Prerequisite : Inter Process Communication
A message queue is a linked list of messages stored within the kernel and identified by a message queue identifier. A new queue is created or an existing queue opened by msgget().
New messages are added to the end of a queue by msgsnd(). Every message has a positive long integer type field, a non-negative length, and the actual data bytes (corresponding to the length), all of which are specified to msgsnd() when the message is added to a queue. Messages are fetched from a queue by msgrcv(). We don’t have to fetch the messages in a first-in, first-out order. Instead, we can fetch messages based on their type field.
All processes can exchange information through access to a common system message queue. The sending process places a message (via some (OS) message-passing module) onto a queue which can be read by another process. Each message is given an identification or type so that processes can select the appropriate message. Process must share a common key in order to gain access to the queue in the first place.  System calls used for message queues: - ftok(): is use to generate a unique key.
- msgget(): either returns the message queue identifier for a newly created message queue or returns the identifiers for a queue which exists with the same key value.
- msgsnd(): Data is placed on to a message queue by calling msgsnd().
- msgrcv(): messages are retrieved from a queue.
- msgctl(): It performs various operations on a queue. Generally it is use to destroy message queue.
MESSAGE QUEUE FOR WRITER PROCESS C` include <stdio.h> `` include <sys/ipc.h> `` include <sys/msg.h> `` define MAX 10 `struct mesg_buffer {
long mesg_type;
include <sys/ipc.h> 0
include <sys/ipc.h> `1` include <sys/ipc.h> `2` include <sys/ipc.h> 3
include <sys/ipc.h> `4` include <sys/ipc.h> `5
include <sys/ipc.h> `7
include <sys/ipc.h> 3
include <sys/msg.h> `0
include <sys/msg.h> 2
include <sys/msg.h> 3
include <sys/msg.h> `4
include <sys/msg.h> `6
include <sys/msg.h> `8
define MAX 10 0
define MAX 10 1
define MAX 10 2
define MAX 10 `3
define MAX 10 5
define MAX 10 `6
define MAX 10 8
define MAX 10 `9`struct`0
define MAX 10 0
define MAX 10 `1`struct`4`struct`5
`struct`9 MESSAGE QUEUE FOR READER PROCESS C` include <stdio.h> `` include <sys/ipc.h> `` include <sys/msg.h> `struct mesg_buffer {
long mesg_type;
include <sys/ipc.h> 0
include <sys/ipc.h> `1` include <sys/ipc.h> `2` include <sys/ipc.h> 3
include <sys/ipc.h> `4` include <sys/ipc.h> `5
include <sys/ipc.h> `7
include <sys/ipc.h> 3
include <sys/msg.h> `0
include <sys/msg.h> 2
include <sys/msg.h> 3
include <sys/msg.h> `4
include <sys/msg.h> `6long`7
define MAX 10 `9`long`9
define MAX 10 0
define MAX 10 `1`mesg_type; `3`mesg_type; `4`mesg_type; `5`mesg_type; `6
`struct`9 Output: Last Updated : 25 Nov, 2020 Like Article Save Article | 
