HBASE-27437 TestHeapSize is flaky (apache#4841)

Signed-off-by: GeorryHuang <huangzhuoyue@apache.org>
(cherry picked from commit dad9a7d)

Conflicts:
	hbase-server/src/test/java/org/apache/hadoop/hbase/io/TestHeapSize.java

hbase-server/src/test/java/org/apache/hadoop/hbase/io/TestHeapSize.java

@@ -17,6 +17,8 @@
  */
 package org.apache.hadoop.hbase.io;
 
+import static org.hamcrest.MatcherAssert.assertThat;
+import static org.hamcrest.Matchers.lessThan;
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertTrue;
 
@@ -25,13 +27,16 @@
 import java.lang.management.RuntimeMXBean;
 import java.nio.ByteBuffer;
 import java.util.ArrayList;
+import java.util.Arrays;
 import java.util.LinkedList;
+import java.util.List;
 import java.util.Map;
 import java.util.TreeMap;
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.ConcurrentSkipListMap;
 import java.util.concurrent.CopyOnWriteArrayList;
 import java.util.concurrent.CopyOnWriteArraySet;
+import java.util.concurrent.TimeUnit;
 import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.concurrent.atomic.AtomicInteger;
 import java.util.concurrent.atomic.AtomicLong;
@@ -601,18 +606,30 @@ public void testObjectSize() throws IOException {
     }
   }
 
-  @Test
-  public void testAutoCalcFixedOverHead() {
-    Class[] classList = new Class[] { HFileContext.class, HRegion.class, BlockCacheKey.class,
-      HFileBlock.class, HStore.class, LruBlockCache.class, StoreContext.class };
-    for (Class cl : classList) {
-      // do estimate in advance to ensure class is loaded
-      ClassSize.estimateBase(cl, false);
-
-      long startTime = System.currentTimeMillis();
-      ClassSize.estimateBase(cl, false);
-      long endTime = System.currentTimeMillis();
-      assertTrue(endTime - startTime < 5);
+  private long calcFixedOverhead(List<Class<?>> classList) {
+    long overhead = 0;
+    for (Class<?> clazz : classList) {
+      overhead += ClassSize.estimateBase(clazz, false);
     }
+    return overhead;
+  }
+
+  @Test
+  public void testAutoCalcFixedOverhead() throws InterruptedException {
+    List<Class<?>> classList = Arrays.asList(HFileContext.class, HRegion.class, BlockCacheKey.class,
+      HFileBlock.class, HStore.class, LruBlockCache.class, StoreContext.class);
+    for (int i = 0; i < 10; i++) {
+      // warm up
+      calcFixedOverhead(classList);
+    }
+    long startNs = System.nanoTime();
+    long overhead = 0;
+    for (int i = 0; i < 100; i++) {
+      overhead += calcFixedOverhead(classList);
+    }
+    long costNs = System.nanoTime() - startNs;
+    LOG.info("overhead = {}, cost {} ns", overhead, costNs);
+    // the single computation cost should be less than 5ms
+    assertThat(costNs, lessThan(TimeUnit.MILLISECONDS.toNanos(5) * classList.size() * 100));
   }
 }