semget(2) - NetBSD Manual Pages

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SEMGET(2)                 NetBSD 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.

     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 al-
                   ready 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 associ-
                   ated with key was found.


SEE ALSO

     semctl(2), semop(2)

NetBSD 1.4                      August 17, 1995                              1