SEMGET(2-SysV)      RISC/os Reference Manual       SEMGET(2-SysV)



NAME
     semget - get set of semaphores

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

     int semget (key, nsems, semflg)
     keyt 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 IPCPRIVATE.

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

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

          semperm.cuid, semperm.uid, semperm.cgid, and
          semperm.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 semperm.mode are set equal to
          the low-order 9 bits of semflg.

          semnsems is set equal to the value of nsems.

          semotime is set equal to 0 and semctime is set equal
          to the current time.

ERRORS
     semget fails if one or more of the following are 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 [see intro(2)] as speci-
                    fied by the low-order 9 bits of semflg would
                    not be granted.

     [EINVAL]       A semaphore identifier exists for key, but



                         Printed 1/15/91                   Page 1

SEMGET(2-SysV)      RISC/os Reference Manual       SEMGET(2-SysV)



                    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 & IPCCREAT) is ``false''.

     [ENOSPC]       A semaphore identifier is to be created but
                    the system-imposed limit on the maximum
                    number of allowed semaphore identifiers sys-
                    tem wide would be exceeded.

     [ENOSPC]       A semaphore identifier is to be created but
                    the system-imposed limit on the maximum
                    number of allowed semaphores system wide
                    would be exceeded.

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

SEE ALSO
     intro(2), semctl(2), semop(2).

DIAGNOSTICS
     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.



























 Page 2                  Printed 1/15/91