managed_shared_memory.construct造成的性能损失

boost中的IPC进程间通信非常好用，可以直接在共享内存上创建对象，相当于new分配器，实测发现它的分配算法还是有点耗时。第一个测试代码仅仅分配一次，然后频繁的复制，每秒钟可以复制4200次左右。

// HelloBoostIPC.cpp : Defines the entry point for the console application.

//

#include "stdafx.h"

#include <boost/interprocess/managed_shared_memory.hpp>

#include <boost/interprocess/sync/scoped_lock.hpp>

#include <cstdlib> //std::system

#include <cstddef>

#include <cassert>

#include <utility>

#include <string>

#include <Windows.h>

using namespace std;

using namespace boost;

using namespace boost::interprocess;

char dummy[1280*720*3];

class VideoFrame

{

public:

	int width;

	int height;

	boost::interprocess::interprocess_mutex mutex;

	char data[1280*720*3];

};

int _tmain(int argc, _TCHAR* argv[])

{

	int begin, end, n=0;

	struct shm_remove

	{

		shm_remove() { shared_memory_object::remove("MySharedMemory"); }

		~shm_remove(){ shared_memory_object::remove("MySharedMemory"); }

	} remover;

	managed_shared_memory segment(create_only, "MySharedMemory", sizeof(VideoFrame)*24);

	VideoFrame *frame = segment.construct<VideoFrame>("frame")();

	while(true)

	{

		if(n==0)

		{

			begin = ::GetTickCount();

		}

		frame->width = 1280;

		frame->height = 720;

		scoped_lock<interprocess_mutex> lock(frame->mutex);

		memcpy(frame->data, dummy, sizeof(dummy));

		n++;

		if(n==1000)

		{

			end = ::GetTickCount();

			float t = (end-begin)/1000.0f;

			int rate = (int)(1000/t);

			printf("write rate=%d\r\n", rate);

			n = 0;

		}

	}

	segment.destroy<VideoFrame>("frame");

	return 0;

}

如果更换成在循环内部分配内存，再释放，则复制频率下降到3200左右。因此在设计大数据量复制的应用程序时，最好不要频繁创建对象和析构对象，这点和进程内的程序开发是一致的。