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;
  
  import java.io.File;
  import java.io.IOException;
  import java.io.UncheckedIOException;
  import java.util.concurrent.atomic.AtomicInteger;
  import java.util.concurrent.locks.ReentrantReadWriteLock;
  import lombok.extern.slf4j.Slf4j;
  import org.apache.bookkeeper.util.collections.ConcurrentLongHashMap;
  
  @Slf4j
  class FileInfoBackingCache {
      static final int DEAD_REF = -0xdead;
  
      final ReentrantReadWriteLock lock = new ReentrantReadWriteLock();
      final ConcurrentLongHashMap<CachedFileInfo> fileInfos =
              ConcurrentLongHashMap.<CachedFileInfo>newBuilder().build();
      final FileLoader fileLoader;
      final int fileInfoVersionToWrite;
  
      FileInfoBackingCache(FileLoader fileLoader, int fileInfoVersionToWrite) {
          this.fileLoader = fileLoader;
          this.fileInfoVersionToWrite = fileInfoVersionToWrite;
      }
  
      /**
       * This method should be under `lock` of FileInfoBackingCache.
       */
      private static CachedFileInfo tryRetainFileInfo(CachedFileInfo fi) throws IOException {
          boolean retained = fi.tryRetain();
          if (!retained) {
              throw new IOException("FileInfo " + fi + " is already marked dead");
          } else if (fi.isDeleted()) {
              throw new Bookie.NoLedgerException(fi.ledgerId);
          }
          return fi;
      }
  
      CachedFileInfo loadFileInfo(long ledgerId, byte[] masterKey) throws IOException {
          lock.readLock().lock();
          try {
              CachedFileInfo fi = fileInfos.get(ledgerId);
              if (fi != null) {
                  // tryRetain only fails if #markDead() has been called
                  // on fi. This is only called from within the write lock,
                  // and if it is called (and succeeds) the fi will have been
                  // removed from fileInfos at the same time, so we should not
                  // have been able to get a reference to it here.
                  // The caller of loadFileInfo owns the reference, and is
                  // responsible for calling the corresponding #release().
                  return tryRetainFileInfo(fi);
              }
          } finally {
              lock.readLock().unlock();
          }
  
          File backingFile = fileLoader.load(ledgerId, masterKey != null);
          CachedFileInfo newFi = new CachedFileInfo(ledgerId, backingFile, masterKey);
  
          // else FileInfo not found, create it under write lock
          lock.writeLock().lock();
          try {
              CachedFileInfo fi = fileInfos.get(ledgerId);
              if (fi != null) {
                  // someone is already putting a fileinfo here, so use the existing one and recycle the new one
                  newFi.recycle();
              } else {
                  fileInfos.put(ledgerId, newFi);
                  fi = newFi;
              }
  
              // see comment above for why we assert
              return tryRetainFileInfo(fi);
          } finally {
              lock.writeLock().unlock();
          }
      }
  
      private void releaseFileInfo(long ledgerId, CachedFileInfo fileInfo) {
          lock.writeLock().lock();
          try {
              if (fileInfo.markDead()) {
                  fileInfo.close(true);
                  fileInfos.remove(ledgerId, fileInfo);
              }
          } catch (IOException ioe) {
              log.error("Error evicting file info({}) for ledger {} from backing cache",
                        fileInfo, ledgerId, ioe);
          } finally {
              lock.writeLock().unlock();
          }
      }
  
      void closeAllWithoutFlushing() throws IOException {
          try {
              fileInfos.forEach((key, fileInfo) -> {
                  try {
                      fileInfo.close(false);
                  } catch (IOException e) {
                      throw new UncheckedIOException(e);
                  }
              });
          } catch (UncheckedIOException uioe) {
              throw uioe.getCause();
          }
      }
  
      class CachedFileInfo extends FileInfo {
          final long ledgerId;
          final AtomicInteger refCount;
  
          CachedFileInfo(long ledgerId, File lf, byte[] masterKey) throws IOException {
              super(lf, masterKey, fileInfoVersionToWrite);
              this.ledgerId = ledgerId;
              this.refCount = new AtomicInteger(0);
          }
  
          /**
           * Mark this fileinfo as dead. We can only mark a fileinfo as
           * dead if noone currently holds a reference to it.
           *
           * @return true if we marked as dead, false otherwise
           */
          private boolean markDead() {
              return refCount.compareAndSet(0, DEAD_REF);
          }
  
          /**
           * Attempt to retain the file info.
           * When a client obtains a fileinfo from a container object,
           * but that container object may release the fileinfo before
           * the client has a chance to call retain. In this case, the
           * file info could be released and the destroyed before we ever
           * get a chance to use it.
           *
           * <p>tryRetain avoids this problem, by doing a compare-and-swap on
           * the reference count. If the refCount is negative, it means that
           * the fileinfo is being cleaned up, and this fileinfo object should
           * not be used. This works in tandem with #markDead, which will only
           * set the refCount to negative if noone currently has it retained
           * (i.e. the refCount is 0).
           *
           * @return true if we managed to increment the refcount, false otherwise
           */
          boolean tryRetain() {
              while (true) {
                  int count = refCount.get();
                  if (count < 0) {
                      return false;
                  } else if (refCount.compareAndSet(count, count + 1)) {
                      return true;
                  }
              }
          }
  
          int getRefCount() {
              return refCount.get();
          }
  
          void release() {
              if (refCount.decrementAndGet() == 0) {
                  releaseFileInfo(ledgerId, this);
              }
          }
  
          @Override
          public String toString() {
              return "CachedFileInfo(ledger=" + ledgerId
                  + ",refCount=" + refCount.get()
                  + ",closed=" + isClosed()
                  + ",id=" + System.identityHashCode(this) + ")";
          }
      }
  
      interface FileLoader {
          File load(long ledgerId, boolean createIfMissing) throws IOException;
      }
  }
  