09-13-2006
Problem with msgget()
Hi,
I am having problem with msgget() function.
Here is the problem that I am having on Unix :
I have two processes sender and receiver. Sender generates queue (msgget()) with some key e.g. 938, for output.
Receiver reads from the same queue. i.e. receiver also tries to get queue id calling msgget() function and using same key, 938 that sender used.
But the qid that sender is receiving from msgget() function is 16777219 and receiver is getting different qid. Ideally it should get the same qid i.e. 16777219.
I tried to remove this queue using
ipcrm -q <qid>
And I tried to bring up sender with key as 338. But still it is building qid as such huge number and receiver is getting different qid.
Now I am able to read from this queue.
But still not sure whether this qid is correct or not
Please let me know how do I resove this.
Thanks,
Ashwini
Last edited by Ashwini; 09-14-2006 at 10:54 AM..
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LEARN ABOUT OPENSOLARIS
msgget
msgget(2) System Calls msgget(2)
NAME
msgget - get message queue
SYNOPSIS
#include <sys/msg.h>
int msgget(key_t key, int msgflg);
DESCRIPTION
The msgget() argument returns the message queue identifier associated with key.
A message queue identifier and associated message queue and data structure (see Intro(2)) are created for key if one of the following are
true:
o key is IPC_PRIVATE.
o key does not already have a message queue identifier associated with it, and (msgflg&IPC_CREAT) is true.
On creation, the data structure associated with the new message queue identifier is initialized as follows:
o msg_perm.cuid, msg_perm.uid, msg_perm.cgid, and msg_perm.gid are set to the effective user ID and effective group ID, respec-
tively, of the calling process.
o The low-order 9 bits of msg_perm.mode are set to the low-order 9 bits of msgflg.
o msg_qnum, msg_lspid, msg_lrpid, msg_stime, and msg_rtime are set to 0.
o msg_ctime is set to the current time.
o msg_qbytes is set to the system limit. See NOTES.
RETURN VALUES
Upon successful completion, a non-negative integer representing a message queue identifier is returned. Otherwise, -1 is returned and errno
is set to indicate the error.
ERRORS
The msgget() function will fail if:
EACCES A message queue identifier exists for key, but operation permission (see Intro(2)) as specified by the low-order 9 bits of msgflg
would not be granted.
EEXIST A message queue identifier exists for key but (msgflg&IPC_CREAT) and (msgflg&IPC_EXCL) are both true.
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 identi-
fiers system wide would be exceeded. See NOTES.
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
+-----------------------------+-----------------------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+-----------------------------+-----------------------------+
|Interface Stability |Standard |
+-----------------------------+-----------------------------+
SEE ALSO
rctladm(1M), Intro(2), msgctl(2), msgrcv(2), msgsnd(2), setrctl(2), ftok(3C), attributes(5), standards(5)
NOTES
The system-defined limit used to initialize msg_qbytes is the minimum enforced value of the calling process's process.max-msg-qbytes
resource control.
The system-imposed limit on the number of message queue identifiers is maintained on a per-project basis using the project.max-msg-ids
resource control. The zone.max-msg-ids resource control restricts the total amount of message queue identifiers that can be allocated by a
zone.
See rctladm(1M) and setrctl(2) for information about using resource controls.
SunOS 5.11 14 Aug 2006 msgget(2)