SEMGET(2) — HP-UX

NAME

semget − get set of semaphores

SYNOPSIS

#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/sem.h>

int semget (key, nsems, semflg)
key_t 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 are created for key if one of the following are true:

Key is equal to IPC_PRIVATE.

Key does not already have a semaphore identifier associated with it, and (semflg & IPC_CREAT) is “true”.

Upon creation, the data structure associated with the new semaphore identifier is initialized as follows:

In the operation-permission structure, sem_perm.cuid and sem_perm.uid are set equal to the effective-user-ID of the calling process, while sem_perm.cgid and sem_perm.gid are set to the effective-group-ID of the calling process.

The low-order 9 bits of sem_perm.mode are set equal to the low-order 9 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.

EXAMPLES

The following call to semget returns a semid associated with the key returned by ftok("myfile", ’A’). If a semid associated with the key does not exist, a new semid, set of 4 semaphores and associated data structure will be created. If a semid for the key already exists, the semid is simply returned.

int semid;

mysemid = semget (ftok("myfile",’A’), 4, IPC_CREAT | 0600);

ERRORS

Semget will fail 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 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 & 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.

[EEXIST] A semaphore identifier exists for key but ( (semflg & IPC_CREAT) & ( semflg & IPC_EXCL) ) is “true”.

RETURN VALUE

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.

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