Still celebrating National IT Professionals Day with 3 months of free Premium Membership. Use Code ITDAY17

x
?
Solved

How can I tell when a second process has accessed shared memory?

Posted on 2009-04-09
1
Medium Priority
?
368 Views
Last Modified: 2013-12-03
Hello all,

I have a simple c++ program running in windows that creates a file mapping object, etc. to share some memory with a second process. How can I tell when some process has accessed the shared memory? Please see my code.
#define BUF_SIZE	256	
 
#include <stdio.h>
#include <string.h>
#include <sys/types.h>
#include <windows.h>
#include <conio.h>
#include <tchar.h>
#include <memory.h>
 
char szName[] = "Global\\MyFileMappingObject";
char message[] = "This will be shared";
 
int main()
{
	HANDLE hMapFile = CreateFileMapping(
		INVALID_HANDLE_VALUE,
		NULL,
		PAGE_READWRITE,
		0,
		BUF_SIZE,
		szName);
 
	LPCTSTR pBuf = (LPTSTR)MapViewOfFile(
		hMapFile,
		FILE_MAP_ALL_ACCESS,
		0,
		0,
		BUF_SIZE);
 
	CopyMemory((PVOID)pBuf, message, (strlen(message) * sizeof(TCHAR)));
 
	getch();
 
	UnmapViewOfFile(pBuf);
	CloseHandle(hMapFile);
	return 0;
}

Open in new window

0
Comment
Question by:ehensens
[X]
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
1 Comment
 
LVL 86

Accepted Solution

by:
jkr earned 2000 total points
ID: 24107788
You only can tell that for sure when both processes signal these events to each other. See also http://www.codeproject.com/KB/threads/sharedmemipc.aspx ("Interprocess Communication using Shared Memory"). E.g.
#include <sys/types.h>
#include <windows.h>
#include <conio.h>
#include <tchar.h>
#include <memory.h>
 
char szName[] = "Global\\MyFileMappingObject";
char message[] = "This will be shared";
 
 
HANDLE ConnectEvent ( LPCTSTR pszName)
{
 
   HANDLE hEvent   =   CreateEvent (   NULL,
                                       FALSE,
                                       FALSE,
                                       pszName
                                   );
 
   if  (   INVALID_HANDLE_VALUE    ==  hEvent)
       {
           if  (   ERROR_ALREADY_EXISTS    ==  GetLastError    ())
               {
                   hEvent  =   OpenEvent   (   SYNCHRONIZE,
                                               FALSE,
                                               pszName
                                           );
 
                   if  (   INVALID_HANDLE_VALUE    ==  hEvent)
                       {
 
                           return NULL;
                       }
               }
       }
 
   return hEvent;
}
 
int main()
{
        HANDLE hMapFile = CreateFileMapping(
                INVALID_HANDLE_VALUE,
                NULL,
                PAGE_READWRITE,
                0,
                BUF_SIZE,
                szName);
 
        LPCTSTR pBuf = (LPTSTR)MapViewOfFile(
                hMapFile,
                FILE_MAP_ALL_ACCESS,
                0,
                0,
                BUF_SIZE);
 
        HANDLE hEvent = ConnectEvent("Global\\MyFileMappingEvent");
 
        CopyMemory((PVOID)pBuf, message, (strlen(message) * sizeof(TCHAR)));
 
        // Signal to other process that data was set
        SetEvent(hEvent);
 
        getch();
 
        UnmapViewOfFile(pBuf);
        CloseHandle(hMapFile);
        return 0;
}
 
// other process
 
// ...
 
        HANDLE hEvent = ConnectEvent("Global\\MyFileMappingEvent");
 
        // Wait for other process to signal that data has been copied
        WaitForSingleObject(hEvent,INFINITE);
 
        // Process data
 
        // ...

Open in new window

0

Featured Post

Microsoft Certification Exam 74-409

Veeam® is happy to provide the Microsoft community with a study guide prepared by MVP and MCT, Orin Thomas. This guide will take you through each of the exam objectives, helping you to prepare for and pass the examination.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Article by: SunnyDark
This article's goal is to present you with an easy to use XML wrapper for C++ and also present some interesting techniques that you might use with MS C++. The reason I built this class is to ease the pain of using XML files with C++, since there is…
What my article will show is if you ever had to do processing to a listbox without being able to just select all the items in it. My software Visual Studio 2008 crystal report v11 My issue was I wanted to add crystal report to a form and show…
The viewer will learn how to clear a vector as well as how to detect empty vectors in C++.
The viewer will be introduced to the member functions push_back and pop_back of the vector class. The video will teach the difference between the two as well as how to use each one along with its functionality.

722 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question