/* * 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.

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 maxSize events. The maxSize 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 event 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 ith oldest event currently in the buffer. If i is outside the range 0 to the number of elements currently in the buffer, then null 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 maxSize (inclusive). */ public int length() { return numElems; } /** Resize the cyclic buffer to newSize. @throws IllegalArgumentException if newSize 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; } } }