ImmutableTimeStampedCache.java

  1. /* Contributed in the public domain.
  2.  * Licensed to CS Systèmes d'Information (CS) under one or more
  3.  * contributor license agreements.  See the NOTICE file distributed with
  4.  * this work for additional information regarding copyright ownership.
  5.  * CS licenses this file to You under the Apache License, Version 2.0
  6.  * (the "License"); you may not use this file except in compliance with
  7.  * the License.  You may obtain a copy of the License at
  8.  *
  9.  *   http://www.apache.org/licenses/LICENSE-2.0
  10.  *
  11.  * Unless required by applicable law or agreed to in writing, software
  12.  * distributed under the License is distributed on an "AS IS" BASIS,
  13.  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  14.  * See the License for the specific language governing permissions and
  15.  * limitations under the License.
  16.  */
  17. package org.orekit.utils;

  19. import java.util.ArrayList;
  20. import java.util.Collection;
  21. import java.util.Collections;
  22. import java.util.List;

  24. import org.apache.commons.math3.exception.util.LocalizedFormats;
  25. import org.apache.commons.math3.util.FastMath;
  26. import org.orekit.errors.OrekitException;
  27. import org.orekit.errors.OrekitMessages;
  28. import org.orekit.errors.TimeStampedCacheException;
  29. import org.orekit.time.AbsoluteDate;
  30. import org.orekit.time.ChronologicalComparator;
  31. import org.orekit.time.TimeStamped;

  33. /**
  34.  * A cache of {@link TimeStamped} data that provides concurrency through
  35.  * immutability. This strategy is suitable when all of the cached data is stored
  36.  * in memory. (For example, {@link org.orekit.time.UTCScale UTCScale}) This
  37.  * class then provides convenient methods for accessing the data.
  38.  *
  39.  * @author Evan Ward
  40.  * @param <T>  the type of data
  41.  */
  42. public class ImmutableTimeStampedCache<T extends TimeStamped>
  43.     implements TimeStampedCache<T> {

  45.     /**
  46.      * A single chronological comparator since instances are thread safe.
  47.      */
  48.     private static final ChronologicalComparator CMP = new ChronologicalComparator();

  50.     /**
  51.      * An empty immutable cache that always throws an exception on attempted
  52.      * access.
  53.      */
  54.     @SuppressWarnings("rawtypes")
  55.     private static final ImmutableTimeStampedCache EMPTY_CACHE =
  56.         new EmptyTimeStampedCache<TimeStamped>();

  58.     /**
  59.      * the cached data. Be careful not to modify it after the constructor, or
  60.      * return a reference that allows mutating this list.
  61.      */
  62.     private final List<T> data;

  64.     /**
  65.      * the size list to return from {@link #getNeighbors(AbsoluteDate)}.
  66.      */
  67.     private final int neighborsSize;

  69.     /**
  70.      * Create a new cache with the given neighbors size and data.
  71.      *
  72.      * @param neighborsSize the size of the list returned from
  73.      *        {@link #getNeighbors(AbsoluteDate)}. Must be less than or equal to
  74.      *        {@code data.size()}.
  75.      * @param data the backing data for this cache. The list will be copied to
  76.      *        ensure immutability. To guarantee immutability the entries in
  77.      *        {@code data} must be immutable themselves. There must be more data
  78.      *        than {@code neighborsSize}.
  79.      * @throws IllegalArgumentException if {@code neightborsSize > data.size()}
  80.      *         or if {@code neighborsSize} is negative
  81.      */
  82.     public ImmutableTimeStampedCache(final int neighborsSize,
  83.                                      final Collection<? extends T> data) {
  84.         // parameter check
  85.         if (neighborsSize > data.size()) {
  86.             throw OrekitException
  87.                 .createIllegalArgumentException(OrekitMessages.NOT_ENOUGH_CACHED_NEIGHBORS,
  88.                                                 data.size(), neighborsSize);
  89.         }
  90.         if (neighborsSize < 1) {
  91.             throw OrekitException
  92.                 .createIllegalArgumentException(LocalizedFormats.NUMBER_TOO_SMALL,
  93.                                                 neighborsSize, 0);
  94.         }

  96.         // assign instance variables
  97.         this.neighborsSize = neighborsSize;
  98.         // sort and copy data first
  99.         this.data = new ArrayList<T>(data);
  100.         Collections.sort(this.data, CMP);
  101.     }

  103.     /**
  104.      * private constructor for {@link #EMPTY_CACHE}.
  105.      */
  106.     private ImmutableTimeStampedCache() {
  107.         this.data = null;
  108.         this.neighborsSize = 0;
  109.     }

  111.     /** {@inheritDoc} */
  112.     public List<T> getNeighbors(final AbsoluteDate central)
  113.         throws TimeStampedCacheException {

