001    /*
002     * Licensed to the Apache Software Foundation (ASF) under one or more
003     * contributor license agreements. See the NOTICE file distributed with
004     * this work for additional information regarding copyright ownership.
005     * The ASF licenses this file to You under the Apache license, Version 2.0
006     * (the "License"); you may not use this file except in compliance with
007     * the License. You may obtain a copy of the License at
008     *
009     *      http://www.apache.org/licenses/LICENSE-2.0
010     *
011     * Unless required by applicable law or agreed to in writing, software
012     * distributed under the License is distributed on an "AS IS" BASIS,
013     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014     * See the license for the specific language governing permissions and
015     * limitations under the license.
016     */
017    package org.apache.logging.log4j.core.util;
018    
019    import java.lang.reflect.Array;
020    
021    /**
022     * A bounded buffer containing elements of type T. When the number of elements to be added will exceed the
023     * size of the buffer the oldest element will be overwritten. Access to the buffer is thread safe.
024     * @param <T> The type of object stored in the buffer.
025     */
026    public final class CyclicBuffer<T> {
027        private final T[] ring;
028        private int first = 0;
029        private int last = 0;
030        private int numElems = 0;
031        private final Class<T> clazz;
032    
033        /**
034         * Instantiate a new CyclicBuffer of at most <code>maxSize</code> events.
035         * @param clazz The Class associate with the type of object in the buffer.
036         * @param size The number of items in the buffer.
037         * @throws IllegalArgumentException if the size is negative.
038         */
039        public CyclicBuffer(final Class<T> clazz, final int size) throws IllegalArgumentException {
040            if (size < 1) {
041                throw new IllegalArgumentException("The maxSize argument (" + size + ") is not a positive integer.");
042            }
043            this.ring = makeArray(clazz, size);
044            this.clazz = clazz;
045        }
046    
047        @SuppressWarnings("unchecked")
048        private T[] makeArray(final Class<T> cls, final int size) {
049            return (T[]) Array.newInstance(cls, size);
050        }
051    
052        /**
053         * Add an item as the last event in the buffer.
054         * @param item The item to add to the buffer.
055         */
056        public synchronized void add(final T item) {
057            ring[last] = item;
058            if (++last == ring.length) {
059                last = 0;
060            }
061    
062            if (numElems < ring.length) {
063                numElems++;
064            } else if (++first == ring.length) {
065                first = 0;
066            }
067        }
068    
069        /**
070         * Removes all the elements from the buffer and returns them.
071         * @return An array of the elements in the buffer.
072         */
073        public synchronized T[] removeAll() {
074            final T[] array = makeArray(clazz, numElems);
075            int index = 0;
076            while (numElems > 0) {
077                numElems--;
078                array[index++] = ring[first];
079                ring[first] = null;
080                if (++first == ring.length) {
081                    first = 0;
082                }
083            }
084            return array;
085        }
086    
087        /**
088         * Determines if the buffer contains elements.
089         * @return true if the buffer is empty, false otherwise.
090         */
091        public boolean isEmpty() {
092            return 0 == numElems;
093        }
094    }