SEMCTL(2) DOMAIN/IX Reference Manual (SYS5) SEMCTL(2)
NAME
semctl - semaphore control operations
USAGE
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/sem.h>
int semctl (semid, semnum, cmd, arg)
int semid, cmd;
int semnum;
union semun {
int val;
struct semid_ds *buf;
ushort *array;
} arg;
DESCRIPTION
Semctl provides semaphore control operations in the form of
commands, denoted cmd in USAGE above.
The following cmds are executed on the semaphore specified
by semid and semnum:
GETVAL Return the value of semval (see intro(2)).
{READ}
SETVAL Set the value of semval to arg.val. {ALTER}
When this command is successfully executed,
the semadj value corresponding to the speci-
fied semaphore in all processes is cleared.
GETPID Return the value of sempid. {READ}
GETNCNT Return the value of semncnt. {READ}
GETZCNT Return the value of semzcnt. {READ}
The following cmds return and set, respectively, every sem-
val in the set of semaphores.
GETALL Place semvals into array pointed to by
arg.array. {READ}
SETALL Set semvals according to the array pointed
to by arg.array. {ALTER} When this command
is successfully executed, the semadj values
corresponding to each specified semaphore in
all processes are cleared.
The following cmds are also available:
Printed 5/10/85 SEMCTL-1
SEMCTL(2) DOMAIN/IX Reference Manual (SYS5) SEMCTL(2)
IPC_STAT Place the current value of each member of
the data structure associated with semid
into the structure pointed to by arg.buf.
The contents of this structure are defined
in intro(2). {READ}
IPC_SET Set the value of the following members of
the data structure associated with semid to
the corresponding value found in the struc-
ture pointed to by arg.buf:
sem_perm.uid
sem_perm.gid
sem_perm.mode /* only low 9 bits */
This command can only be executed by a pro-
cess that has an effective user ID equal to
either that of super-user or to the value of
sem_perm.uid in the data structure associ-
ated with semid.
IPC_RMID Remove the semaphore identifier specified by
semid from the system and destroy the set of
semaphores and data structure associated
with it. This command can only be executed
by a process that has an effective user ID
equal to either that of super-user or to the
value of sem_perm.uid in the data structure
associated with semid.
RETURN VALUE
The value returned upon successful completion depends on
cmd.
GETVAL The value of semval.
GETPID The value of sempid.
GETNCNT The value of semncnt.
GETZCNT The value of semzcnt.
All others return a value of 0.
Otherwise, a value of -1 is returned and errno is set to
indicate the error.
ERRORS
Semctl will fail if one or more of the following is true:
[EINVAL] Semid is not a valid semaphore identifier.
[EINVAL] Semnum is less than zero or greater than
sem_nsems.
[EINVAL] Cmd is not a valid command.
[EACCES] Operation permission is denied to the calling
process (see intro(2)).
SEMCTL-2 Printed 5/10/85
SEMCTL(2) DOMAIN/IX Reference Manual (SYS5) SEMCTL(2)
[ERANGE] Cmd is SETVAL or SETALL and the value to
which semval is to be set is greater than the
system-imposed maximum.
[EPERM] Cmd is equal to IPC_RMID or IPC_SET and the
effective user ID of the calling process is
not equal to that of super-user and it is not
equal to the value of sem_perm.uid in the
data structure associated with semid.
[EFAULT] Arg.buf points to an illegal address.
RELATED INFORMATION
semget(2), semop(2)
Printed 5/10/85 SEMCTL-3