boost/container/string.hpp>


#include <boost/multi_index_container.hpp>
#include <boost/multi_index/member.hpp>
#include <boost/multi_index/ordered_index.hpp>


using namespace boost::interprocess;
namespace bmi = boost::multi_index;

typedef managed_shared_memory::allocator<char>::type              char_allocator;
typedef boost::container::basic_string<char, std::char_traits<char>, char_allocator>shm_string;

//Data to insert in shared memory
struct employee
{
   int         id;
   int         age;
   shm_string  name;
   employee( int id_
           , int age_
           , const char *name_
           , const char_allocator &a)
      : id(id_), age(age_), name(name_, a)
   {}
};

//Tags
struct id{};
struct age{};
struct name{};

// Define a multi_index_container of employees with following indices:
//   - a unique index sorted by employee::int,
//   - a non-unique index sorted by employee::name,
//   - a non-unique index sorted by employee::age.
typedef bmi::multi_index_container<
  employee,
  bmi::indexed_by<
    bmi::ordered_unique
      <bmi::tag<id>,  bmi::member<employee,int,&employee::id> >,
    bmi::ordered_non_unique<
      bmi::tag<name>, bmi::member<employee,shm_string,&employee::name> >,
    bmi::ordered_non_unique
      <bmi::tag<age>, bmi::member<employee,int,&employee::age> > >,
  managed_shared_memory::allocator<employee>::type
> employee_set;

int main ()
{
   //Remove shared memory on construction and destruction
   struct shm_remove
   {
      shm_remove() { shared_memory_object::remove("MyName"); }
      ~shm_remove(){ shared_memory_object::remove("MyName"); }
   } remover;

   //Create shared memory
   managed_shared_memory segment(create_only,"MyName", 65536);

   //Construct the multi_index in shared memory
   employee_set *es = segment.construct<employee_set>
      ("My MultiIndex Container")            //Container's name in shared memory
      ( employee_set::ctor_args_list()
      , segment.get_allocator<employee>());  //Ctor parameters

   //Now insert elements
   char_allocator ca(segment.get_allocator<char>());
   es->insert(employee(0,31, "Joe", ca));
   es->insert(employee(1,27, "Robert", ca));
   es->insert(employee(2,40, "John", ca));
   return 0;
}