org.apache.log4j.helpers.BoundedFIFO 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;
/**
* Bounded first-in-first-out buffer.
*
* @since version 0.9.1
*/
public class BoundedFIFO {
LoggingEvent[] buf;
int numElements = 0;
int first = 0;
int next = 0;
int maxSize;
/**
* Constructs a new instance with a maximum size passed as argument.
*/
public BoundedFIFO(final int maxSize) {
if (maxSize < 1) {
throw new IllegalArgumentException("The maxSize argument (" + maxSize + ") is not a positive integer.");
}
this.maxSize = maxSize;
buf = new LoggingEvent[maxSize];
}
/**
* Gets the first element in the buffer. Returns null if there are no elements in the buffer.
*/
public LoggingEvent get() {
if (numElements == 0) {
return null;
}
final LoggingEvent r = buf[first];
buf[first] = null; // help garbage collection
if (++first == maxSize) {
first = 0;
}
numElements--;
return r;
}
/**
* Gets the maximum size of the buffer.
*/
public int getMaxSize() {
return maxSize;
}
/**
* Returns true if the buffer is full, that is, whether the number of elements in the buffer equals the
* buffer size.
*/
public boolean isFull() {
return numElements == 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 numElements;
}
int min(final int a, final int b) {
return a < b ? a : b;
}
/**
* Puts a {@link LoggingEvent} in the buffer. If the buffer is full then the event is silently dropped. It is the
* caller's responsability to make sure that the buffer has free space.
*/
public void put(final LoggingEvent o) {
if (numElements != maxSize) {
buf[next] = o;
if (++next == maxSize) {
next = 0;
}
numElements++;
}
}
/**
* Resizes the buffer to a new size. If the new size is smaller than the old size events might be lost.
*
* @since 1.1
*/
synchronized public void resize(final int newSize) {
if (newSize == maxSize) {
return;
}
final LoggingEvent[] tmp = new LoggingEvent[newSize];
// we should not copy beyond the buf array
int len1 = maxSize - first;
// we should not copy beyond the tmp array
len1 = min(len1, newSize);
// er.. how much do we actually need to copy?
// We should not copy more than the actual number of elements.
len1 = min(len1, numElements);
// Copy from buf starting a first, to tmp, starting at position 0, len1 elements.
System.arraycopy(buf, first, tmp, 0, len1);
// Are there any uncopied elements and is there still space in the new array?
int len2 = 0;
if ((len1 < numElements) && (len1 < newSize)) {
len2 = numElements - len1;
len2 = min(len2, newSize - len1);
System.arraycopy(buf, 0, tmp, len1, len2);
}
this.buf = tmp;
this.maxSize = newSize;
this.first = 0;
this.numElements = len1 + len2;
this.next = this.numElements;
if (this.next == this.maxSize) {
this.next = 0;
}
}
/**
* Returns true if there is just one element in the buffer. In other words, if there were no elements
* before the last {@link #put} operation completed.
*/
public boolean wasEmpty() {
return numElements == 1;
}
/**
* Returns true if the number of elements in the buffer plus 1 equals the maximum buffer size, returns
* false otherwise.
*/
public boolean wasFull() {
return numElements + 1 == maxSize;
}
}