1 /*
2 * Licensed to the Apache Software Foundation (ASF) under one or more
3 * contributor license agreements. See the NOTICE file distributed with
4 * this work for additional information regarding copyright ownership.
5 * The ASF 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.apache.logging.log4j.core.util;
18
19 import java.lang.reflect.Array;
20
21 /**
22 * A bounded buffer containing elements of type T. When the number of elements to be added will exceed the
23 * size of the buffer the oldest element will be overwritten. Access to the buffer is thread safe.
24 * @param <T> The type of object stored in the buffer.
25 */
26 public final class CyclicBuffer<T> {
27 private final T[] ring;
28 private int first = 0;
29 private int last = 0;
30 private int numElems = 0;
31 private final Class<T> clazz;
32
33 /**
34 * Instantiates a new CyclicBuffer of at most <code>maxSize</code> events.
35 * @param clazz The Class associate with the type of object in the buffer.
36 * @param size The number of items in the buffer.
37 * @throws IllegalArgumentException if the size is negative.
38 */
39 public CyclicBuffer(final Class<T> clazz, final int size) throws IllegalArgumentException {
40 if (size < 0) {
41 throw new IllegalArgumentException("The maxSize argument (" + size + ") cannot be negative.");
42 }
43 this.ring = makeArray(clazz, size);
44 this.clazz = clazz;
45 }
46
47 @SuppressWarnings("unchecked")
48 private T[] makeArray(final Class<T> cls, final int size) {
49 return (T[]) Array.newInstance(cls, size);
50 }
51
52 /**
53 * Adds an item as the last event in the buffer.
54 * @param item The item to add to the buffer.
55 */
56 public synchronized void add(final T item) {
57 if (ring.length > 0) {
58 ring[last] = item;
59 if (++last == ring.length) {
60 last = 0;
61 }
62
63 if (numElems < ring.length) {
64 numElems++;
65 } else if (++first == ring.length) {
66 first = 0;
67 }
68 }
69 }
70
71 /**
72 * Removes all the elements from the buffer and returns them.
73 * @return An array of the elements in the buffer.
74 */
75 public synchronized T[] removeAll() {
76 final T[] array = makeArray(clazz, numElems);
77 int index = 0;
78 while (numElems > 0) {
79 numElems--;
80 array[index++] = ring[first];
81 ring[first] = null;
82 if (++first == ring.length) {
83 first = 0;
84 }
85 }
86 return array;
87 }
88
89 /**
90 * Determines if the buffer contains elements.
91 * @return true if the buffer is empty, false otherwise.
92 */
93 public boolean isEmpty() {
94 return 0 == numElems;
95 }
96 }