Originální popis anglicky:
shmget - get an XSI shared memory segment
Návod, kniha: POSIX Programmer's Manual
#include <sys/shm.h>
int shmget(key_t
key, size_t
size , int shmflg);
The
shmget() function operates on XSI shared memory (see the Base
Definitions volume of IEEE Std 1003.1-2001, Section 3.340,
Shared Memory Object). It is unspecified whether this function interoperates
with the realtime interprocess communication facilities defined in
Realtime .
The
shmget() function shall return the shared memory identifier
associated with
key.
A shared memory identifier, associated data structure, and shared memory segment
of at least
size bytes (see
<sys/shm.h>) are created for
key if one of the following is true:
- *
- The argument key is equal to IPC_PRIVATE.
- *
- The argument key does not already have a shared
memory identifier associated with it and ( shmflg &IPC_CREAT)
is non-zero.
Upon creation, the data structure associated with the new shared memory
identifier shall be initialized as follows:
- *
- The values of shm_perm.cuid, shm_perm.uid,
shm_perm.cgid, and shm_perm.gid are set equal to the
effective user ID and effective group ID, respectively, of the calling
process.
- *
- The low-order nine bits of shm_perm.mode are set
equal to the low-order nine bits of shmflg.
- *
- The value of shm_segsz is set equal to the value of
size.
- *
- The values of shm_lpid, shm_nattch,
shm_atime, and shm_dtime are set equal to 0.
- *
- The value of shm_ctime is set equal to the current
time.
When the shared memory segment is created, it shall be initialized with all zero
values.
Upon successful completion,
shmget() shall return a non-negative integer,
namely a shared memory identifier; otherwise, it shall return -1 and set
errno to indicate the error.
The
shmget() function shall fail if:
- EACCES
- A shared memory identifier exists for key but
operation permission as specified by the low-order nine bits of
shmflg would not be granted; see XSI Interprocess
Communication .
- EEXIST
- A shared memory identifier exists for the argument
key but ( shmflg &IPC_CREAT) &&( shmflg
&IPC_EXCL) is non-zero.
- EINVAL
- A shared memory segment is to be created and the value of
size is less than the system-imposed minimum or greater than the
system-imposed maximum.
- EINVAL
- No shared memory segment is to be created and a shared
memory segment exists for key but the size of the segment
associated with it is less than size and size is not 0.
- ENOENT
- A shared memory identifier does not exist for the argument
key and ( shmflg &IPC_CREAT) is 0.
- ENOMEM
- A shared memory identifier and associated shared memory
segment shall be created, but the amount of available physical memory is
not sufficient to fill the request.
- ENOSPC
- A shared memory identifier is to be created, but the
system-imposed limit on the maximum number of allowed shared memory
identifiers system-wide would be exceeded.
The following sections are informative.
None.
The POSIX Realtime Extension defines alternative interfaces for interprocess
communication. Application developers who need to use IPC should design their
applications so that modules using the IPC routines described in
XSI
Interprocess Communication can be easily modified to use the alternative
interfaces.
None.
None.
XSI Interprocess Communication ,
Realtime ,
shmat() ,
shmctl() ,
shmdt() ,
shm_open() ,
shm_unlink() ,
the Base Definitions volume of IEEE Std 1003.1-2001,
<sys/shm.h>
Portions of this text are reprinted and reproduced in electronic form from IEEE
Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable
Operating System Interface (POSIX), The Open Group Base Specifications Issue
6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. In the event of any discrepancy between
this version and the original IEEE and The Open Group Standard, the original
IEEE and The Open Group Standard is the referee document. The original
Standard can be obtained online at http://www.opengroup.org/unix/online.html
.
