[GitHub] markusthoemmes commented on a change in pull request #3272: improve loadbalancer's schedule algorithm

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

markusthoemmes commented on a change in pull request #3272: improve loadbalancer's schedule algorithm
URL: https://github.com/apache/incubator-openwhisk/pull/3272#discussion_r167427306
 
 

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 File path: core/controller/src/main/scala/whisk/core/loadBalancer/ContainerPoolBalancer.scala
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 @@ -345,7 +345,8 @@ object ContainerPoolBalancer extends LoadBalancerProvider {
         .find(_._3 < invokerBusyThreshold)
         .orElse(invokerProgression.find(_._3 < invokerBusyThreshold * 2))
         .orElse(invokerProgression.find(_._3 < invokerBusyThreshold * 3))
-        .orElse(invokerProgression.headOption)
+        .orElse(
+          if (invokerProgression.size == 0) None else invokerProgression.lift(Random.nextInt(invokerProgression.size)))
 
 Review comment:
   The extra check for `size == 0` is redundant I think, since `lift` will automatically bound-check anyway.
   
   It is **crucial** to use `ThreadLocalRandom` vs. `Random` because getting randomness is synchronized and thus will result in thread-contention.

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