[ILUG] OT : Semaphore Key creation

[Bryan O'Donoghue]

ftok(), if I'm not mistaken, does *not* gaurantee, a unique key for the 
likes of semget();

What is the accepted methodology/wisdom for generating unique sem/shm keys?

Even something like

int a;
srand(time*getpid());
a=rand();
if(a<0)
     a*=-1;

key_t key=(key_t)a;

semget(key,1,0666 | whatever);

Has the potential for key collision if I'm not wrong.

Is there some sort of function I can call, which will list keys in use 
and from which I can then disjoin key id's against?

More to the point, if I do an "ipcs" and get.

------ Shared Memory Segments --------
key        shmid      owner      perms      bytes      nattch     status 


0x00000000 557059     beths     600        393216     2          dest 

0x00000000 589828     root      600        4331       0 


All with the same key, my thinking is it dones't really matter 'what' 
the key is, so long as the semid/shmid is unique... but I could be wrong.

I'm a bit confused here Batman, shouldn't the key be unique and not just 
the sem/shm id?

-- 
Bryan O'Donoghue
Embedded Software Engineer

Europlex Technologies Ltd
Clonshaugh Business & Technology Park
Dublin 17
Ireland

T:+353 (0) 1 2500500
F:+353 (0) 1 2500590
E:bryano at euoplex.ie
W:www.europlex.ie