belliottsmith commented on code in PR #4895:
URL: https://github.com/apache/cassandra/pull/4895#discussion_r3578239804
##########
src/java/org/apache/cassandra/metrics/ThreadLocalMetrics.java:
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@@ -374,26 +373,108 @@ static void recycleMetricId(int metricId)
lock.unlock();
}
- // there's no an obvious happens-before relation between
currentCounterValues[metricId] = 0 write we just did
- // and an initial read of the entry by a thread which updates the
reused metric
- // as a workaround we introduce a delay in recyling to provide the
write visibility in practice
- // even if it is not formally guaranteed by the JMM
- ScheduledExecutors.scheduledTasks.schedule(() -> {
+ freeMetricIdSetTracker.markAsFree(metricId);
+ }
+
+ @VisibleForTesting
+ static class FreeMetricIdSetTracker
+ {
+
+ private final Object freeMetricIdSetGuard = new Object();
+
+ private final BitSet freeMetricIdSet = new BitSet();
+
+ private final BitSet tickDelayedToFreeMetricIdSet = new BitSet();
+ private final BitSet tockDelayedToFreeMetricIdSet = new BitSet();
+
+ private BitSet delayedToFreeMetricIdSet = tickDelayedToFreeMetricIdSet;
+ private volatile boolean anythingToFree;
+
+ FreeMetricIdSetTracker()
+ {
+ this(true);
+ }
+
+ @VisibleForTesting
+ FreeMetricIdSetTracker(boolean scheduleTask)
+ {
+ if (scheduleTask)
+
ScheduledExecutors.scheduledTasks.scheduleAtFixedRate(this::triggerRecycling,
5, 5, TimeUnit.SECONDS);
Review Comment:
This is fine, but I generally prefer to only schedule when there is work to
do, which we can manage with a simple boolean or Future representing whether
work is scheduled, that we clear before we begin undertaking the recycling work?
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