NAME [Toc] [Back]
msgget - get message queue
SYNOPSIS [Toc] [Back]
int msgget(key_t key, int msgflg);
DESCRIPTION [Toc] [Back]
msgget() returns the message queue identifier associated with key.
A message queue identifier and associated message queue and data
structure are created for key if one of the following is true:
key is equal to IPC_PRIVATE. This call creates a new identifier,
subject to available resources. The identifier will never be
returned by another call to msgget() until it has been released
by a call to msgctl(). The identifier should be used among the
calling process and its descendents; however, it is not a
requirement. The resource can be accessed by any process having
the proper permissions.
key does not already have a message queue identifier associated
with it, and (msgflg & IPC_CREAT) is ``true''.
On creation of a new queue, queue sizes above 64Kbytes can only
be constructed when the application is compiled with the
__BIGMSGQUEUE_ENABLED flag defined either explicitly with a
#define in the source or with -D__BIGMSGQUEUE_ENABLED at compile
WARNING: Programs compiled on HP-UX revisions prior to 11i
Version 1 use old 16-bit msqid_ds structure fields (obtained via
IPC_STAT of the msgctl(2) system call) which can describe queue
sizes only up to 64KBytes. Care must be taken such that queues
shared with such programs are not made larger than 64KBytes
(i.e., that __BIGMSGQUEUE_ENABLED is not specified when compiling
the caller of msgget). Or, those existing programs should be
recompiled. Or, the system administrator should restrict the
MSGMNB kernel tunable parameter to 64KBytes or less.
Upon creation, the data structure associated with the new message
queue identifier is initialized as follows:
msg_perm.cuid, msg_perm.uid, msg_perm.cgid, and msg_perm.gid are
set equal to the effective user ID and effective group ID,
respectively, of the calling process.
The low-order 9 bits of msg_perm.mode are set equal to the loworder
9 bits of msgflg.
Hewlett-Packard Company - 1 - HP-UX 11i Version 2: August 2003
msg_qnum, msg_lspid, msg_lrpid, msg_stime, and msg_rtime are set
equal to 0.
msg_ctime is set equal to the current time.
msg_qbytes is set equal to the system limit.
RETURN VALUE [Toc] [Back]
Upon successful completion, a non-negative integer, namely a message
queue identifier, is returned. Otherwise, a value of -1 is returned
and errno is set to indicate the error.
ERRORS [Toc] [Back]
msgget() fails if one or more of the following is true:
[EACCES] A message queue identifier exists for key, but
operation permission as specified by the low-order 9
bits of msgflg would not be granted.
[ENOENT] A message queue identifier does not exist for key and
(msgflg & IPC_CREAT) is ``false''.
[ENOSPC] A message queue identifier is to be created but the
system-imposed limit on the maximum number of allowed
message queue identifiers system wide would be
[EEXIST] A message queue identifier exists for key but ((msgflg
& IPC_CREAT) && (msgflg & IPC_EXCL)) is ``true''.
SEE ALSO [Toc] [Back]
ipcrm(1), ipcs(1), msgctl(2), msgop(2), stdipc(3C).
STANDARDS CONFORMANCE [Toc] [Back]
msgget(): SVID2, SVID3, XPG2, XPG3, XPG4
Hewlett-Packard Company - 2 - HP-UX 11i Version 2: August 2003 [ Back ]