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/*
* Copyright (C) 2011, 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.dfs;
/**
* Caches recently used objects for {@link DfsReader}.
* <p>
* This cache is not thread-safe. Each reader should have its own cache.
*/
final class DeltaBaseCache {
private static final int TABLE_BITS = 10;
private static final int MASK_BITS = 32 - TABLE_BITS;
private static int hash(long position) {
return (((int) position) << MASK_BITS) >>> MASK_BITS;
}
private int maxByteCount;
private int curByteCount;
private final Entry[] table;
private Entry lruHead;
private Entry lruTail;
DeltaBaseCache(DfsReader reader) {
this(reader.getOptions().getDeltaBaseCacheLimit());
}
DeltaBaseCache(int maxBytes) {
maxByteCount = maxBytes;
table = new Entry[1 << TABLE_BITS];
}
Entry get(DfsStreamKey key, long position) {
Entry e = table[hash(position)];
for (; e != null; e = e.tableNext) {
if (e.offset == position && key.equals(e.pack)) {
moveToHead(e);
return e;
}
}
return null;
}
void put(DfsStreamKey key, long offset, int objectType, byte[] data) {
if (data.length > maxByteCount)
return; // Too large to cache.
curByteCount += data.length;
releaseMemory();
int tableIdx = hash(offset);
Entry e = new Entry(key, offset, objectType, data);
e.tableNext = table[tableIdx];
table[tableIdx] = e;
lruPushHead(e);
}
private void releaseMemory() {
while (curByteCount > maxByteCount && lruTail != null) {
Entry e = lruTail;
curByteCount -= e.data.length;
lruRemove(e);
removeFromTable(e);
}
}
private void removeFromTable(Entry e) {
int tableIdx = hash(e.offset);
Entry p = table[tableIdx];
if (p == e) {
table[tableIdx] = e.tableNext;
return;
}
for (; p != null; p = p.tableNext) {
if (p.tableNext == e) {
p.tableNext = e.tableNext;
return;
}
}
throw new IllegalStateException(String.format(
"entry for %s:%d not in table", //$NON-NLS-1$
e.pack, Long.valueOf(e.offset)));
}
private void moveToHead(Entry e) {
if (e != lruHead) {
lruRemove(e);
lruPushHead(e);
}
}
private void lruRemove(Entry e) {
Entry p = e.lruPrev;
Entry n = e.lruNext;
if (p != null) {
p.lruNext = n;
} else {
lruHead = n;
}
if (n != null) {
n.lruPrev = p;
} else {
lruTail = p;
}
}
private void lruPushHead(Entry e) {
Entry n = lruHead;
e.lruNext = n;
if (n != null)
n.lruPrev = e;
else
lruTail = e;
e.lruPrev = null;
lruHead = e;
}
int getMemoryUsed() {
return curByteCount;
}
int getMemoryUsedByLruChainForTest() {
int r = 0;
for (Entry e = lruHead; e != null; e = e.lruNext) {
r += e.data.length;
}
return r;
}
int getMemoryUsedByTableForTest() {
int r = 0;
for (Entry t : table) {
for (Entry e = t; e != null; e = e.tableNext) {
r += e.data.length;
}
}
return r;
}
static class Entry {
final DfsStreamKey pack;
final long offset;
final int type;
final byte[] data;
Entry tableNext;
Entry lruPrev;
Entry lruNext;
Entry(DfsStreamKey key, long offset, int type, byte[] data) {
this.pack = key;
this.offset = offset;
this.type = type;
this.data = data;
}
}
}
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