semget(2)                                                         semget(2)




 NAME    [Toc]    [Back]
      semget - get set of semaphores

 SYNOPSIS    [Toc]    [Back]
      #include <sys/sem.h>

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

 DESCRIPTION    [Toc]    [Back]
      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
           permissions.

           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
      semflg.

           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 loworder
 9 bits of semflg.

           sem_nsems is set equal to the value of nsems.




 Hewlett-Packard Company            - 1 -   HP-UX 11i Version 2: August 2003






 semget(2)                                                         semget(2)




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

 EXAMPLES    [Toc]    [Back]
      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.

           int semid;

           mysemid = semget (ftok("myfile",'A'), 4, IPC_CREAT | 0600);

 RETURN VALUE    [Toc]    [Back]
      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.

 ERRORS    [Toc]    [Back]
      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
                          zero.

           [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
                          exceeded.

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

 SEE ALSO    [Toc]    [Back]
      ipcrm(1), ipcs(1), semctl(2), semop(2), stdipc(3C).

 STANDARDS CONFORMANCE    [Toc]    [Back]
      semget(): SVID2, SVID3, XPG2, XPG3, XPG4


 Hewlett-Packard Company            - 2 -   HP-UX 11i Version 2: August 2003