07-30-2003
Hmmm....you do have a point. I was getting CBYTES mixed up with QBYTES.
I agree, for the most part, QNUM = 0 and CBYTES != 0 is not consistent. But I can think of one exception where it might make sense. When you do your msgsnd, you are setting msgflg to zero. That means that IPC_NOWAIT is turned off. The msgsnd system call checks to see if this message would exceed some limits. This includes a check of the message queue you are using as well as some system wide limits. If a msgsnd would exceed a limit and it did not set IPC_NOWAIT, the msgsnd system call will suspend until it is safe to send the message. I don't know what state the message queue is in during this suspension. It could well be that CBYTES has been increased but QNUM has not yet been incremented.
This would explain why it works for a few hours and then locks up. Reproduce the error and then run "ipcs -qa" and compare the total messages queue resources in use against your kernel parameters. If this is the problem, you will need to increase the kernel parameters. Or you may have a message queue leak somewhere.
That is my only idea. If it's not that, I would next suspect a broken kernel. You might check for any appropiate patches.
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IPCS(1) BSD General Commands Manual IPCS(1)
NAME
ipcs -- report System V interprocess communication facilities status
SYNOPSIS
ipcs [-abcmopqstMQST] [-C system] [-N core]
DESCRIPTION
The ipcs program provides information on System V interprocess communication (IPC) facilities on the system.
The options are as follows:
-a Show the maximum amount of information possible when displaying active semaphores, message queues, and shared memory segments. (This
is shorthand for specifying the -b, -c, -o, -p, and -t options.)
-b Show the maximum allowed sizes for active semaphores, message queues, and shared memory segments. The ``maximum allowed size'' is
the maximum number of bytes in a message on a message queue, the size of a shared memory segment, or the number of semaphores in a
set of semaphores.
-c Show the creator's name and group for active semaphores, message queues, and shared memory segments.
-m Display information about active shared memory segments.
-o Show outstanding usage for active message queues, and shared memory segments. The ``outstanding usage'' is the number of messages in
a message queue, or the number of processes attached to a shared memory segment.
-p Show the process ID information for active semaphores, message queues, and shared memory segments. The ``process ID information'' is
the last process to send a message to or receive a message from a message queue, the process that created a semaphore, or the last
process to attach or detach a shared memory segment.
-q Display information about active message queues.
-s Display information about active semaphores.
-t Show access times for active semaphores, message queues, and shared memory segments. The access times is the time of the last con-
trol operation on an IPC object, the last send or receive of a message, the last attach or detach of a shared memory segment, or the
last operation on a semaphore.
-C system
Extract the name list from the specified system instead of the default ``/netbsd''.
-M Display system information about shared memory.
-N core
Extract values associated with the name list from the specified core instead of the default ``/dev/kmem''. and semaphores.
-Q Display system information about messages queues.
-S Display system information about semaphores.
-T Display system information about shared memory, message queues and semaphores. (This is shorthand for specifying the -M, -Q, and -S
options.)
If none of the -M, -m, -Q, -q, -S, -s, or -T options are specified, information about all active IPC facilities is listed.
RESTRICTIONS
System data structures may change while ipcs is running; the output of ipcs is not guaranteed to be consistent.
FILES
/dev/kmem default kernel memory
/netbsd default system name list
SEE ALSO
ipcrm(1), shmat(2), shmctl(2), shmdt(2), shmget(2)
AUTHORS
Thorsten Lockert <tholo@sigmasoft.com>
BUGS
This manual page is woefully incomplete, because it does not at all attempt to explain the information printed by ipcs.
BSD
March 21, 2004 BSD