A marker interface for a factory that returns a
PortAggregator that acts as a barrier for a provided set of
input ports.
The barrier behaves as follows:
- It maintains, for each port, a slot that can contain a WireEnvelope.
- When a WireEnvelope is received on a port, the corresponding slot is filled with it. If the slot is not empty,
its content is replaced
- When all slots are filled, their contents are provided to the registered callback.
- The slots are cleared when the callback returns.