[CALCITE-6728] Introduce new methods to lookup tables and schemas ins…

…ide schemas

core/src/main/java/org/apache/calcite/schema/lookup/CachedLookup.java

@@ -16,12 +16,12 @@
  */
 package org.apache.calcite.schema.lookup;
 
+import org.apache.calcite.util.LazyReference;
 import org.apache.calcite.util.NameMap;
 
 import org.checkerframework.checker.nullness.qual.Nullable;
 
 import java.util.Set;
-import java.util.concurrent.atomic.AtomicReference;
 
 /**
  * This class can be used to make a snapshot of a lookups.
@@ -31,7 +31,7 @@
 public class CachedLookup<T> implements Lookup<T> {
 
   private final Lookup<T> delegate;
-  private AtomicReference<Lookup<T>> cachedDelegate = new AtomicReference<>();
+  private LazyReference<Lookup<T>> cachedDelegate = new LazyReference<>();
   private boolean enabled = true;
 
   public CachedLookup(Lookup<T> delegate) {
@@ -54,28 +54,23 @@ private Lookup<T> delegate() {
     if (!enabled) {
       return delegate;
     }
-    while (true) {
-      Lookup<T> cached = cachedDelegate.get();
-      if (cached != null) {
-        return cached;
-      }
-      NameMap<T> map = new NameMap<>();
-      for (String name : delegate.getNames(LikePattern.any())) {
-        T entry = delegate.get(name);
-        if (entry != null) {
-          map.put(name, delegate.get(name));
-        }
-      }
-      cached = new NameMapLookup<>(map);
-      if (cachedDelegate.compareAndSet(null, cached)) {
-        return cached;
+    return cachedDelegate.getOrCompute(() -> new NameMapLookup<>(loadNameMap()));
+  }
+
+  private NameMap<T> loadNameMap() {
+    NameMap<T> map = new NameMap<>();
+    for (String name : delegate.getNames(LikePattern.any())) {
+      T entry = delegate.get(name);
+      if (entry != null) {
+        map.put(name, delegate.get(name));
       }
     }
+    return map;
   }
 
   public void enable(boolean enabled) {
     if (!enabled) {
-      cachedDelegate.set(null);
+      cachedDelegate.reset();
     }
     this.enabled = enabled;
   }