semctl.2

来自「<B>Digital的Unix操作系统VAX 4.2源码</B>」· 2 代码 · 共 214 行

.\" SCCSID: @(#)semctl.2	8.1	9/11/90
.TH semctl 2
.SH Name
semctl \- semaphore control operations
.SH Syntax
.nf
.B #include <sys/types.h\fP>
.B #include <sys/ipc.h\fP>
.B #include <sys/sem.h\fP>
.PP
.B int semctl (\fIsemid, semnum, cmd, arg\fP)
.B int \fIsemid, cmd\fP;
.B int \fIsemnum\fP;
.B union \fIsemun\fP {
	\fIint val\fP;
	\fIstruct semid_ds *buf\fP;
	\fIushort array[]\fP;
} arg\fP;
.fi
.in \-8
.SH Description
.NXR "semctl system call"
.NXR "semaphore" "control operations"
.NXR "semctl system call" "semget system call"
.NXR "semctl system call" "semop system call"
The
.PN semctl
system call
provides a variety of semaphore control operations as specified by 
.IR cmd .
The following 
.IR cmd s
are executed with respect to the semaphore specified by
.I semid
and
.IR semnum :
.TP 15
GETVAL
Return the value of 
.IR semval .
For further information, see
.MS intro 2 .
.TP 15
SETVAL
Set the value of 
.I semval
to arg.val.  When this command is successfully
executed, the 
.I semadj
value corresponding
to the specified semaphore in all
processes is cleared.
.TP 15
GETPID
Return the value of
.IR sempid .
.TP 15
GETNCNT
Return the value of 
.IR semncnt . 
.TP 15
GETZCNT
Return the value of
.IR semzcnt . 
.PP
The following
.IR cmd s
return and set every 
.I semval
in the set of semaphores:
.NXR "semctl system call" "commands"
.TP 15
GETALL
Place 
.IR semval s 
into array pointed to by
.IR arg.array .
.TP 15
SETALL
Set 
.IR semval s 
according to the array pointed to by
.I arg.array
When this command is successfully executed,
the 
.I semadj
values corresponding
to each specified semaphore in all processes are cleared.
.PP
The following 
.IR cmd s
are also available:
.TP 15
IPC_STAT
Place the current value of each member of the data structure associated with 
.I semid 
into the  structure pointed to by
.IR arg.buf .
The contents of this structure are defined in 
.MS intro 2 .
.TP 15
IPC_SET
Set the value of the following members of the data structure associated with
.I semid 
to the corresponding value found in the structure pointed to by
.IR arg.buf :
.EX
sem_perm.uid
sem_perm.gid
sem_perm.mode /* only low 9 bits */
.EE
.PP
This command can only be executed by a process that has an effective 
user ID equal to superuser or to the values of
.B sem_perm.uid
or
.B sem_perm.cuid
in the data structure associated with
.IR semid .
.TP 15
IPC_RMID
Remove the semaphore identifier specified by 
.I semid
from the system and destroy the set
of semaphores and data structure associated
with it.
This 
.I cmd 
can only be executed by a process that has an effective user
ID equal to either that of superuser or to the value of
.B sem_perm.uid
in the data structure associated with
.IR semid .
.SH Return Values
Upon successful completion, the value returned depends on 
.IR cmd ,
as follows:
.TP 15
GETVAL
The value of
.IR semval .
.TP 15
GETPID
The value of
.IR sempid .
.TP 15
GETNCNT
The value of 
.IR semncnt .
.TP 15
GETZCNT
The value of 
.IR semzcnt .
.TP 15
All other
A value of 0.
.RE
.PP
Otherwise, a value of \-1 is returned and
.I errno
is set to indicate the error.
.SH Diagnostics
.NXR "semctl system call" "diagnostics"
The
.PN semctl
system call fails if any of the following is true:
.TP 15
[EINVAL]
The
.I semid
is not a valid semaphore identifier. 
.TP 15
[EINVAL]
The
.I semnum
is less than zero or greater than
.B sem_nsems.
.TP 15
[EINVAL]
The
.I cmd
is not a valid command. 
.TP 15
[EACCES]
Operation permission is denied to the calling process.
For further information, see 
.MS errno 2 . 
.TP 15
[ERANGE]
The
.I cmd
is SETVAL or SETALL,
and the value to which semval is to be set
is greater than the system imposed maximum. 
.TP 15
[EPERM]
The
.I cmd
is equal to IPC_RMID
or IPC_SET 
and the effective user ID of the calling
process is not equal to that of superuser
nor to the value of
.B sem_perm.uid
in the data structure associated with
.IR semid .
.TP 15
[EFAULT]
The
.I arg.buf
points to an illegal address. 
.SH See Also
errno(2), intro(2), semget(2), semop(2)