Java tutorial
/** * * Licensed to the Apache Software Foundation (ASF) under one * or more contributor license agreements. See the NOTICE file * distributed with this work for additional information * regarding copyright ownership. The ASF licenses this file * to you 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 org.apache.bookkeeper.bookie.storage.ldb; import static org.apache.bookkeeper.bookie.storage.ldb.WriteCache.align64; import io.netty.buffer.ByteBuf; import io.netty.buffer.ByteBufAllocator; import io.netty.buffer.Unpooled; import java.io.Closeable; import java.util.ArrayList; import java.util.List; import java.util.concurrent.atomic.AtomicInteger; import java.util.concurrent.locks.ReentrantReadWriteLock; import org.apache.bookkeeper.util.collections.ConcurrentLongLongPairHashMap; import org.apache.bookkeeper.util.collections.ConcurrentLongLongPairHashMap.LongPair; /** * Read cache implementation. * * <p>Uses the specified amount of memory and pairs it with a hashmap. * * <p>The memory is splitted in multiple segments that are used in a * ring-buffer fashion. When the read cache is full, the oldest segment * is cleared and rotated to make space for new entries to be added to * the read cache. */ public class ReadCache implements Closeable { private static final int DEFAULT_MAX_SEGMENT_SIZE = 1 * 1024 * 1024 * 1024; private final List<ByteBuf> cacheSegments; private final List<ConcurrentLongLongPairHashMap> cacheIndexes; private int currentSegmentIdx; private final AtomicInteger currentSegmentOffset = new AtomicInteger(0); private final int segmentSize; private ByteBufAllocator allocator; private final ReentrantReadWriteLock lock = new ReentrantReadWriteLock(); public ReadCache(ByteBufAllocator allocator, long maxCacheSize) { this(allocator, maxCacheSize, DEFAULT_MAX_SEGMENT_SIZE); } public ReadCache(ByteBufAllocator allocator, long maxCacheSize, int maxSegmentSize) { this.allocator = allocator; int segmentsCount = Math.max(2, (int) (maxCacheSize / maxSegmentSize)); segmentSize = (int) (maxCacheSize / segmentsCount); cacheSegments = new ArrayList<>(); cacheIndexes = new ArrayList<>(); for (int i = 0; i < segmentsCount; i++) { cacheSegments.add(Unpooled.directBuffer(segmentSize, segmentSize)); cacheIndexes .add(new ConcurrentLongLongPairHashMap(4096, 2 * Runtime.getRuntime().availableProcessors())); } } @Override public void close() { cacheSegments.forEach(ByteBuf::release); } public void put(long ledgerId, long entryId, ByteBuf entry) { int entrySize = entry.readableBytes(); int alignedSize = align64(entrySize); lock.readLock().lock(); try { int offset = currentSegmentOffset.getAndAdd(alignedSize); if (offset + entrySize > segmentSize) { // Roll-over the segment (outside the read-lock) } else { // Copy entry into read cache segment cacheSegments.get(currentSegmentIdx).setBytes(offset, entry, entry.readerIndex(), entry.readableBytes()); cacheIndexes.get(currentSegmentIdx).put(ledgerId, entryId, offset, entrySize); return; } } finally { lock.readLock().unlock(); } // We could not insert in segment, we to get the write lock and roll-over to // next segment lock.writeLock().lock(); try { int offset = currentSegmentOffset.getAndAdd(entrySize); if (offset + entrySize > segmentSize) { // Rollover to next segment currentSegmentIdx = (currentSegmentIdx + 1) % cacheSegments.size(); currentSegmentOffset.set(alignedSize); cacheIndexes.get(currentSegmentIdx).clear(); offset = 0; } // Copy entry into read cache segment cacheSegments.get(currentSegmentIdx).setBytes(offset, entry, entry.readerIndex(), entry.readableBytes()); cacheIndexes.get(currentSegmentIdx).put(ledgerId, entryId, offset, entrySize); } finally { lock.writeLock().unlock(); } } public ByteBuf get(long ledgerId, long entryId) { lock.readLock().lock(); try { // We need to check all the segments, starting from the current one and looking // backward to minimize the // checks for recently inserted entries int size = cacheSegments.size(); for (int i = 0; i < size; i++) { int segmentIdx = (currentSegmentIdx + (size - i)) % size; LongPair res = cacheIndexes.get(segmentIdx).get(ledgerId, entryId); if (res != null) { int entryOffset = (int) res.first; int entryLen = (int) res.second; ByteBuf entry = allocator.directBuffer(entryLen, entryLen); entry.writeBytes(cacheSegments.get(segmentIdx), entryOffset, entryLen); return entry; } } } finally { lock.readLock().unlock(); } // Entry not found in any segment return null; } /** * @return the total size of cached entries */ public long size() { lock.readLock().lock(); try { long size = 0; for (int i = 0; i < cacheIndexes.size(); i++) { if (i == currentSegmentIdx) { size += currentSegmentOffset.get(); } else if (!cacheIndexes.get(i).isEmpty()) { size += segmentSize; } else { // the segment is empty } } return size; } finally { lock.readLock().unlock(); } } /** * @return the total number of cached entries */ public long count() { lock.readLock().lock(); try { long count = 0; for (int i = 0; i < cacheIndexes.size(); i++) { count += cacheIndexes.get(i).size(); } return count; } finally { lock.readLock().unlock(); } } }