semget - get set of semaphores
int semget(key_t key, int nsems, int semflg);
semget() returns the semaphore identifier associated with key.
A semaphore identifier and associated data structure and set
containing nsems semaphores are created for key if one of the
following is true:
key is equal to IPC_PRIVATE. This call creates a new identifier,
subject to available resources. The identifier is never returned
by another call to semget() until it has been released by a call
to semctl(). The identifier should be used among the calling
process and its descendents; however, it is not a requirement.
The resource can be accessed by any process having the proper
key does not already have a semaphore identifier associated with
it, and (semflg & IPC_CREAT) is ``true''.
Specific behavior can be requested by ORing the following masks into
IPC_CREAT: Create a semaphore identifier if one does not already
exist for key.
IPC_EXCL: If IPC_CREAT is specified and key already has a
semaphore identifier associated with it, return an error.
The low-order 9 bits of semflg are the semaphore operation permissions
which are defined in glossary(9).
Upon creation, the data structure associated with the new semaphore
identifier is initialized as follows:
In the operation-permission structure, sem_perm.cuid and
sem_perm.uid are set equal to the effective-user-ID of the
calling process, while sem_perm.cgid and sem_perm.gid are set to
the effective-group-ID of the calling process.
The low-order 9 bits of sem_perm.mode are set equal to the low-
order 9 bits of semflg.
sem_nsems is set equal to the value of nsems.
Hewlett-Packard Company - 1 - HP-UX Release 11i: November 2000
sem_otime is set equal to 0 and sem_ctime is set equal to the
The following call to semget() returns a semid associated with the key
returned by ftok("myfile", 'A'). If a semid associated with the key
does not exist, a new semid, set of 4 semaphores, and associated data
structure will be created. If a semid for the key already exists, the
semid is simply returned.
mysemid = semget (ftok("myfile",'A'), 4, IPC_CREAT | 0600);
Upon successful completion, a non-negative integer, namely a semaphore
identifier, is returned. Otherwise, a value of -1 is returned and
errno is set to indicate the error.
semget() fails if one or more of the following is true:
[EINVAL] nsems is either less than or equal to zero or
greater than the system-imposed limit.
[EACCES] A semaphore identifier exists for key, but
operation permission as specified by the low-order
9 bits of semflg would not be granted.
[EINVAL] A semaphore identifier exists for key, but the
number of semaphores in the set associated with it
is less than nsems, and nsems is not equal to
[ENOENT] A semaphore identifier does not exist for key and
(semflg & IPC_CREAT) is ``false''.
[ENOSPC] A semaphore identifier is to be created, but the
system-imposed limit on the maximum number of
allowed semaphore identifiers system wide would be
[EEXIST] A semaphore identifier exists for key but
((semflg&&&& IPC_CREAT) &&&&&&&& (semflg &&&& IPC_EXCL)) is
ipcrm(1), ipcs(1), semctl(2), semop(2), stdipc(3C).
semget(): SVID2, SVID3, XPG2, XPG3, XPG4
Hewlett-Packard Company - 2 - HP-UX Release 11i: November 2000