theoretical limit on message queue sizes

[aryan1]

Hi All,

Following function obtains the system-maintained structure for a message queue:

bool getMessageQueueStats(int mqId, struct msqid_ds* buf)
{
    if(msgctl(mqId, IPC_STAT, buf) == -1)
    {
        return false;
    }

    return true;
}

And following function simply resizes a message queue to a user-defined value, namely, "size":

bool resizeMessageQueue(int mqId, struct msqid_ds* buf, int size)
{
    /* Modify the message queue features */
    buf->msg_perm.uid = geteuid();
    buf->msg_perm.gid = getegid();
    buf->msg_perm.mode = 0660;
    buf->msg_qbytes = size; // The new size for the message queue

    if(msgctl(mqId, IPC_SET, buf) == -1)
    {
        return false;
    }

    return true;
}

My question is if there is a theoretical limit on user-defined message queue sizes.

To put in other words, is it possible to increase the default message queue size to any user-defined value as long as that certain value does not exceed the size of system's physical memory ?

By the way, I use 64-bit Ubuntu 9.04.

Thanks.

[treuss]

You can change the default message queue size in Linux by changing /proc/sys/kernel/msgmnb.

Example:

echo "4294967295" >/proc/sys/kernel/msgmnb