content: /*
   *
   * 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 io.netty.util.ReferenceCountUtil;
  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;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  /**
   * Read cache implementation.
   *
   * <p>Uses the specified amount of memory and pairs it with a hashmap.
   *
   * <p>The memory is split 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 Logger log = LoggerFactory.getLogger(ReadCache.class);
  
      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));
              ConcurrentLongLongPairHashMap concurrentLongLongPairHashMap = ConcurrentLongLongPairHashMap.newBuilder()
                      .expectedItems(4096)
                      .concurrencyLevel(2 * Runtime.getRuntime().availableProcessors())
                      .build();
              cacheIndexes.add(concurrentLongLongPairHashMap);
          }
      }
  
      @Override
      public void close() {
          cacheSegments.forEach(ReferenceCountUtil::safeRelease);
      }
  
      public void put(long ledgerId, long entryId, ByteBuf entry) {
          int entrySize = entry.readableBytes();
          int alignedSize = align64(entrySize);
  
          lock.readLock().lock();
  
          try {
              if (entrySize > segmentSize) {
                  log.warn("entrySize {} > segmentSize {}, skip update read cache!", entrySize, segmentSize);
                  return;
              }
              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.buffer(entryLen, entryLen);
                      entry.writeBytes(cacheSegments.get(segmentIdx), entryOffset, entryLen);
                      return entry;
                  }
              }
          } finally {
              lock.readLock().unlock();
          }
  
          // Entry not found in any segment
          return null;
      }
  
      public boolean hasEntry(long ledgerId, long entryId) {
          lock.readLock().lock();
  
          try {
              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) {
                      return true;
                  }
              }
          } finally {
              lock.readLock().unlock();
          }
  
          // Entry not found in any segment
          return false;
      }
  
      /**
       * @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();
          }
      }
  }
  