Is a message queue bidirectional?

Question

Is it possible to send data to and fro between two processes from just a single message queue?

Answer 1

Yes, you could implement this bi-directionally, but there is a loss compared to using multiple queues.

Any process can append a message to the queue at any time, but there is a blocking state when serving messages from the queue ... other processes seeking to read their messages from the queue must wait for messages ahead of theirs to be served to the respective processes.

Answer 2

If the message queue you are using has a trigger can the trigger be changed dynamically?

If there is no trigger then yes the queue can be bidirectional as long as both processes can read the queue.