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Java Simplified. Extensions and Useful Constructs for the Java Platform. Codeprimate Elements (a.k.a. cp-elements) is a Java library and micro-framework used to simplify the development of software applications written in Java. Elements packages several APIs into one library in order to address various application concerns and aspects of software design and development collectively and conveniently. Elements is a highly simple, yet robust and proven library built on solid OO principles, software design patterns and best practices to effectively solve common and reoccurring problems in software development.

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/*
 * Copyright 2016 Author or Authors.
 *
 * Licensed 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.cp.elements.lang.support;

import org.cp.elements.lang.IdentifierSequence;
import org.cp.elements.lang.concurrent.ThreadSafe;

/**
 * The TimeBasedIdentifierSequence class is an implementation of the {@link IdentifierSequence} interface generating
 * unique, Long-typed identifiers based on time.  In particular, this implementation uses the System clock
 * and is Thread-safe.
 *
 * While this maybe useful for testing purposes, it should not be used in distributed systems where multiple application
 * or system components may generate ID's using different instances of this class in separate JVMs.
 * This is particularly important with respect to clock skew.
 *
 * @author John J. Blum
 * @see java.lang.Long
 * @see java.lang.System
 * @see org.cp.elements.lang.IdentifierSequence
 * @since 1.0.0
 */
@SuppressWarnings("unused")
@ThreadSafe
public class TimeBasedIdentifierSequence implements IdentifierSequence {

  private static long currentIdentifier = -1l;

  /**
   * Generates the next unique ID in sequence in a global context, across all instances of this class in the same JVM
   * (or rather, {@link ClassLoader}).
   *
   * @return the next unique, global Long ID in the sequence.
   * @see java.lang.System#nanoTime()
   */
  protected static synchronized long nextGlobalId() {
    long newIdentifier = System.nanoTime();

    while (newIdentifier <= currentIdentifier) {
      newIdentifier = System.nanoTime();
    }

    currentIdentifier = newIdentifier;

    return newIdentifier;
  }

  /**
   * Generates the next unique ID in sequence.
   *
   * @return the next unique Long ID in the sequence.
   * @see #nextGlobalId()
   */
  @Override
  public synchronized Long nextId() {
    return nextGlobalId();
  }

}