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Parallel programming on the go
/*
* Licensed 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 com.gh.bmd.jrt.core;
import java.util.Arrays;
import java.util.Collection;
import java.util.NoSuchElementException;
import javax.annotation.Nonnull;
import javax.annotation.Nullable;
/**
* Minimal implementation of a light-weight queue storing elements into dynamically increasing
* circular buffer.
*
* Created by davide on 9/27/14.
*
* @param the element type.
*/
class SimpleQueue {
private int mFirst;
private int mLast;
private Object[] mQueue = new Object[8];
private static void resizeArray(@Nonnull final T[] src, @Nonnull final T[] dst,
final int first) {
final int remainder = src.length - first;
System.arraycopy(src, 0, dst, 0, first);
System.arraycopy(src, first, dst, dst.length - remainder, remainder);
}
/**
* Adds the specified element to the queue.
*
* Note that the element can be null.
*
* @param element the element to add.
*/
public void add(@Nullable final E element) {
final int i = mLast;
final int newLast = (i + 1) & (mQueue.length - 1);
mQueue[i] = element;
if (mFirst == newLast) {
doubleCapacity();
}
mLast = newLast;
}
/**
* Adds all the elements returned by the specified iterable.
*
* Note that any of the returned element can be null.
*
* @param elements the element iterable.
*/
public void addAll(@Nonnull final Iterable elements) {
for (final E element : elements) {
add(element);
}
}
/**
* Clears the queue.
*/
public void clear() {
mFirst = 0;
mLast = 0;
Arrays.fill(mQueue, null);
}
/**
* Check if the queue does not contain any element.
*
* @return whether the queue is empty.
*/
public boolean isEmpty() {
return mFirst == mLast;
}
/**
* Moves all the elements to the specified collection.
*
* @param collection the collection to fill.
*/
public void moveTo(@Nonnull final Collection collection) {
while (!isEmpty()) {
collection.add(removeFirst());
}
}
/**
* Peeks the first element added into the queue.
*
* @return the element.
* @throws java.util.NoSuchElementException if the queue is empty.
*/
@Nullable
@SuppressWarnings("unchecked")
public E peekFirst() {
if (isEmpty()) {
throw new NoSuchElementException();
}
return (E) mQueue[mFirst];
}
/**
* Removes the first element added into the queue.
*
* @return the element.
* @throws java.util.NoSuchElementException if the queue is empty.
*/
@Nullable
@SuppressWarnings("unchecked")
public E removeFirst() {
if (isEmpty()) {
throw new NoSuchElementException();
}
final Object[] queue = mQueue;
final int i = mFirst;
mFirst = (i + 1) & (queue.length - 1);
final Object output = queue[i];
queue[i] = null;
return (E) output;
}
private void doubleCapacity() {
final int size = mQueue.length;
final int newSize = size << 1;
if (newSize < size) {
throw new OutOfMemoryError();
}
final int first = mFirst;
final int last = mLast;
final Object[] newQueue = new Object[newSize];
resizeArray(mQueue, newQueue, first);
mQueue = newQueue;
final int shift = newSize - size;
mFirst = first + shift;
mLast = (last < first) ? last : last + shift;
}
}