semget

- get set of semaphores

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() function 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.

Return Values

Upon successful completion, a non-negative integer representing a semaphore identifier is returned. Otherwise, -1 is returned and errno is set to indicate the error.

Errors

The semget() function will fail if:

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

The nsems argument is either less than or equal to 0 or greater than the system-imposed limit. See NOTES.

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 0.

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 semaphores or semaphore identifiers system-wide would be exceeded. See NOTES.

Attributes

See attributes(5) for descriptions of the following attributes:

See Also

ipcrm(1), ipcs(1), rctladm(1M), Intro(2), semctl(2), semop(2), setrctl(2), ftok(3C), attributes(5), standards(5)

Notes

The system-imposed limit on the value of the nsems argument is the maintained on a per-process basis using the process.max-sem-nsems resource control.

The system-imposed limit on the number of semaphore identifiers is maintained on a per-project basis using the project.max-sem-ids resource control. The zone.max-sem-ids resource control limis the total number of semaphore identifiers that can be allocated by a zone.

See rctladm(1M) and setrctl(2) for information about using resource controls.