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.cassandra.io;
  
  import java.nio.channels.FileChannel;
  import java.nio.file.OpenOption;
  import java.nio.file.Path;
  import java.nio.file.attribute.FileAttribute;
  import java.util.Collections;
  import java.util.HashMap;
  import java.util.IdentityHashMap;
  import java.util.Map;
  import java.util.Set;
  import java.util.stream.Collectors;
  import javax.annotation.Nullable;
  
  import org.apache.cassandra.io.filesystem.ListenableFileSystem;
  
  /**
   * Listeners to aid in debugging and monitoring of disk issues.  The class is normally unused as its target is to help
   * debug issues, for this reason its likely dead code most of the time... it's here when you need it!
   */
  @SuppressWarnings("unused")
  public class FileSystemListeners
  {
      /**
       * Adds a listener to {@link ListenableFileSystem} that will track open/close/delete operations.  If a path delete
       * is detected before the file is closed, this will throw an exception as this could be due to a possible filesystem leak.
       * A filesystem leak can be very dangerous as the allocated disk space keeps growing and growing, but when you look
       * at the file system you won't see all the space as taken; the files were deleted but since the file handles are still
       * open the kernel will keep the data around.
       */
      public static class FileLeak implements ListenableFileSystem.OnPostOpen, ListenableFileSystem.OnPreClose, ListenableFileSystem.OnPreDelete
      {
          @Nullable
          private final IdentityHashMap<FileChannel, Throwable> whereDidChannelsComeFrom;
          private final Map<Path, Set<FileChannel>> pathToChannels = new HashMap<>();
  
          public FileLeak(boolean trackOpenSource)
          {
              whereDidChannelsComeFrom = trackOpenSource ? new IdentityHashMap<>() : null;
          }
  
          public FileLeak()
          {
              this(false);
          }
  
          @Override
          public synchronized void postOpen(Path path,
                                            Set<? extends OpenOption> options,
                                            FileAttribute<?>[] attrs,
                                            FileChannel channel)
          {
              pathToChannels.computeIfAbsent(path, i -> Collections.newSetFromMap(new IdentityHashMap<>())).add(channel);
              if (whereDidChannelsComeFrom != null)
                  whereDidChannelsComeFrom.put(channel, new Throwable("here"));
          }
  
          @Override
          public synchronized void preClose(Path path, FileChannel channel)
          {
              Set<FileChannel> channels = pathToChannels.get(path);
              if (channels == null || !channels.remove(channel))
                  return; // listener was added after the open?
              if (channels.isEmpty())
                  pathToChannels.remove(path);
          }
  
          @Override
          public synchronized void preDelete(Path path)
          {
              var cs = pathToChannels.get(path);
              if (cs == null) return;
              AssertionError e = new AssertionError("File leak (delete before close) detected on path " + path + "; " + cs.size() + " open handels detected");
              if (whereDidChannelsComeFrom != null)
              {
                  var sources = cs.stream().map(whereDidChannelsComeFrom::get).collect(Collectors.toList());
                  sources.forEach(e::addSuppressed);
  
              }
              throw e;
          }
      }
  }
  