RTEMS POSIX API User's Guide
Message queues are named objects similar to the pipes of POSIX. They are a means of communicating data between multiple processes and for passing messages among tasks and ISRs. Message queues can contain a variable number of messages from 0 to an upper limit that is user defined. The maximum length of the message can be set on a per message queue basis. Normally messages are sent and received from the message queue in FIFO order. However, messages can also be prioritized and a priority queue established for the passing of messages. Synchronization is needed when a task waits for a message to arrive at a queue. Also, a task may poll a queue for the arrival of a message.
The message queue descriptor mqd_t represents the message queue. It is
passed as an argument to all of the message queue functions.
RTEMS POSIX API User's Guide
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