problems with semget

ringerxyz · 02-13-2005, 08:54 PM

Hi everyone,
I have a question about the first parameter of the semget :key_t key,
if two process use the same key value,they will get the same semaphore ,and now if a third process happend to be have the same kye value,then it will use the same semaphore with the first and second process,is this right?
if this is right ,then how to guarantee that a semaphore is only used by the first and the second process?

jtshaw · 02-13-2005, 09:21 PM

Check out the semctl command. You can use that command to set the permissions for the semephore and all that good stuff.

Hko · 02-14-2005, 06:30 AM

Quote:

Originally posted by ringerxyz
if this is right ,then how to guarantee that a semaphore is only used by the first and the second process?

Yes, this is right. And it can be a problem when another process uses the same IPC-key, while it wasn't meant to connect to that same IPC-resource. Proper permissions can prevent that of course, but the third process will fail getting a semaphore in that case.

The library function ftok() is there to improve chances getting a IPC-key that is unique, but still it will not guarantee it.