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[sri_shaiva]

Actually I dint understand allocation and freeing of memory in message queue.
The sender with message id sends message and receiver receives
and uses msgctl()-->to free the memory.

Now the quesiotn whct is freeing here ?Is it dynamic?Then it shud have malloc/calloc when allocating?But I dont see any thing here.

Where from the memory is allocated and where it is freed?

Please some one help me thanks in advance

[Rubberman]

Huh? The commands available for msgctl() are IPC_STAT, IPC_SET, IPC_RMID, IPC_INFO, MSG_INFO, and MSG_STAT. The only one that really manipulates kernel memory structurs is IPC_SET. You can change the maximum number of bytes allowed in a queue, but a couple of caveates here. One is that you need to have the appropriate privileges. Two is that if you increase the msg_qbytes field in the msqid_ds structure, it will only take effect when you create a new queue. It doesn't affect current queues as far as I know.

So, you have to manage your own memory as far as local buffers are concerned. The queue code in the kernel handles kernel allocation needs. When you send a message, it is copied by the kernel code into the kernel message structures. When you receive a message, you provide a pointer to a message structure of your own. The kernel code copies the kernel message data received into that buffer.

[Rubberman]

You may also want to review the mq_overview man page for more informatioon: man mq_overview