[GitHub] [incubator-zipkin-brave] adriancole commented on a change in pull request #908: Fixes some edge cases around sampler resetting

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

adriancole commented on a change in pull request #908: Fixes some edge cases around sampler resetting
URL: https://github.com/apache/incubator-zipkin-brave/pull/908#discussion_r289582385
 
 

 ##########
 File path: brave/src/main/java/brave/sampler/RateLimitingSampler.java
 ##########
 @@ -55,14 +55,17 @@ public static Sampler create(int tracesPerSecond) {
     long updateAt = nextReset.get();
 
     long nanosUntilReset = -(now - updateAt); // because nanoTime can be negative
-    boolean shouldReset = nanosUntilReset <= 0;
-    if (shouldReset) {
-      if (nextReset.compareAndSet(updateAt, updateAt + NANOS_PER_SECOND)) {
-        usage.set(0);
-      }
+    if (nanosUntilReset <= 0) {
+      // Attempt to move into the next sampling interval.
+      // nanosUntilReset is now invalid regardless of race winner, so we can't sample based on it.
+      if (nextReset.compareAndSet(updateAt, updateAt + NANOS_PER_SECOND)) usage.set(0);
 
 Review comment:
   I think maybe the below is the easier way to get to the point (we should be working off "now"), I will also add a unit test so recursion worries float away.
   
   ```diff
   --- a/brave/src/main/java/brave/sampler/RateLimitingSampler.java
   +++ b/brave/src/main/java/brave/sampler/RateLimitingSampler.java
   @@ -74,7 +74,7 @@ public class RateLimitingSampler extends Sampler {
        if (nanosUntilReset <= 0) {
          // Attempt to move into the next sampling interval.
          // nanosUntilReset is now invalid regardless of race winner, so we can't sample based on it.
   -      if (nextReset.compareAndSet(updateAt, updateAt + NANOS_PER_SECOND)) usage.set(0);
   +      if (nextReset.compareAndSet(updateAt, now + NANOS_PER_SECOND)) usage.set(0);
    
          // recurse as it is simpler than resetting all the locals.
          // reset happens once per second, this code doesn't take a second, so no infinite recursion.
   ```

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