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.OrekitIllegalArgumentException;
  27. import org.orekit.errors.OrekitIllegalStateException;
  28. import org.orekit.errors.OrekitMessages;
  29. import org.orekit.errors.TimeStampedCacheException;
  30. import org.orekit.time.AbsoluteDate;
  31. import org.orekit.time.ChronologicalComparator;
  32. import org.orekit.time.TimeStamped;

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

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

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

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

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

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

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

  102.     /**
  103.      * private constructor for {@link #EMPTY_CACHE}.
  104.      */
  105.     private ImmutableTimeStampedCache() {
  106.         this.data = null;
  107.         this.neighborsSize = 0;
  108.     }

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

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

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

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

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

  138.     /**
  139.      * Find the index, i, to {@link #data} such that {@code data[i] <= t} and
  140.      * {@code data[i+1] > t} if {@code data[i+1]} exists.
  141.      *
  142.      * @param t the time
  143.      * @return the index of the data at or just before {@code t}, {@code -1} if
  144.      *         {@code t} is before the first entry, or {@code data.size()} if
  145.      *         {@code t} is after the last entry.
  146.      */
  147.     private int findIndex(final AbsoluteDate t) {
  148.         // Guaranteed log(n) time
  149.         int i = Collections.binarySearch(this.data, t, CMP);
  150.         if (i == -this.data.size() - 1) {
  151.             // beyond last entry
  152.             i = this.data.size();
  153.         } else if (i < 0) {
  154.             // did not find exact match, but contained in data interval
  155.             i = -i - 2;
  156.         }
  157.         return i;
  158.     }

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

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

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

  172.     /**
  173.      * Get all of the data in this cache.
  174.      *
  175.      * @return a sorted collection of all data passed in the
  176.      *         {@link #ImmutableTimeStampedCache(int, Collection) constructor}.
  177.      */
  178.     public List<T> getAll() {
  179.         return Collections.unmodifiableList(this.data);
  180.     }

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

  188.     /**
  189.      * An empty immutable cache that always throws an exception on attempted
  190.      * access.
  191.      */
  192.     private static class EmptyTimeStampedCache<T extends TimeStamped> extends ImmutableTimeStampedCache<T> {

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

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

  208.         /** {@inheritDoc} */
  209.         @Override
  210.         public T getEarliest() {
  211.             throw new OrekitIllegalStateException(OrekitMessages.NO_CACHED_ENTRIES);
  212.         };

  214.         /** {@inheritDoc} */
  215.         @Override
  216.         public T getLatest() {
  217.             throw new OrekitIllegalStateException(OrekitMessages.NO_CACHED_ENTRIES);
  218.         }

  220.         /** {@inheritDoc} */
  221.         @Override
  222.         public List<T> getAll() {
  223.             return Collections.emptyList();
  224.         }

  226.         /** {@inheritDoc} */
  227.         @Override
  228.         public String toString() {
  229.             return "Empty immutable cache";
  230.         }

  232.     };

  234.     /**
  235.      * Get an empty immutable cache, cast to the correct type.
  236.      * @param <TS>  the type of data
  237.      * @return an empty {@link ImmutableTimeStampedCache}.
  238.      */
  239.     @SuppressWarnings("unchecked")
  240.     public static final <TS extends TimeStamped> ImmutableTimeStampedCache<TS> emptyCache() {
  241.         return (ImmutableTimeStampedCache<TS>) EMPTY_CACHE;
  242.     }

  244. }
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