org.apache.log4j.helpers.CyclicBuffer Maven / Gradle / Ivy
/*
* 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;
/**
* Holds {@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.
*
*
* @since 0.9.0
*/
public class CyclicBuffer {
LoggingEvent[] ea;
int first;
int last;
int numElems;
int maxSize;
/**
* Constructs a new instance of at most maxSize events.
*
* The maxSize argument must a positive integer.
*
* @param maxSize The maximum number of elements in the buffer.
*/
public CyclicBuffer(final 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;
}
/**
* Adds an event as the last event in the buffer.
*/
public void add(final LoggingEvent event) {
ea[last] = event;
if (++last == maxSize) {
last = 0;
}
if (numElems < maxSize) {
numElems++;
} else if (++first == maxSize) {
first = 0;
}
}
/**
* Gets 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;
}
/**
* Gets 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(final int i) {
if (i < 0 || i >= numElems) {
return null;
}
return ea[(first + i) % maxSize];
}
public int getMaxSize() {
return maxSize;
}
/**
* Gets 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;
}
/**
* Resizes the cyclic buffer to newSize.
*
* @throws IllegalArgumentException if newSize is negative.
*/
public void resize(final int newSize) {
if (newSize < 0) {
throw new IllegalArgumentException("Negative array size [" + newSize + "] not allowed.");
}
if (newSize == numElems) {
return; // nothing to do
}
final LoggingEvent[] temp = new LoggingEvent[newSize];
final 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;
}
}
}