Message queue program

Messages are fetched from a queue by msgrcv. 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. Generally it is use to destroy message queue. Skip to content. Change Language. Active Oldest Votes. One short remark. I'm sure I'm not understanding something right, but aren't message queues supposed to be asynchronous? Why does the client barf an error and exits if the server isn't available?

As far as my probably wrong understanding goes, the whole point of message queues is to allow clients to write to unattended queues -- or else, what's the real difference between mqueues and FIFO? What am I misunderstanding here? Have you noticed I'm asking a lot of questions? The queue is always available through the API, the OS will keep it safe until someone consumes that data.

Show 2 more comments. There is something very wrong with your implementation. It is a terrible idea to pass pointers through mqueues, since a pointer is only valid in its own process, while mqueues are intended to be used between processes.

But in the end you are passing ints. This is just a synthetic example to show usage of mqueue. It demonstrates the contents of one integer moving through the queue into another integer where both are treated as buffers. Armardeep: sizeof a and sizeof b would be better than sizeof int. I would also argue that an even better approach which I would use in a production design would be to define a message type and its size. Show 1 more comment. Mureinik k 50 50 gold badges silver badges bronze badges.

Also, try to see the message queue state, by running command at different states of queue : ipcs -q For your linux system, you can know all the details of the IPC mechanisms and available queues etc, by using: ipcs -a Reference Blog. Community Bot 1 1 1 silver badge. In the next section, you will see the flags discussed in the earlier section. Then, we applied the condition to the name of the server and stored the messages in the queue buffer.

After this, at the time of storage, we ensured that the queues followed a first-come-based priority rule. At the end, the code displays a failure message if there are any errors received from the client-end. Finally, we exited the server to send the request to the client. We will now discuss the second file. The image displayed below is the code we used for the client-server communication. The code began by calling standard libraries and defining variable headers.

Then, we defined the strings and all types of data. After that, we declared the header of the queue to define the server queue name. Next, we defined the permission queues and message size inside the queue, along with the size of the message buffer the maximum size that could fit inside the queue. We will describe the queues and create a new client to receive the messages sent from the end of the server.

Then, we will call the flags and initialize them, and call the client-end function. It will exit the function in the case of an error.

The value is stored inside the buffer, and a request response is sent to the server.