+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.log4j.helpers;
+
+import org.apache.log4j.spi.LoggingEvent;
+
+/**
+
+ CyclicBuffer is used by other appenders to hold {@link LoggingEvent
+ LoggingEvents} for immediate or differed display.
+
+ <p>This buffer gives read access to any element in the buffer not
+ just the first or last element.
+
+ @author Ceki Gülcü
+ @since 0.9.0
+
+ */
+public class CyclicBuffer {
+
+ LoggingEvent[] ea;
+ int first;
+ int last;
+ int numElems;
+ int maxSize;
+
+ /**
+ Instantiate a new CyclicBuffer of at most <code>maxSize</code> events.
+
+ The <code>maxSize</code> argument must a positive integer.
+
+ @param maxSize The maximum number of elements in the buffer.
+ */
+ public CyclicBuffer(int maxSize) throws IllegalArgumentException {
+ if(maxSize < 1) {
+ throw new IllegalArgumentException("The maxSize argument ("+maxSize+
+ ") is not a positive integer.");
+ }
+ this.maxSize = maxSize;
+ ea = new LoggingEvent[maxSize];
+ first = 0;
+ last = 0;
+ numElems = 0;
+ }
+
+ /**
+ Add an <code>event</code> as the last event in the buffer.
+
+ */
+ public
+ void add(LoggingEvent event) {
+ ea[last] = event;
+ if(++last == maxSize) {
+ last = 0;
+ }
+
+ if(numElems < maxSize) {
+ numElems++;
+ } else if(++first == maxSize) {
+ first = 0;
+ }
+ }
+
+
+ /**
+ Get the <i>i</i>th oldest event currently in the buffer. If
+ <em>i</em> is outside the range 0 to the number of elements
+ currently in the buffer, then <code>null</code> is returned.
+
+
+ */
+ public
+ LoggingEvent get(int i) {
+ if(i < 0 || i >= numElems) {
+ return null;
+ }
+
+ return ea[(first + i) % maxSize];
+ }
+
+ public
+ int getMaxSize() {
+ return maxSize;
+ }
+
+ /**
+ Get the oldest (first) element in the buffer. The oldest element
+ is removed from the buffer.
+ */
+ public
+ LoggingEvent get() {
+ LoggingEvent r = null;
+ if(numElems > 0) {
+ numElems--;
+ r = ea[first];
+ ea[first] = null;
+ if(++first == maxSize) {
+ first = 0;
+ }
+ }
+ return r;
+ }
+
+ /**
+ Get the number of elements in the buffer. This number is
+ guaranteed to be in the range 0 to <code>maxSize</code>
+ (inclusive).
+ */
+ public
+ int length() {
+ return numElems;
+ }
+
+ /**
+ Resize the cyclic buffer to <code>newSize</code>.
+
+ @throws IllegalArgumentException if <code>newSize</code> is negative.
+ */
+ public
+ void resize(int newSize) {
+ if(newSize < 0) {
+ throw new IllegalArgumentException("Negative array size ["+newSize+
+ "] not allowed.");
+ }
+ if(newSize == numElems)
+ {
+ return; // nothing to do
+ }
+
+ LoggingEvent[] temp = new LoggingEvent[newSize];
+
+ int loopLen = newSize < numElems ? newSize : numElems;
+
+ for(int i = 0; i < loopLen; i++) {
+ temp[i] = ea[first];
+ ea[first] = null;
+ if(++first == numElems) {
+ first = 0;
+ }
+ }
+ ea = temp;
+ first = 0;
+ numElems = loopLen;
+ maxSize = newSize;
+ if (loopLen == newSize) {
+ last = 0;
+ } else {
+ last = loopLen;
+ }
+ }
+}