c++中使用boost库在共享内存中存储map

boost库中的interprocess包可以在共享内存中创建map等复杂类型的数据，
但是不能用std::map，主要原因时其中的指针用的绝对位置，而非相对的
用boost的map，vector等类型，必须显示的指定allocator，因而复杂了不少。

代码小而全的一个实现：http://blog.csdn.net/dx2880/article/details/7315761


我在学习的过程中参考了错误的代码，走了不少弯路。这里贴出的示例主要是将
创建共享内存  和 使用共享内存中的数据  两部分分离成为了两个程序，更符合一般的使用场景（但其实类定义应该引用一个文件）：

注意：经测试，在创建共享内存的程序中修改Item类定义，比如在最后新加一个int tmp; 变量，  使用共享内存的程序在不该把Item类定义的情况下仍然可以正常运行（但是估计只适用于map，vector作为容器时不行）



老规矩，先看运行结果：

• 第一次运行创建共享内存的程序，可以正常创建；
• 第二次运行创建共享内存的程序，因为已经存在该名字的共享内存，所以抛出异常
• 第一次运行使用共享内存的程序，可以正常使用，并删除该共享内存
• 第一次运行使用共享内存的程序，因为已经删除了该共享内存，所以抛出异常

最后附上完整程序：
编译（注意需要修改boost库的路径）

boost_path="/home/colinliang/ThirdParty/boost_1_65_1"


#注意， -lrt必须放到最后！！！ 因为managed_shared_mem_use_map.cpp 要用到该库，，这个书写顺序会改变链接顺序！！！ 
#参见 https://*.com/questions/43052020/undefined-reference-to-shm-open-even-while-compiling-with-pthread-lrt
#It makes a difference where in the command you write this option; the linker searches and processes libraries and object files in the order they are specified. Thus, ‘foo.o -lz bar.o’ searches library ‘z’ after file foo.o but before bar.o. If bar.o refers to functions in ‘z’, those functions may not be loaded.
g++ -std=c++0x -L/lib   -I $boost_path managed_shared_mem_use_map.cpp -o exe_managed_shared_mem_use_map -pthread -lrt

g++ -std=c++0x -L/lib   -I $boost_path managed_shared_mem_use_map__read_existing.cpp -o exe_managed_shared_mem_use_map__read_existing -pthread -lrt

创建共享内存  managed_shared_mem_use_map.cpp：

/**  在共享内存中使用 boost 的map,  ---创建共享内存
 原始代码有个致命的错误——存储的Value中用来std::string!! 会导致segment fault
 * 代码来自： http://blog.csdn.net/nellson/article/details/50681103
 * 官方文档： http://www.boost.org/doc/libs/1_65_1/doc/html/interprocess.html
 *
 更复杂的例子，比如 map中嵌套vector， 以及 boost::unordered_map 的使用 等
 请参见 http://www.boost.org/doc/libs/1_65_1/doc/html/interprocess/allocators_containers.html#interprocess.allocators_containers.containers_explained.containers_of_containers

 * 需要添加的库：https://*.com/questions/7985236/c-boost-libraries-shared-memory-object-undefined-reference-to-shm-open
 * 		链接时需要添加 rt 库，方法为  g++ -L /lib -lrt
 */

//#include <boost/interprocess/shared_memory_object.hpp>
//#include <boost/interprocess/mapped_region.hpp>
#include <boost/interprocess/managed_shared_memory.hpp>
#include <boost/interprocess/allocators/allocator.hpp>
#include <boost/interprocess/containers/map.hpp>
#include <boost/interprocess/containers/vector.hpp>
#include <boost/interprocess/containers/string.hpp>

#include <functional>
#include <cstdlib>
#include <utility>
#include <sstream>
#include <stdio.h>
#include <stdlib.h>
#include <exception>
#include <sys/mman.h>
#include <sys/stat.h>
#include <fcntl.h>  
#include <string>
#include <iostream>

using namespace boost::interprocess;
//Typedefs of allocators and containers
typedef managed_shared_memory::segment_manager segment_manager_t;
typedef allocator<void, segment_manager_t> void_allocator;
typedef allocator<int, segment_manager_t> int_allocator;
typedef vector<int, int_allocator> int_vector;
typedef allocator<int_vector, segment_manager_t> int_vector_allocator;
typedef vector<int_vector, int_vector_allocator> int_vector_vector;
typedef allocator<char, segment_manager_t> char_allocator;
typedef basic_string<char, std::char_traits<char>, char_allocator> char_string;

using std::string;

class Item {
public:
	Item(const void_allocator& alloc, const char* name = "", int id = 0, int size = 0) :
			id(id), size(size), name(name, alloc) {
	}
	~Item() {
	}

	int id;
	int size;
	char_string name; //注意所有需要动态分配内存的变量，都只能用boost 的allocator进行内存分配
};

typedef char_string KeyType;
typedef Item MappedType;
typedef std::pair<const char_string, Item> ValueType;

typedef allocator<ValueType, managed_shared_memory::segment_manager> ShmemAllocator;

typedef map<KeyType, MappedType, std::less<KeyType>, ShmemAllocator> MyMap;

int main() {
	try {
		// init
		managed_shared_memory segment(create_only, "SharedMemory", 65536); //注意这里必须指定共享内存的大小

		const void_allocator alloc_inst(segment.get_segment_manager());

