netudima commented on code in PR #4003:
URL: https://github.com/apache/cassandra/pull/4003#discussion_r2032099459
##########
src/java/org/apache/cassandra/metrics/DecayingEstimatedHistogramReservoir.java:
##########
@@ -855,4 +855,319 @@ public String toString()
return "[" + min + ',' + max + ']';
}
}
+
+ interface MetricCleaner
+ {
+ void clean();
+ }
+
+ private static class BucketsPhantomReference extends
PhantomReference<Object> implements MetricCleaner
+ {
+ private final MetricCleaner cleaner;
+
+ public BucketsPhantomReference(ReferenceQueue<? super Object> q,
MetricCleaner cleaner)
+ {
+ super(Thread.currentThread(), q);
+ this.cleaner = cleaner;
+ }
+
+ public void clean()
+ {
+ cleaner.clean();
+ }
+ }
+
+ /**
+ * Writes are exclusive to the thread-local buckets, so we can use a
single updater for all threads.
+ * Readers will see a consistent view of the buckets and could be blocked
for a while.
+ * <p>
+ * The class is aslso being tracked by a phantom reference queue to
release the accumulated buckets when the thread is dead.
+ */
+ protected class BucketsThreadLocal
+ {
+ // try to use int[] instead of long[] to reduce memory usage, and move
to the sum array when overflow
+ private final AtomicReference<DecayingArray> decayingRef;
+ private final long[] estimated;
+ private volatile boolean writing;
+
+ public BucketsThreadLocal(int size)
+ {
+ this.decayingRef = new AtomicReference<>(new DecayingArray(size,
decayingEstimatedBuckets.decayLandmark));
+ this.estimated = new long[size];
+ }
+
+ public void update(int index, long now)
+ {
+ // This is only called by the thread that owns the thread local,
so we don't need to worry about contention.
+ // Once the rescaling has occurred, we need to flush the values to
the decayingBucket and report that the values are no longer in use.
+ writing = true;
Review Comment:
so, in the current implementation we have 2 volatile writes vs 2 addAndGet
operations in the original one, without a contention they cost may be quite
similar...
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