HDDS-10103. Simplified snapshotCache with just one ConcurrentHashMap.

hadoop-ozone/integration-test/src/test/java/org/apache/hadoop/ozone/om/TestSnapshotDeletingService.java

@@ -194,7 +194,6 @@ public void testMultipleSnapshotKeyReclaim() throws Exception {
     // /vol1/bucket2/bucket2snap1 has been cleaned up from cache map
     SnapshotCache snapshotCache = om.getOmSnapshotManager().getSnapshotCache();
     assertEquals(2, snapshotCache.size());
-    assertEquals(2, snapshotCache.getPendingEvictionListSize());
   }
 
   @SuppressWarnings("checkstyle:MethodLength")

hadoop-ozone/ozone-manager/src/main/java/org/apache/hadoop/ozone/om/snapshot/ReferenceCounted.java

@@ -25,7 +25,7 @@
 /**
  * Add reference counter to an object instance.
  */
-public class ReferenceCounted<T, U extends ReferenceCountedCallback>
+public class ReferenceCounted<T, U>
     implements AutoCloseable {
 
   /**
@@ -95,12 +95,6 @@ public long incrementRefCount() {
       long newValTotal = refCount.incrementAndGet();
       Preconditions.checkState(newValTotal > 0L,
           "Total reference count overflown");
-
-      if (refCount.get() == 1L) {
-        // ref count increased to one (from zero), remove from
-        // pendingEvictionList if added
-        parentWithCallback.callback(this);
-      }
     }
 
     return refCount.get();
@@ -131,11 +125,6 @@ public long decrementRefCount() {
       long newValTotal = refCount.decrementAndGet();
       Preconditions.checkState(newValTotal >= 0L,
           "Total reference count underflow");
-
-      if (refCount.get() == 0L) {
-        // ref count decreased to zero, add to pendingEvictionList
-        parentWithCallback.callback(this);
-      }
     }
 
     return refCount.get();