  115.         // find central index
  116.         final int i = findIndex(central);

  118.         // check index in in the range of the data
  119.         if (i < 0) {
  120.             throw new TimeStampedCacheException(
  121.                                                 OrekitMessages.UNABLE_TO_GENERATE_NEW_DATA_BEFORE,
  122.                                                 this.getEarliest().getDate());
  123.         } else if (i >= this.data.size()) {
  124.             throw new TimeStampedCacheException(
  125.                                                 OrekitMessages.UNABLE_TO_GENERATE_NEW_DATA_AFTER,
  126.                                                 this.getLatest().getDate());
  127.         }

  129.         // force unbalanced range if necessary
  130.         int start = FastMath.max(0, i - (this.neighborsSize - 1) / 2);
  131.         final int end = FastMath.min(this.data.size(), start +
  132.                                                        this.neighborsSize);
  133.         start = end - this.neighborsSize;

  135.         // return list without copying
  136.         return Collections.unmodifiableList(this.data.subList(start, end));
  137.     }

  139.     /**
  140.      * Find the index, i, to {@link #data} such that {@code data[i] <= t} and
  141.      * {@code data[i+1] > t} if {@code data[i+1]} exists.
  142.      *
  143.      * @param t the time
  144.      * @return the index of the data at or just before {@code t}, {@code -1} if
  145.      *         {@code t} is before the first entry, or {@code data.size()} if
  146.      *         {@code t} is after the last entry.
  147.      */
  148.     private int findIndex(final AbsoluteDate t) {
  149.         // Guaranteed log(n) time
  150.         int i = Collections.binarySearch(this.data, t, CMP);
  151.         if (i == -this.data.size() - 1) {
  152.             // beyond last entry
  153.             i = this.data.size();
  154.         } else if (i < 0) {
  155.             // did not find exact match, but contained in data interval
  156.             i = -i - 2;
  157.         }
  158.         return i;
  159.     }

  161.     public int getNeighborsSize() {
  162.         return this.neighborsSize;
  163.     }

  165.     public T getEarliest() {
  166.         return this.data.get(0);
  167.     }

  169.     public T getLatest() {
  170.         return this.data.get(this.data.size() - 1);
  171.     }

  173.     /**
  174.      * Get all of the data in this cache.
  175.      *
  176.      * @return a sorted collection of all data passed in the
  177.      *         {@link #ImmutableTimeStampedCache(int, Collection) constructor}.
  178.      */
  179.     public List<T> getAll() {
  180.         return Collections.unmodifiableList(this.data);
  181.     }

  183.     /** {@inheritDoc} */
  184.     @Override
  185.     public String toString() {
  186.         return "Immutable cache with " + this.data.size() + " entries";
  187.     }

  189.     /**
  190.      * An empty immutable cache that always throws an exception on attempted
  191.      * access.
  192.      */
  193.     private static class EmptyTimeStampedCache<T extends TimeStamped> extends ImmutableTimeStampedCache<T> {

  195.         /** {@inheritDoc} */
  196.         @Override
  197.         public List<T> getNeighbors(final AbsoluteDate central)
  198.             throws TimeStampedCacheException {
  199.             throw new TimeStampedCacheException(
  200.                                                 OrekitMessages.NO_CACHED_ENTRIES);
  201.         };

  203.         /** {@inheritDoc} */
  204.         @Override
  205.         public int getNeighborsSize() {
  206.             return 0;
  207.         }

  209.         /** {@inheritDoc} */
  210.         @Override
  211.         public T getEarliest() {
  212.             throw OrekitException
  213.                 .createIllegalStateException(OrekitMessages.NO_CACHED_ENTRIES);
  214.         };

  216.         /** {@inheritDoc} */
  217.         @Override
  218.         public T getLatest() {
  219.             throw OrekitException
  220.                 .createIllegalStateException(OrekitMessages.NO_CACHED_ENTRIES);
  221.         }

  223.         /** {@inheritDoc} */
  224.         @Override
  225.         public List<T> getAll() {
  226.             return Collections.emptyList();
  227.         }

  229.         /** {@inheritDoc} */
  230.         @Override
  231.         public String toString() {
  232.             return "Empty immutable cache";
  233.         }

  235.     };

  237.     /**
  238.      * Get an empty immutable cache, cast to the correct type.
  239.      * @param <TS>  the type of data
  240.      * @return an empty {@link ImmutableTimeStampedCache}.
  241.      */
  242.     @SuppressWarnings("unchecked")
  243.     public static final <TS extends TimeStamped> ImmutableTimeStampedCache<TS> emptyCache() {
  244.         return (ImmutableTimeStampedCache<TS>) EMPTY_CACHE;
  245.     }

  247. }
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