forked from apache/zookeeper
/
CircularBuffer.java
103 lines (91 loc) · 3.18 KB
/
CircularBuffer.java
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/**
* 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
* <p>
* http://www.apache.org/licenses/LICENSE-2.0
* <p>
* 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.zookeeper.server.util;
import java.lang.reflect.Array;
import java.util.concurrent.atomic.AtomicInteger;
/**
* Thread safe FIFO CircularBuffer implementation.
* When the buffer is full write operation overwrites the oldest element.
*
* Fun thing @todo, make this lock free as this is called on every quorum message
*/
public class CircularBuffer<T> {
private final T[] buffer;
private final int capacity;
private int oldest;
private AtomicInteger numberOfElements = new AtomicInteger();
@SuppressWarnings("unchecked")
public CircularBuffer(Class<T> clazz, int capacity) {
if (capacity <= 0) {
throw new IllegalArgumentException("CircularBuffer capacity should be greater than 0");
}
this.buffer = (T[]) Array.newInstance(clazz, capacity);
this.capacity = capacity;
}
/**
* Puts elements in the next available index in the array.
* If the array is full the oldest element is replaced with
* the new value.
* @param element
*/
public synchronized void write(T element) {
int newSize = numberOfElements.incrementAndGet();
if (newSize > capacity) {
buffer[oldest] = element;
oldest = ++oldest % capacity;
numberOfElements.decrementAndGet();
} else {
int index = (oldest + numberOfElements.get() - 1) % capacity;
buffer[index] = element;
}
}
/**
* Reads from the buffer in a FIFO manner.
* Returns the oldest element in the buffer if the buffer ie not empty
* Returns null if the buffer is empty
* @return
*/
public synchronized T take() {
int newSize = numberOfElements.decrementAndGet();
if (newSize < 0) {
numberOfElements.incrementAndGet();
return null;
}
T polled = buffer[oldest];
oldest = ++oldest % capacity;
return polled;
}
public synchronized T peek() {
if (numberOfElements.get() <= 0) {
return null;
}
return buffer[oldest];
}
public int size() {
return numberOfElements.get();
}
public boolean isEmpty() {
return numberOfElements.get() <= 0;
}
public boolean isFull() {
return numberOfElements.get() >= capacity;
}
public synchronized void reset() {
numberOfElements.set(0);
}
}