semget.2

来自「<B>Digital的Unix操作系统VAX 4.2源码</B>」· 2 代码 · 共 139 行

.\" SCCSID: @(#)semget.2	8.1	9/11/90
.TH semget 2
.SH Name
semget \- get set of semaphores
.SH Syntax
.nf
.ft B
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/sem.h>
.PP
.ft B
int semget (\fIkey, nsems, semflg\fP)
key_t \fIkey\fP;
int \fInsems, semflg\fP;
.fi
.SH Description
.NXR "semget system call"
.NXA "semget system call" "ftok subroutine"
.NXA "semget system call" "semctl system call"
.NXA "semget system call" "semop system call"
.NXR "semaphore" "getting"
The
.PN semget
system call
returns the semaphore identifier associated with
.IR key .
A semaphore identifier and associated data structure and set containing 
.I nsems
semaphores are created for
.IR key , 
if one of the following is true:
.IP \(bu 4
The
.I key
is equal to IPC_PRIVATE
.IP \(bu
The
.I key
does not already have a semaphore identifier associated with it, and
.RI ( semflg
& IPC_CREAT )
is true.
.PP
For further information, see 
.MS intro 2 .
.PP
Upon creation,
the data structure associated with the new semaphore identifier
is initialized as follows:
.IP \(bu 4
The
.BR sem_perm.cuid ,
.BR sem_perm.uid ,
.BR sem_perm.cgid
and
.B sem_perm.gid
are set equal to the effective user ID and effective group ID, respectively, of
the calling process.
.IP \(bu 4
The low-order nine bits of
.B sem_perm.mode
are set equal to the low-order nine bits of
.IR semflg .
.IP \(bu 4
The
.B sem_nsems 
is set equal to the value of
.I nsems.
.IP \(bu 4
The
.B sem_otime
is set equal to zero (0) and
.B sem_ctime 
is set equal to the current time.
.SH Return Values
Upon successful completion, a nonnegative integer, namely a semaphore
identifier, is returned.  Otherwise, a value of \-1 is returned and 
.I errno
is set to indicate the error.
.SH Diagnostics
.NXR "semget system call" "diagnostics"
The
.I semget
system call
fails if any of the following is true:
.TP 15
[EINVAL]
The
.I nsems
is either less than or equal 
to zero or greater than the system-imposed limit
.TP 15
[EACCES]
A semaphore identifier exists for
.IR key ,
but operation permission,
as specified by the low-order nine bits of
.I semflg
would not be granted. 
For further information, see 
.MS errno 2 .
.TP 15
[EINVAL]
A semaphore identifier exists for
.IR key ,
but the number of semaphores in the set associated with it is less than 
.I nsems
and
.I nsems
is not equal to zero. 
.TP 15
[ENOENT]
A semaphore identifier does not exist for
.I key 
and 
.RI ( semflg
& IPC_CREAT )
is false. 
.TP 15
[ENOSPC]
A semaphore identifier is to be created
but the system-imposed limit on the
maximum number of allowed semaphore
identifiers in the system would be exceeded.
.TP 15
[EEXIST]
A semaphore identifier exists for
.I key
but 
.RI (( semflg
& IPC_CREAT )
& 
.RI ( semflg
& IPC_EXCL ))
is true. 
.SH See Also
semctl(2), semop(2), ftok(3)