The first call creates the message queue with the optional perms (default:
msg_get_queue() returns an id that can be used to access the System V message queue with the given key. The first call creates the message queue with the optional perms (default: 0666). A second call to msg_get_queue() for the same key will return a different message queue identifier, but both identifiers access the same underlying message queue. If the message queue already exists, the perms will be ignored.