Multicast mechanism for actual causal ordering

A number of multicast algorithms have been proposed to guarantee potential causal ordering. In these mechanisms, the delivery of a message would be blocked waiting for the delivery of causally earlier messages, even though it may not actually have a causal relationship with these messages. This represents a higher latency cost than necessary. Our objective is to reduce the latency time of multicast message delivery. This can be achieved by reducing the number of messages that a multicast message has to wait for. We propose a mechanism in which the delivery of a message would only be blocked by the delivery of messages with which it has an actual causal relationship. The mechanism includes causality information, supplied by users, in the multicast messages. Receivers deliver messages to application processes according to this information. We introduce a programming construction, message blocks, to simplify the task of expressing causality. Simulation results are included and discussed in detail.