[GitHub] [helix] i3wangyi commented on a change in pull request #636: Simply and enhance the RebalanceLatencyGauge so it can be used in multi-threads.

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i3wangyi commented on a change in pull request #636: Simply and enhance the RebalanceLatencyGauge so it can be used in multi-threads.
URL: https://github.com/apache/helix/pull/636#discussion_r353444635
 
 

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 File path: helix-core/src/main/java/org/apache/helix/monitoring/metrics/implementation/RebalanceLatencyGauge.java
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 @@ -30,6 +31,8 @@
   private static final Logger LOG = LoggerFactory.getLogger(RebalanceLatencyGauge.class);
   private static final long VALUE_NOT_SET = -1;
   private long _lastEmittedMetricValue = VALUE_NOT_SET;
+  // Use threadlocal here so the start time can be updated and recorded in multi-threads.
+  private final ThreadLocal<Long> _startTime;
 
 Review comment:
   Wouldn't it be easier for each thread creating a new instance of RebalanceLatencyGauge, that you don't need to handle the concurrency complexities? It's more error-prone as we all know 
   But I do see the usage pattern is the one single instance RebalanceLatencyGauge will be long-lived in the memory - if it's desired, can we make sure the class usage always follows the singleton pattern? 
   

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