PolyM is a very simple C++ message queue intended for inter-thread communication. There are three major requirement driving the design of PolyM:

• The design should be simple and lightweight
• The design should support delivering any kind of data as the message payload
• There should be no copies made of the message payload data when passing the message through the queue

PolyM (Polymorphic Message Queue) fulfills these requirements by usage of C++ move semantics.

When a message with payload data (PolyM::DataMsg<PayloadType>) is created, the payload is allocated from the heap. When the message is put to the queue, it is moved there with so called "virtual move constructor". The virtual move constructor is what enables the polymorphism of the message queue: any message type derived from the base PolyM::Msg type can be moved to the queue. When a message is read from the queue, it is moved out from the queue to be the responsibility of the receiver.

All the message types are movable, but not copyable. Once the message is put to the queue, the sender cannot access the message data anymore. A message always has a single owner, and on send-receive scenario, the ownership is transferred

Sender -> Queue -> Receiver

PolyM supports two kinds of messaging patterns:

• One way
  • Messages are put to the queue with PolyM::Queue::put(). put() will return immediately.
  • Messages are read from the queue with PolyM::Queue::get(). get() will block until there is at least one message available in the queue (or until timeout occurs, if specified).
• Request-response
  • A request is made with PolyM::Queue::request(). request() will block until a response is given. The request message can be read from the queue just as any other message with get().
  • A response is given with PolyM::Queue::respondTo(). respondTo() will return immediately.