/*
 * Copyright (C) 2008, Shawn O. Pearce <spearce@spearce.org>
 * and other copyright owners as documented in the project's IP log.
 *
 * This program and the accompanying materials are made available
 * under the terms of the Eclipse Distribution License v1.0 which
 * accompanies this distribution, is reproduced below, and is
 * available at http://www.eclipse.org/org/documents/edl-v10.php
 *
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or
 * without modification, are permitted provided that the following
 * conditions are met:
 *
 * - Redistributions of source code must retain the above copyright
 *   notice, this list of conditions and the following disclaimer.
 *
 * - Redistributions in binary form must reproduce the above
 *   copyright notice, this list of conditions and the following
 *   disclaimer in the documentation and/or other materials provided
 *   with the distribution.
 *
 * - Neither the name of the Eclipse Foundation, Inc. nor the
 *   names of its contributors may be used to endorse or promote
 *   products derived from this software without specific prior
 *   written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
 * CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
 * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
 * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
 * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

package org.eclipse.jgit.revwalk;

import java.io.IOException;

import org.eclipse.jgit.errors.IncorrectObjectTypeException;
import org.eclipse.jgit.errors.MissingObjectException;

abstract class BlockRevQueue extends AbstractRevQueue {
	protected BlockFreeList free;

	
Create an empty revision queue.
Params:
firstParent – 
           whether only first-parent links should be followed when
           walking/**
	 * Create an empty revision queue.
	 *
	 * @param firstParent
	 *            whether only first-parent links should be followed when
	 *            walking
	 */
	protected BlockRevQueue(boolean firstParent) {
		super(firstParent);
		free = new BlockFreeList();
	}

	BlockRevQueue(Generator s) throws MissingObjectException,
			IncorrectObjectTypeException, IOException {
		super(s.firstParent);
		free = new BlockFreeList();
		outputType = s.outputType();
		s.shareFreeList(this);
		for (;;) {
			final RevCommit c = s.next();
			if (c == null)
				break;
			add(c);
		}
	}

	
{@inheritDoc}

Reconfigure this queue to share the same free list as another.

Multiple revision queues can be connected to the same free list, making
it less expensive for applications to shuttle commits between them. This
method arranges for the receiver to take from / return to the same free
list as the supplied queue.

Free lists are not thread-safe. Applications must ensure that all queues
sharing the same free list are doing so from only a single thread.
/**
	 * {@inheritDoc}
	 * <p>
	 * Reconfigure this queue to share the same free list as another.
	 * <p>
	 * Multiple revision queues can be connected to the same free list, making
	 * it less expensive for applications to shuttle commits between them. This
	 * method arranges for the receiver to take from / return to the same free
	 * list as the supplied queue.
	 * <p>
	 * Free lists are not thread-safe. Applications must ensure that all queues
	 * sharing the same free list are doing so from only a single thread.
	 */
	@Override
	public void shareFreeList(BlockRevQueue q) {
		free = q.free;
	}

	static final class BlockFreeList {
		private Block next;

		Block newBlock() {
			Block b = next;
			if (b == null)
				return new Block();
			next = b.next;
			b.clear();
			return b;
		}

		void freeBlock(Block b) {
			b.next = next;
			next = b;
		}

		void clear() {
			next = null;
		}
	}

	static final class Block {
		static final int BLOCK_SIZE = 256;

		
Next block in our chain of blocks; null if we are the last. /** Next block in our chain of blocks; null if we are the last. */
		Block next;

		
Our table of queued commits. /** Our table of queued commits. */
		final RevCommit[] commits = new RevCommit[BLOCK_SIZE];

		
Next valid entry in commits. /** Next valid entry in {@link #commits}. */
		int headIndex;

		
Next free entry in commits for addition at. /** Next free entry in {@link #commits} for addition at. */
		int tailIndex;

		boolean isFull() {
			return tailIndex == BLOCK_SIZE;
		}

		boolean isEmpty() {
			return headIndex == tailIndex;
		}

		boolean canUnpop() {
			return headIndex > 0;
		}

		void add(RevCommit c) {
			commits[tailIndex++] = c;
		}

		void unpop(RevCommit c) {
			commits[--headIndex] = c;
		}

		RevCommit pop() {
			return commits[headIndex++];
		}

		RevCommit peek() {
			return commits[headIndex];
		}

		void clear() {
			next = null;
			headIndex = 0;
			tailIndex = 0;
		}

		void resetToMiddle() {
			headIndex = tailIndex = BLOCK_SIZE / 2;
		}

		void resetToEnd() {
			headIndex = tailIndex = BLOCK_SIZE;
		}
	}
}