		MyMap * mymap = segment.construct < MyMap > ("MyMap")(std::less<KeyType>(), alloc_inst);
		MyMap * mymap2 = segment.construct < MyMap > ("MyMap2")(std::less<KeyType>(), alloc_inst); //可以构建两个，但名称不能一样，否则会产生异常boost::interprocess_exception::library_error

		KeyType key(alloc_inst);
		Item v(alloc_inst);
		for (int i = 0; i < 5; ++i) {
			key = (std::string("n") + std::to_string(i)).c_str();
			v.id = i * 10;
			v.size = -i;
			v.name = (std::string("n") + std::to_string(i)).c_str();

			mymap->insert(ValueType(key, v));
		}

		MyMap* mymap_for_use = segment.find < MyMap > ("MyMap").first;
		long int r = segment.find < MyMap > ("MyMap").second;
		printf("result of find map in shared-memory: %ld\n", r);

		printf("key-values in shared memory: \n");
		for (MyMap::iterator it = mymap_for_use->begin(); it != mymap_for_use->end(); it++) {
			const auto& item = it->second;
			printf("\tkey: %s, item.id: %d, item.size: %d, item.name: %s\n", it->first.c_str(), item.id, item.size,
					item.name.c_str());
		}

		//shared_memory_object::remove("SharedMemory");
	} catch (const std::exception & e) {
		printf("Exception:%s\n", e.what());
		//shared_memory_object::remove("SharedMemory");
	}

	return 0;

}

使用共享内存 managed_shared_mem_use_map__read_existing.cpp：

/**  在共享内存中使用 boost 的map,  ----使用已经存在的共享内存
 原始代码有个致命的错误——存储的Value中用来std::string!! 会导致segment fault
 * 代码来自： http://blog.csdn.net/nellson/article/details/50681103
 * 官方文档： http://www.boost.org/doc/libs/1_65_1/doc/html/interprocess.html
 *
 更复杂的例子，请参见http://www.boost.org/doc/libs/1_65_1/doc/html/interprocess/allocators_containers.html
 中的“Containers of containers”一节

 * 需要添加的库：https://*.com/questions/7985236/c-boost-libraries-shared-memory-object-undefined-reference-to-shm-open
 * 		链接时需要添加 rt 库，方法为  g++ -L /lib -lrt
 */
//#include <boost/interprocess/shared_memory_object.hpp>
//#include <boost/interprocess/mapped_region.hpp>
#include <boost/interprocess/managed_shared_memory.hpp>
#include <boost/interprocess/allocators/allocator.hpp>
#include <boost/interprocess/containers/map.hpp>
#include <boost/interprocess/containers/vector.hpp>
#include <boost/interprocess/containers/string.hpp>

#include <functional>
#include <cstdlib>
#include <utility>
#include <sstream>
#include <stdio.h>
#include <stdlib.h>
#include <exception>
#include <sys/mman.h>
#include <sys/stat.h>
#include <fcntl.h>  
#include <string>
#include <iostream>

using namespace boost::interprocess;
//Typedefs of allocators and containers
typedef managed_shared_memory::segment_manager segment_manager_t;
typedef allocator<void, segment_manager_t> void_allocator;
typedef allocator<int, segment_manager_t> int_allocator;
typedef vector<int, int_allocator> int_vector;
typedef allocator<int_vector, segment_manager_t> int_vector_allocator;
typedef vector<int_vector, int_vector_allocator> int_vector_vector;
typedef allocator<char, segment_manager_t> char_allocator;
typedef basic_string<char, std::char_traits<char>, char_allocator> char_string;

using std::string;

class Item {
public:
	Item(const void_allocator& alloc, const char* name = "", int id = 0, int size = 0) :
			id(id), size(size), name(name, alloc) {
	}
	~Item() {
	}

	int id;
	int size;
	char_string name; //注意所有需要动态分配内存的变量，都只能用boost 的allocator进行内存分配
};

typedef char_string KeyType;
typedef Item MappedType;
typedef std::pair<const char_string, Item> ValueType;

typedef allocator<ValueType, managed_shared_memory::segment_manager> ShmemAllocator;

typedef map<KeyType, MappedType, std::less<KeyType>, ShmemAllocator> MyMap;

int main() {
	try {
		//shared_memory_object::remove("SharedMemory");
		// init
		managed_shared_memory segment(open_only, "SharedMemory");

		MyMap* mymap_for_use = segment.find < MyMap > ("MyMap").first;
		long int r = segment.find < MyMap > ("MyMap").second;
		printf("result of find map in shared-memory: %ld\n", r);

		printf("key-values in shared memory: \n");
		for (MyMap::iterator it = mymap_for_use->begin(); it != mymap_for_use->end(); it++) {
			const auto& item = it->second;
			printf("\tkey: %s, item.id: %d, item.size: %d, item.name: %s\n", it->first.c_str(), item.id, item.size,
					item.name.c_str());
		}
		

		shared_memory_object::remove("SharedMemory");
	} catch (const std::exception & e) {
		printf("Exception:%s\n", e.what());
		shared_memory_object::remove("SharedMemory");
	}

	return 0;

}