[Time] [Ordering Anomaly]

Explain in detail, what ordering the messaging applications (i.e. WhatsApp, Facebook Messenger) is using? (FCFS or casual order) Please state the references.

Ordering of events by logical time (1) User X sends a message 'Meeting' to users Y, Z, A User Y reads and sends 'Re: Meeting User Z reads X's and Y's messages and sends Re: Meeting User A could see all messages in the wrong order: Inbox: ltem From 23 24 25 Subject Re: Meeting Meeting Re: Meeting Messages from X, Y, and Z have time order in the real world If the clocks on X's, Y's, and Z's computers could be synchronized, each message could carry a timestamp based on the local computer's clock Messages could be displayed for A in the correct time order of the real world Since clocks cannot be synchronized perfectly, we may use logical time 15