semget —
get semaphore set
#include
<sys/sem.h>
int
semget(
key_t
key,
int
nsems,
int
semflg);
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.
The access modes of the created semaphores is specified in
semflg as a bitwise OR of zero or more of the
following values:
SEM_A alter permission for owner
SEM_R read permission for owner
SEM_A >> 3 alter permission for group
SEM_R >> 3 read permission for group
SEM_A >> 6 alter permission for other
SEM_R >> 6 read permission for other
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.
semget() returns a non-negative semaphore
identifier if successful. Otherwise, -1 is returned and
errno is set to reflect the error.
-
-
- [
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 or equal to 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
was not set in semflg and no semaphore
set associated with key was found.
semctl(2),
semop(2),
ftok(3)
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