semget(2) - NetBSD Manual Pages

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SEMGET(2)                 NetBSD System Calls Manual                 SEMGET(2)


NAME

     semget -- get set of semaphores


LIBRARY

     Standard C Library (libc, -lc)


SYNOPSIS

     #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.  If both the IPC_CREAT bit and
     the IPC_EXCL bit are set in semflg, and key has a semaphore set associ-
     ated with it already, the operation will fail.

     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:

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

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

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

     ·   sem_nsems is set to the value of nsems.

     ·   sem_ctime is set to the current time.

     ·   sem_otime is set to 0.


RETURN VALUES

     semget() returns a non-negative semaphore identifier if successful.  Oth-
     erwise, -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 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 is not set in semflg and no semaphore set
                        associated with key was found.


SEE ALSO

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


STANDARDS

     The semget system call conforms to X/Open System Interfaces and Headers
     Issue 5 (``XSH5'').


HISTORY

     Semaphores appeared in the first release of AT&T System V UNIX.

NetBSD 3.0.1                     May 13, 2004                     NetBSD 3.0.1