SEMGET(2) SEMGET(2)
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
associated 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
process.
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 and semcusec
are set equal to the current time.
Page 1 May 1989
SEMGET(2) SEMGET(2)
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
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 & IPCCREAT) 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.
[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 May 1989