rob05c edited a comment on issue #1739: Traffic Monitor CRConfig and 
monitoring.json polls aren't synchronized
URL: https://github.com/apache/trafficcontrol/issues/1739#issuecomment-446251341
 
 
   **Update**
   
   We have a PR to fix #1738 - PR #3104. But that PR does **not** fix this bug.
   The two bugs are:
   1. The `monitoring.json` data is not snapshotted.
   2. The Traffic Monitor doesn't ensure the versions of `monitoring.json` and 
`CRConfig` match.
   
   This case is for number 2.
   
   **How to fix**
   
   The code needs changed to request both the CRConfig and monitoring.json 
immediately one after the other. But that doesn't completely fix it, because 
there's still a small race, if someone were to Snapshot in-between the 
Monitor's requests.
   
   So, the requests actually need to happen in a loop, where each are 
requested, their timestamps are compared, and if one is older, it's fetched 
again, in a loop, until both timestamps match.
   
   The pseudocode looks something like:
   ```
   crConfig  = GetCRConfig()
   monitoring = GetMonitoring()
   for {
     if crConfig.SnapshotTime < monitoring.SnapshotTime {
       crConfig = GetCRConfig()
       continue
     }
     if monitoring.SnapshotTime < crConfig.SnapshotTime {
       monitoring = GetMonitoring()
       continue
     }
     break
   }
   ```
   

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