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This artifact provides a single jar that contains all classes required to use remote EJB and JMS, including all dependencies. It is intended for use by those not using maven, maven users should just import the EJB and JMS BOM's instead (shaded JAR's cause lots of problems with maven, as it is very easy to inadvertently end up with different versions on classes on the class path).

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/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements. See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership. The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied. See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */

package org.apache.activemq.artemis.utils;

import java.io.Serializable;
import java.util.function.Supplier;

import static org.apache.activemq.artemis.utils.Preconditions.checkNotNull;

public class Suppliers {

   /**
    * Returns a supplier which caches the instance retrieved during the first
    * call to {@code get()} and returns that value on subsequent calls to
    * {@code get()}. See:
    * memoization
    *
    * The returned supplier is thread-safe. The delegate's {@code get()}
    * method will be invoked at most once. The supplier's serialized form does
    * not contain the cached value, which will be recalculated when {@code get()}
    * is called on the reserialized instance.
    *
    * If {@code delegate} is an instance created by an earlier call to {@code
    * memoize}, it is returned directly.
    */
   public static  Supplier memoize(Supplier delegate) {
      return (delegate instanceof MemoizingSupplier)
            ? delegate
            : new MemoizingSupplier(checkNotNull(delegate));
   }

   private static class MemoizingSupplier implements Supplier, Serializable {
      final Supplier delegate;
      transient volatile boolean initialized;
      // "value" does not need to be volatile; visibility piggy-backs
      // on volatile read of "initialized".
      transient T value;

      MemoizingSupplier(Supplier delegate) {
         this.delegate = delegate;
      }

      @Override
      public T get() {
         // A 2-field variant of Double Checked Locking.
         if (!initialized) {
            synchronized (this) {
               if (!initialized) {
                  T t = delegate.get();
                  value = t;
                  initialized = true;
                  return t;
               }
            }
         }
         return value;
      }

      @Override
      public String toString() {
         return "Suppliers.memoize(" + delegate + ")";
      }

      private static final long serialVersionUID = 0;
   }


}