semget(2) manual page
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semget - get set of semaphores
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/sem.h>
int semget(key_t key, int nsems, int semflg);
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 IPC_PRIVATE
.
- key does not already have a semaphore identifier associated with it, and
(semflg&IPC_CREAT
) is true.
On creation, the data structure associated with
the new semaphore identifier is initialized as follows:
- sem_perm.cuid, sem_perm.uid,
sem_perm.cgid, and sem_perm.gid are set equal to the effective user ID
and
effective group ID,
respectively, of the calling process.
- The access permission
bits of sem_perm.mode are set equal to the access permission bits of semflg.
- sem_nsems is set equal to the value of nsems.
- sem_otime is set equal to
0 and sem_ctime is set equal to the current time.
Upon successful
completion, a non-negative integer, namely a semaphore identifier, is returned;
otherwise, -1 is returned and errno is set to indicate the error.
semget()
fails if one or more of the following are true:
- 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.
- EEXIST
- A semaphore
identifier exists for key but both (semflg&IPC_CREAT
) and (semflg&IPC_EXCL
)
are both true.
- EINVAL
- nsems is either less than or equal to zero or greater
than the system-imposed limit.
- 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.
- 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.
ipcs(1)
, ipcrm(1)
, intro(2)
, semctl(2)
,
semop(2)
, stdipc(3C)
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