Github user tillrohrmann commented on a diff in the pull request:
https://github.com/apache/flink/pull/5239#discussion_r168477978
--- Diff:
flink-runtime/src/main/java/org/apache/flink/runtime/state/LocalRecoveryDirectoryProvider.java
---
@@ -0,0 +1,112 @@
+/*
+ * 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.util.Preconditions;
+
+import java.io.File;
+import java.io.Serializable;
+import java.util.Arrays;
+import java.util.UUID;
+import java.util.concurrent.atomic.AtomicInteger;
+
+/**
+ * Provides root directories and the subtask-specific path to build
directories for file-based local recovery. Calls
+ * to {@link #nextRootDirectory()} rotate over all available root
directories. this class is thread-safe.
+ */
+public class LocalRecoveryDirectoryProvider implements Serializable {
+
+ private static final long serialVersionUID = 1L;
+
+ /** All available root directories that this can potentially deliver. */
+ private final File[] rootDirectories;
+
+ /** A subtask-specific string that describes a path to it's local state
from a given checkpoint root. */
+ private final String subtaskSpecificPath;
+
+ /** Current index for rotational selection of delivered root dirs. */
+ private AtomicInteger idx;
+
+ public LocalRecoveryDirectoryProvider(File rootDir, String
subtaskSpecificPath) {
+ this(new File[]{rootDir}, subtaskSpecificPath);
+ }
+
+ public LocalRecoveryDirectoryProvider(File[] rootDirectories, String
subtaskSpecificPath) {
+
+ this.rootDirectories =
Preconditions.checkNotNull(rootDirectories);
+ this.subtaskSpecificPath =
Preconditions.checkNotNull(subtaskSpecificPath);
+ Preconditions.checkArgument(rootDirectories.length > 0);
+
+ for (File directory : rootDirectories) {
+ Preconditions.checkNotNull(directory);
+ if (!directory.isDirectory()) {
+ throw new IllegalStateException("Local recovery
root directory " + directory + " does not exist!");
+ }
+ }
+
+ this.idx = new AtomicInteger(-1);
+ }
+
+ /**
+ * Returns the next root directory w.r.t. our rotation over all
available root dirs.
+ */
+ public File nextRootDirectory() {
+ return rootDirectories[(idx.incrementAndGet() &
Integer.MAX_VALUE) % rootDirectories.length];
--- End diff --
Nice trick :-)
---
