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;
  23. import java.util.stream.Stream;

  25. import org.hipparchus.exception.LocalizedCoreFormats;
  26. import org.hipparchus.util.FastMath;
  27. import org.orekit.errors.OrekitIllegalArgumentException;
  28. import org.orekit.errors.OrekitIllegalStateException;
  29. import org.orekit.errors.OrekitMessages;
  30. import org.orekit.errors.TimeStampedCacheException;
  31. import org.orekit.time.AbsoluteDate;
  32. import org.orekit.time.ChronologicalComparator;
  33. import org.orekit.time.TimeStamped;

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

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

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

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

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

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

  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(OrekitMessages.UNABLE_TO_GENERATE_NEW_DATA_BEFORE,
  120.                                                 this.getEarliest().getDate());
  121.         } else if (i >= this.data.size()) {
  122.             throw new TimeStampedCacheException(OrekitMessages.UNABLE_TO_GENERATE_NEW_DATA_AFTER,
  123.                                                 this.getLatest().getDate());
  124.         }

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

  132.         // return list without copying
  133.         return this.data.subList(start, end).stream();
  134.     }

  136.     /**
  137.      * Find the index, i, to {@link #data} such that {@code data[i] <= t} and
  138.      * {@code data[i+1] > t} if {@code data[i+1]} exists.
  139.      *
  140.      * @param t the time
  141.      * @return the index of the data at or just before {@code t}, {@code -1} if
  142.      *         {@code t} is before the first entry, or {@code data.size()} if
  143.      *         {@code t} is after the last entry.
  144.      */
  145.     private int findIndex(final AbsoluteDate t) {
  146.         // Guaranteed log(n) time
  147.         int i = Collections.binarySearch(this.data, t, CMP);
  148.         if (i == -this.data.size() - 1) {
  149.             // beyond last entry
  150.             i = this.data.size();
  151.         } else if (i < 0) {
  152.             // did not find exact match, but contained in data interval
  153.             i = -i - 2;
  154.         }
  155.         return i;
  156.     }

  158.     public int getNeighborsSize() {
  159.         return this.neighborsSize;
  160.     }

  162.     public T getEarliest() {
  163.         return this.data.get(0);
  164.     }

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

  170.     /**
  171.      * Get all of the data in this cache.
  172.      *
  173.      * @return a sorted collection of all data passed in the
  174.      *         {@link #ImmutableTimeStampedCache(int, Collection) constructor}.
  175.      */
  176.     public List<T> getAll() {
  177.         return Collections.unmodifiableList(this.data);
  178.     }

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

  186.     /**
  187.      * An empty immutable cache that always throws an exception on attempted
  188.      * access.
  189.      */
  190.     private static class EmptyTimeStampedCache<T extends TimeStamped> extends ImmutableTimeStampedCache<T> {

  192.         /** {@inheritDoc} */
  193.         @Override
  194.         public Stream<T> getNeighbors(final AbsoluteDate central) {
  195.             throw new TimeStampedCacheException(OrekitMessages.NO_CACHED_ENTRIES);
  196.         }

  198.         /** {@inheritDoc} */
  199.         @Override
  200.         public int getNeighborsSize() {
  201.             return 0;
  202.         }

  204.         /** {@inheritDoc} */
  205.         @Override
  206.         public T getEarliest() {
  207.             throw new OrekitIllegalStateException(OrekitMessages.NO_CACHED_ENTRIES);
  208.         }

  210.         /** {@inheritDoc} */
  211.         @Override
  212.         public T getLatest() {
  213.             throw new OrekitIllegalStateException(OrekitMessages.NO_CACHED_ENTRIES);
  214.         }

  216.         /** {@inheritDoc} */
  217.         @Override
  218.         public List<T> getAll() {
  219.             return Collections.emptyList();
  220.         }

  222.         /** {@inheritDoc} */
  223.         @Override
  224.         public String toString() {
  225.             return "Empty immutable cache";
  226.         }

  228.     }

  230.     /**
  231.      * Get an empty immutable cache, cast to the correct type.
  232.      * @param <TS>  the type of data
  233.      * @return an empty {@link ImmutableTimeStampedCache}.
  234.      */
  235.     @SuppressWarnings("unchecked")
  236.     public static final <TS extends TimeStamped> ImmutableTimeStampedCache<TS> emptyCache() {
  237.         return (ImmutableTimeStampedCache<TS>) EMPTY_CACHE;
  238.     }

  240. }
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