Solved

Use of shared memory accross processes ..

Posted on 1999-01-05
2
212 Views
Last Modified: 2013-12-06
I am using shared memory in my application. The shared memory will be accessed by many processes. In the shared memory, I build simple linked lists. Assume that Process A is building this linked list and Process B
will read the linked list at a later point of time.
Consider Process A has built this :
         
            --------------       --------------
           |         |  .--|--->|         |  .--|-----
            --------------       --------------       |
                 Node 1              Node 2           -
                                                      -

My question is will Process B understand the pointer
stored in Node 1 (when it tries to traverse the linked list)? Because that pointer is virtual and
should be understood only by Process A.
0
Comment
Question by:srivatsa_v
2 Comments
 
LVL 84

Expert Comment

by:ozo
ID: 2008643
I'd make the pointers relative to the shared memory block.
0
 
LVL 3

Accepted Solution

by:
elfie earned 100 total points
ID: 2008644
A recommended way of doing is, put all your 'pointers' in a struct at the beginning of the shared memory. Then when building the shared memory, put the offset to the  start of the shared memory inside this struct.

Then for each program working with this shared memory you have to create a local copy inside your program that will contain the real pointers. Once connected to the shared memery you know the starting address of the SM. Then fill up your local copy of the struct of pointers.

When you're only workiing  on HP-UX you can put the pointers inside the shared memory, as the shared memory will have the same starting for all connecting programs.
When working on other platforms, the SM can received different addresses depending on the size(data/code) of the connect program. So for these OS's it needed that you have a local copy of the pointers.

So the most generic way is add a header to your SM, that contains the offset to each part inside the SM, and when connecting to the SM, fill a local struct with pointers, adding the offset the start address of the SM
0

Featured Post

Free Tool: SSL Checker

Scans your site and returns information about your SSL implementation and certificate. Helpful for debugging and validating your SSL configuration.

One of a set of tools we are providing to everyone as a way of saying thank you for being a part of the community.

Question has a verified solution.

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

Attention: This article will no longer be maintained. If you have any questions, please feel free to mail me. jgh@FreeBSD.org Please see http://www.freebsd.org/doc/en_US.ISO8859-1/articles/freebsd-update-server/ for the updated article. It is avail…
My previous tech tip, Installing the Solaris OS From the Flash Archive On a Tape (http://www.experts-exchange.com/articles/OS/Unix/Solaris/Installing-the-Solaris-OS-From-the-Flash-Archive-on-a-Tape.html), discussed installing the Solaris Operating S…
Learn several ways to interact with files and get file information from the bash shell. ls lists the contents of a directory: Using the -a flag displays hidden files: Using the -l flag formats the output in a long list: The file command gives us mor…
Learn how to find files with the shell using the find and locate commands. Use locate to find a needle in a haystack.: With locate, check if the file still exists.: Use find to get the actual location of the file.:

830 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