Github user StefanRRichter commented on a diff in the pull request:

    https://github.com/apache/flink/pull/5239#discussion_r169898668
  
    --- Diff: 
flink-runtime/src/main/java/org/apache/flink/runtime/state/SnapshotDirectory.java
 ---
    @@ -0,0 +1,172 @@
    +/*
    + * 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.flink.runtime.state;
    +
    +import org.apache.flink.core.fs.FileStatus;
    +import org.apache.flink.core.fs.FileSystem;
    +import org.apache.flink.core.fs.Path;
    +
    +import javax.annotation.Nonnull;
    +
    +import java.io.IOException;
    +import java.util.concurrent.atomic.AtomicReference;
    +
    +/**
    + * This class represents a directory that is the target for a state 
snapshot. This class provides some method that
    + * simplify resource management when dealing with such directories, e.g. 
it can produce a {@link DirectoryStateHandle}
    + * when the snapshot is completed and disposal considers whether or not a 
snapshot was already completed. For a
    + * completed snapshot, the ownership for cleanup is transferred to the 
created directory state handle. For incomplete
    + * snapshots, calling {@link #deleteIfIncompleteSnapshot()} will delete 
the underlying directory resource.
    + */
    +public class SnapshotDirectory {
    +
    +   /**
    +    * Lifecycle stages of a snapshot directory.
    +    */
    +   enum State {
    +           ONGOING, COMPLETED, DELETED
    +   }
    +
    +   /** This path describes the underlying directory for the snapshot. */
    +   @Nonnull
    +   private final Path directory;
    +
    +   /** The filesystem that contains the snapshot directory. */
    +   @Nonnull
    +   private final FileSystem fileSystem;
    --- End diff --
    
    In this class, I would keep it because it is used in several operations and 
obtaining the `FileSystem` from `Path` looks like it might not be a cheap 
operation. So this is more like a cache, or in case that you already have the 
`FileSystem` when constructing the object.


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