| /* |
| * Copyright (C) 2010, Google Inc. and others |
| * |
| * This program and the accompanying materials are made available under the |
| * terms of the Eclipse Distribution License v. 1.0 which is available at |
| * https://www.eclipse.org/org/documents/edl-v10.php. |
| * |
| * SPDX-License-Identifier: BSD-3-Clause |
| */ |
| |
| package org.eclipse.jgit.internal.storage.file; |
| |
| import java.util.concurrent.atomic.AtomicReferenceArray; |
| |
| import org.eclipse.jgit.lib.AnyObjectId; |
| import org.eclipse.jgit.lib.ObjectId; |
| |
| /** Remembers objects that are currently unpacked. */ |
| class UnpackedObjectCache { |
| private static final int INITIAL_BITS = 5; // size = 32 |
| |
| private static final int MAX_BITS = 11; // size = 2048 |
| |
| private volatile Table table; |
| |
| UnpackedObjectCache() { |
| table = new Table(INITIAL_BITS); |
| } |
| |
| boolean isUnpacked(AnyObjectId objectId) { |
| return table.contains(objectId); |
| } |
| |
| void add(AnyObjectId objectId) { |
| Table t = table; |
| if (t.add(objectId)) { |
| // The object either already exists in the table, or was |
| // successfully added. Either way leave the table alone. |
| // |
| } else { |
| // The object won't fit into the table. Implement a crude |
| // cache removal by just dropping the table away, but double |
| // it in size for the next incarnation. |
| // |
| Table n = new Table(Math.min(t.bits + 1, MAX_BITS)); |
| n.add(objectId); |
| table = n; |
| } |
| } |
| |
| void remove(AnyObjectId objectId) { |
| if (isUnpacked(objectId)) |
| clear(); |
| } |
| |
| void clear() { |
| table = new Table(INITIAL_BITS); |
| } |
| |
| private static class Table { |
| private static final int MAX_CHAIN = 8; |
| |
| private final AtomicReferenceArray<ObjectId> ids; |
| |
| private final int shift; |
| |
| final int bits; |
| |
| Table(int bits) { |
| this.ids = new AtomicReferenceArray<>(1 << bits); |
| this.shift = 32 - bits; |
| this.bits = bits; |
| } |
| |
| boolean contains(AnyObjectId toFind) { |
| int i = index(toFind); |
| for (int n = 0; n < MAX_CHAIN; n++) { |
| ObjectId obj = ids.get(i); |
| if (obj == null) |
| break; |
| |
| if (AnyObjectId.isEqual(obj, toFind)) |
| return true; |
| |
| if (++i == ids.length()) |
| i = 0; |
| } |
| return false; |
| } |
| |
| boolean add(AnyObjectId toAdd) { |
| int i = index(toAdd); |
| for (int n = 0; n < MAX_CHAIN;) { |
| ObjectId obj = ids.get(i); |
| if (obj == null) { |
| if (ids.compareAndSet(i, null, toAdd.copy())) { |
| return true; |
| } |
| continue; |
| } |
| |
| if (AnyObjectId.isEqual(obj, toAdd)) { |
| return true; |
| } |
| |
| if (++i == ids.length()) { |
| i = 0; |
| } |
| n++; |
| } |
| return false; |
| } |
| |
| private int index(AnyObjectId id) { |
| return id.hashCode() >>> shift; |
| } |
| } |
| } |