/*
* Copyright (C) The Apache Software Foundation. All rights reserved.
*
* This software is published under the terms of the Apache Software License
* version 1.1, a copy of which has been included with this distribution in
* the LICENSE.txt file.
*/
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;
}
}
}
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