org.eclipse.jgit.storage.dht/src/org/eclipse/jgit/storage/dht/RecentChunks.java

/*
 * Copyright (C) 2011, Google Inc.
 * 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.
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 * - 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.
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 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
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 * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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package org.eclipse.jgit.storage.dht;

import java.io.IOException;

import org.eclipse.jgit.lib.AnyObjectId;
import org.eclipse.jgit.lib.ObjectLoader;
import org.eclipse.jgit.storage.dht.DhtReader.ChunkAndOffset;
import org.eclipse.jgit.storage.dht.RefDataUtil.IdWithChunk;

final class RecentChunks {
	private final DhtReader reader;

	private final DhtReader.Statistics stats;

	private final int maxSize;

	private int curSize;

	private Node lruHead;

	private Node lruTail;

	RecentChunks(DhtReader reader) {
		this.reader = reader;
		this.stats = reader.getStatistics();
		this.maxSize = reader.getOptions().getRecentChunkCacheSize();
	}

	PackChunk get(ChunkKey key) {
		for (Node n = lruHead; n != null; n = n.next) {
			if (key.equals(n.chunk.getChunkKey())) {
				hit(n);
				stats.recentChunks_Hits++;
				return n.chunk;
			}
		}
		stats.recentChunks_Miss++;
		return null;
	}

	void put(PackChunk chunk) {
		for (Node n = lruHead; n != null; n = n.next) {
			if (n.chunk == chunk) {
				hit(n);
				return;
			}
		}

		Node n;
		if (curSize < maxSize) {
			n = new Node();
			curSize++;
		} else {
			n = lruTail;
		}
		n.chunk = chunk;
		hit(n);
	}

	ObjectLoader open(RepositoryKey repo, AnyObjectId objId, int typeHint)
			throws IOException {
		if (objId instanceof IdWithChunk) {
			PackChunk chunk = get(((IdWithChunk) objId).getChunkKey());
			if (chunk != null) {
				int pos = chunk.findOffset(repo, objId);
				if (0 <= pos)
					return PackChunk.read(chunk, pos, reader, typeHint);
			}

			// IdWithChunk is only a hint, and can be wrong. Locally
			// searching is faster than looking in the Database.
		}

		for (Node n = lruHead; n != null; n = n.next) {
			int pos = n.chunk.findOffset(repo, objId);
			if (0 <= pos) {
				hit(n);
				stats.recentChunks_Hits++;
				return PackChunk.read(n.chunk, pos, reader, typeHint);
			}
		}

		return null;
	}

	ChunkAndOffset find(RepositoryKey repo, AnyObjectId objId) {
		if (objId instanceof IdWithChunk) {
			PackChunk chunk = get(((IdWithChunk) objId).getChunkKey());
			if (chunk != null) {
				int pos = chunk.findOffset(repo, objId);
				if (0 <= pos)
					return new ChunkAndOffset(chunk, pos);
			}

			// IdWithChunk is only a hint, and can be wrong. Locally
			// searching is faster than looking in the Database.
		}

		for (Node n = lruHead; n != null; n = n.next) {
			int pos = n.chunk.findOffset(repo, objId);
			if (0 <= pos) {
				hit(n);
				stats.recentChunks_Hits++;
				return new ChunkAndOffset(n.chunk, pos);
			}
		}

		return null;
	}

	boolean has(RepositoryKey repo, AnyObjectId objId) {
		for (Node n = lruHead; n != null; n = n.next) {
			int pos = n.chunk.findOffset(repo, objId);
			if (0 <= pos) {
				hit(n);
				stats.recentChunks_Hits++;
				return true;
			}
		}
		return false;
	}

	void clear() {
		curSize = 0;
		lruHead = null;
		lruTail = null;
	}

	private void hit(Node n) {
		if (lruHead != n) {
			remove(n);
			first(n);
		}
	}

	private void remove(Node node) {
		Node p = node.prev;
		Node n = node.next;

		if (p != null)
			p.next = n;
		if (n != null)
			n.prev = p;

		if (lruHead == node)
			lruHead = n;
		if (lruTail == node)
			lruTail = p;
	}

	private void first(Node node) {
		Node h = lruHead;

		node.prev = null;
		node.next = h;

		if (h != null)
			h.prev = node;
		else
			lruTail = node;

		lruHead = node;
	}

	private static class Node {
		PackChunk chunk;

		Node prev;

		Node next;
	}
}