1 package org.jscsi.target.util;
2
3 /**
4 * Instances of this class can serve as a source for byte arrays of specified lengths. Up to {@link #capacity} arrays of
5 * different lengths can be stored, quickly retrievable with the {@link #getArray(int)} method. Frequently requested
6 * arrays will be returned faster, less frequently used arrays might have to be initialized first and are more likely to
7 * be removed.
8 *
9 * @author Andreas Ergenzinger
10 */
11 public final class FastByteArrayProvider {
12
13 /**
14 * Contains the stored byte arrays.
15 */
16 final byte[][] arrays;
17
18 /**
19 * The maximum number of array that can be stored.
20 */
21 final int capacity;
22
23 /**
24 * The total number of stored arrays.
25 */
26 int size = 0;
27
28 /**
29 * A temporary byte array reference used by {@link #getArray(int)};
30 */
31 byte[] tmp;
32
33 /**
34 * The constructor.
35 *
36 * @param capacity the {@link #capacity} of the created object.
37 */
38 public FastByteArrayProvider (final int capacity) {
39 this.capacity = capacity;
40 arrays = new byte[capacity][];
41 }
42
43 /**
44 * Returns a byte array of the specified length.
45 * <p>
46 * Note that the returned array may have been used before and therefore the array's values are not guaranteed to be
47 * <code>0</code>.
48 * <p>
49 * The method consecutively checks {@link #arrays} for an array of the correct length. If such an array exists, it
50 * will be moved to one index position closer to the front of the array (if possible), speeding up future retrievals
51 * of the same array.
52 *
53 * @param length the length of the returned array
54 * @return a byte array of the specified length
55 */
56 public byte[] getArray (final int length) {
57 for (int i = 0; i < size; ++i) {
58 if (length == arrays[i].length) {
59 // swap (if not already at the front) and return
60 if (i > 0) {
61 tmp = arrays[i];
62 arrays[i] = arrays[i - 1];
63 arrays[i - 1] = tmp;
64 return tmp;
65 }
66 // no swapping, so element was and still is at the front of the
67 // list
68 return arrays[0];
69 }
70 }
71 // requested array does not exist, add to tail of queue,
72 tmp = new byte[length];
73 if (size == capacity) --size;// replace last element
74 arrays[size] = tmp;
75 ++size;
76 return tmp;
77 }
78
79 /**
80 * Returns all stored byte arrays.
81 * <p>
82 * This method's primary purpose is to enable testing of byte array storing and reordering.
83 *
84 * @return {@link #arrays}.
85 */
86 public byte[][] getAll () {
87 return arrays;
88 }
89 }