semget(2) — sys5



SEMGET(2)       DOMAIN/IX Reference Manual (SYS5)       SEMGET(2)



NAME
     semget - get set of semaphores

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

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

DESCRIPTION
     Semget returns the semaphore identifier associated with key.

     A semaphore identifier and associated data structure and set
     containing nsems semaphores (see intro(2)) are created for
     key if one of the following is true:

          Key is equal to IPC_PRIVATE.

          Key does not already have a semaphore identifier asso-
          ciated with it, and (semflg & IPC_CREAT) is ``true''.

     Upon creation, the data structure associated with the new
     semaphore identifier is initialized as follows:

          Sem_perm.cuid, sem_perm.uid, sem_perm.cgid, and
          sem_perm.gid are set equal to the effective user ID and
          effective group ID, respectively, of the calling pro-
          cess.

          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.

          Sem_otime is set equal to 0 and sem_ctime is set equal
          to the current time.

RETURN VALUE
     Semget returns a semaphore identifier, a non-negative
     integer, upon successful completion.  Otherwise, it returns
     a value of -1 and sets errno to indicate the error.

ERRORS
     Semget will fail 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



Printed 5/10/85                                          SEMGET-1



SEMGET(2)       DOMAIN/IX Reference Manual (SYS5)       SEMGET(2)



                    operation permission (see intro(2)) as speci-
                    fied by the low-order 9 bits of semflg cannot
                    be granted.

     [EINVAL]       A semaphore identifier exists for key, but
                    the number of semaphores in the set associ-
                    ated with it is less than nsems and nsems is
                    not equal to zero.

     [ENOENT]       A semaphore identifier does not exist for key
                    and (semflg & IPC_CREAT) is ``false''.

     [ENOSPC]       Creating a new semaphore identifier would
                    exceed the system-imposed limit on the max-
                    imum number of semaphore identifiers allowed
                    on the system.

     [EEXIST]       A semaphore identifier exists for key but (
                    (semflg & IPC_CREAT) and ( semflg & IPC_EXCL)
                    ) is ``true''.

RELATED INFORMATION
     semctl(2), semop(2)
































SEMGET-2                                          Printed 5/10/85

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