Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!yale!cmcl2!adm!news
From: TAYBENGH%NUSDISCS.BITNET@cunyvm.cuny.edu
Newsgroups: comp.unix.internals
Subject: shmat() & shmdt() questions.
Message-ID: <24482@adm.BRL.MIL>
Date: 13 Sep 90 02:07:38 GMT
Sender: news@adm.BRL.MIL
Lines: 40


        I have 3 questions regarding usage of shared memory:
        1) can a child process inherit shmid from parent? i.e. does the shmid
valid in the following program segment?

                shmid = shmget(..);
                if (fork() != 0)
                {       /* parent process */
                        parent_shm = shmat(shmid, (char *)0, 0);
                        /* do sth on parent_shm */
                        .....
                }
                else
                {       /* child process */
                        child_shm = shmat(shmid, (char *)0, 0);
                        /* do sth on child_shm */
                        .....
                }

        2) can a child inherit the virtual address return by shmat()?
           for eg:
                shmid = shmget(..);
                addr = shmat(.shmid, (char *)0, 0);
                if (fork() != 0)
                {
                        /* do sth on addr */
                        ...
                }
                else
                {
                        /* can child sth on addr ??? */
                        .....
                }

        3) if a process quit without shmdt() the shared memory it attached
to, will the OS detect and decrement the shm_nattch in structure sgmid_ds?

        Thanks a lot for the help.

- Beng Hang (email: taybengh@nusdiscs)