CODEWITHSUNDEEP
c
Abe
Abe

Reputation: 105

How to disconnect a single process from a shared memory object

So I have an assignment to create a library of functions that can create a posix shared memory table, add a record, delete a record and close the table. For the close_table function my prof wants it to only disconnect the current process calling close_table, so if there are two or more processes connect to the shared memory, only the one that called close_table will be disconnected. Looking at the different functions for working with posix shared memory it seems shm_unlink is the only thing that does something like that, except is deletes the shared memory object itself. is there a function that only disconnects only the process calling it?

/* Close connection to the given table.  This should only disconnect
 * the current process from the table.
 */
void close_table(table_t *tbl);

Upvotes: 3

Views: 582

Answers (1)

Andrew Henle
Andrew Henle

Reputation: 1

From the POSIX shm_open() documentation, the creation of the shared memory region is:

fd = shm_open("/myregion", O_CREAT | O_RDWR, S_IRUSR | S_IWUSR);
if (fd == -1)
    /* Handle error */;


if (ftruncate(fd, sizeof(struct region)) == -1)
    /* Handle error */;


/* Map shared memory object */


rptr = mmap(NULL, sizeof(struct region),
       PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);

To remove the mapping:

munmap( rptr, sizeof(struct region));

That's all that's needed.

You should have probably closed the file descriptor after calling mmap() as it's no longer needed or even very useful at that point.

Upvotes: 3

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