[GitHub] [druid] 599166320 commented on a diff in pull request #13286: PrometheusEmitter NullPointerException fix

[GitBox <gi...@apache.org>]

599166320 commented on code in PR #13286:
URL: https://github.com/apache/druid/pull/13286#discussion_r1008710907


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extensions-contrib/prometheus-emitter/src/main/java/org/apache/druid/emitter/prometheus/PrometheusEmitter.java:
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@@ -57,7 +58,7 @@ public class PrometheusEmitter implements Emitter
 
   private HTTPServer server;
   private PushGateway pushGateway;
-  private String identifier;
+  private volatile String identifier;

Review Comment:
   The existence of multiple threads calling emitMetric will modify the `identifier`. Even if the `identifier` is modified countless times, there will always be only one result, which is an `idempotent design`.
   Currently only the thread of `PrometheusPushGatewayEmitter` will read the value of `identifier`. In order to guarantee the visibility of the reading thread, I use volatile to decorate the `identifier`.
   
   In addition, there is an inefficient way to use LinkedBlockingQueue to achieve safe publishing. This is how `InfluxdbEmitter` is implemented.



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