dimitarndimitrov commented on code in PR #17221:
URL: https://github.com/apache/kafka/pull/17221#discussion_r1773293797
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coordinator-common/src/test/java/org/apache/kafka/coordinator/common/runtime/HdrHistogramTest.java:
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@@ -172,4 +177,39 @@ public void testHistogramDataReset() {
assertEquals(numEventsInFirstCycle, hdrHistogram.count(now +
maxSnapshotAgeMs));
assertEquals(numEventsInSecondCycle, hdrHistogram.count(now + 1 +
maxSnapshotAgeMs));
}
+
+ @Test
+ public void testLatestHistogramRace() throws InterruptedException,
ExecutionException {
+ long maxSnapshotAgeMs = 10L;
+ long now = System.currentTimeMillis();
+ HdrHistogram hdrHistogram = new HdrHistogram(maxSnapshotAgeMs,
MAX_VALUE, 1);
+ ExecutorService countExecutor = Executors.newFixedThreadPool(2);
+ for (int i = 1; i < 10000; i++) {
+ int numEvents = 2;
+ for (int j = 0; j < numEvents; j++) {
+ hdrHistogram.record(i);
+ }
+ final long moreThanMaxAge = now + maxSnapshotAgeMs + 1;
+ now = moreThanMaxAge;
+ CountDownLatch latch = new CountDownLatch(1);
+ Callable<Long> countTask = () -> {
+ try {
+ assertTrue(latch.await(500, TimeUnit.MILLISECONDS));
+ return hdrHistogram.count(moreThanMaxAge);
+ } catch (InterruptedException e) {
+ throw new RuntimeException(e);
+ }
+ };
+ Future<Long> t1Future = countExecutor.submit(countTask);
+ Future<Long> t2Future = countExecutor.submit(countTask);
+ latch.countDown();
+ long t1Count = t1Future.get();
+ long t2Count = t2Future.get();
+ assertTrue(
+ numEvents == t1Count && numEvents == t2Count,
Review Comment:
> with this PR a call to latestHistogram() will always return a
MAX_AGE_SNAPSHOT worth of data (as it should)
A call to `latestHistogram()` will return the delta from the latest snapshot
if that latest snapshot is more than `maxSnapshotAgeMs` old, updating the
snapshot to that delta in the process. The delta however might be 10 years
worth of data if the last `latestHistogram()` call was 10 years ago, as that's
the only code path that can update the snapshot right now.
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