semget

SEMGET(2)                 OpenBSD Programmer's Manual                SEMGET(2)

NAME

     semget - get semaphore set

SYNOPSIS

     #include <sys/types.h>
     #include <sys/ipc.h>
     #include <sys/sem.h>

     int
     semget(key_t key, int nsems, int semflg);

DESCRIPTION

     The semget() system call returns the semaphore identifier associated with
     key.

     A new set containing nsems semaphores is created if either key is equal
     to IPC_PRIVATE, or key does not have a semaphore set associated with it
     and the IPC_CREAT bit is set in semflg.

     The access modes of the created semaphores is specified in semflg by
     OR'ing the following values:

           SEM_A        alter permission for owner
           SEM_R        read permission for owner

           SEM_A >> 3   alter permission for group
           SEM_R >> 3   read permission for group

           SEM_A >> 6   alter permission for other
           SEM_R >> 6   read permission for other

     If a new set of semaphores is created, the data structure associated with
     it (the semid_ds structure, see semctl(2)) is initialized as follows:

     o   sem_perm.cuid and sem_perm.uid are set to the effective UID of the
         calling process.

     o   sem_perm.gid and sem_perm.cgid are set to the effective GID of the
         calling process.

     o   sem_perm.mode is set to the lower 9 bits of semflg.

     o   sem_nsems is set to the value of nsems.

     o   sem_ctime is set to the current time.

     o   sem_otime is set to 0.

RETURN VALUES

     semget() returns a non-negative semaphore identifier if successful.
     Otherwise, -1 is returned and errno is set to reflect the error.

ERRORS

     [EACCES]           The caller has no permission to access a semaphore set
                        already associated with key.

     [EEXIST]           Both IPC_CREAT and IPC_EXCL are set in semflg, and a
                        semaphore set is already associated with key.

     [EINVAL]           nsems is less than or equal to 0 or greater than the
                        system limit for the number in a semaphore set.

                        A semaphore set associated with key exists, but has
                        fewer semaphores than the number specified in nsems.

     [ENOSPC]           A new set of semaphores could not be created because
                        the system limit for the number of semaphores or the
                        number of semaphore sets has been reached.

     [ENOENT]           IPC_CREAT was not set in semflg and no semaphore set
                        associated with key was found.

SEE ALSO

     semctl(2), semop(2), ftok(3)

OpenBSD 5.1                      May 31, 2007                      OpenBSD 5.1