HP-UX Reference (11i v2 03/08) - 2 System Calls (vol 5)

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semctl(2) semctl(2)

or to the value of either sem_perm.uid

or sem_perm.cuid in the data struc-

ture associated with semid.

RETURN VALUE

Upon successful completion,

semctl() returns a value based on cmd as follows:

GETVAL The value of semval .

GETNCNT The value of semncnt .

GETZCNT The value of semzcnt .

GETPID The value of sempid .

All others return

If it fails, it returns

-1 and sets

errno to indicate the error.

ERRORS

semctl() fails, it sets errno to one of the following values:

[EACCES] Operation permission is denied to the calling process (see semaphore operation per-

missions in glossary (9).

[EFAULT] cmd is

SETVAL, GETALL, SETALL, IPC_SET,orIPC_STAT, and arg is an invalid

pointer.

[EINVAL] semid is not a valid semaphore identiﬁer.

[EINVAL] semnum is less than zero or greater than or equal

sem_nsems.

[EINVAL] cmd is not a valid command, or the command contains invalid parameters.

[EPERM] cmd is equal to

IPC_RMID or IPC_SET and the process does not have an effective

user ID equal to either that of superuser or to the value of either sem_perm.uid

or sem_perm.cuid in the data structure associated with semid.

[ERANGE] cmd is

SETVAL or SETALL and the value to which semval is to be set is greater

than the system imposed maximum.

EXAMPLES

The following call to

semctl() initializes the set of 4 semaphores to the values 0, 1, 0, and 1 respec-

tively. This example assumes the process has a valid semid representing a set of 4 semaphores as shown

in the semget (2) manual entry. For an example of performing "P" and "V" operations on the semaphores

below, refer to semop (2).

union semun {

int val;

struct semid_ds ∗buf;

ushort ∗array;

} arg;

ushort semarray[4];

semarray[0] = 0;

semarray[1] = 1;

semarray[2] = 0;

semarray[3] = 1;

arg.array = &semarray[0];

semctl (mysemid, 0, SETALL, arg);