mspanc
Synchronizing time between two processes NOT within cluster
Hello,
I am writing an app where I need to synchronize time between two processes, running on two nodes that are not within cluster (and they cannot, by design). I can’t use NTP daemon as I cannot assume anything about host OS configuration. So basically I need something like NTP-per-process or just generic NTP client/server implementation and I will wrap it. Any recommendations on how to do this properly erlang-way or about battle-proven ready-to-use libraries?
The problem I need to resolve is that basically both apps “tick” every 10ms, and send data to each other. There’s a certain time window for which the receiver waits for the data. I have found out that when using :timer.send_interval the timer skews and window moves and receiver starts dropping data as it is considering them arriving too late.
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Qqwy
What is the reason that you are using timers here? (especially using strict time windows).
Attempting to pretend like the laws of nature can be broken (here: that communication between two nodes can always happen instantly) will result in an hill-up battle when building algorithms.
If it is possible to use conflict-free replicated data types (CRDTs) for your application, I would definitely take a look at that instead.
Can you tell us more about your problem domain? There might be other approaches to circumvent the problems you’re having.
benwilson512
Yeah 100hz real time sync guarantees across a cloud network sounds like a problem I would want to avoid having.
Mandemus
You answered your own question in that you need to synch ticks not time. Similar to how RTS games such as Starcraft work under the hood, being turn based. Only, you won’t need the fixed point deterministic simulation part. 
You need to weight your timeout window in order to adjust for changing network latency. So you just need the delta between the last two ticks.
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