[GitHub] [flink] zhuzhurk commented on a change in pull request #13205: [FLINK-17330[runtime] Merge cyclic dependent pipelined regions into one region

[GitBox <gi...@apache.org>]

zhuzhurk commented on a change in pull request #13205:
URL: https://github.com/apache/flink/pull/13205#discussion_r475388935



##########
File path: flink-runtime/src/main/java/org/apache/flink/runtime/executiongraph/failover/flip1/StronglyConnectedComponentsComputeUtils.java
##########
@@ -0,0 +1,121 @@
+/*
+ * 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.executiongraph.failover.flip1;
+
+import org.apache.flink.api.java.tuple.Tuple2;
+
+import java.util.ArrayDeque;
+import java.util.Arrays;
+import java.util.Deque;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Set;
+import java.util.concurrent.atomic.AtomicInteger;
+
+/**
+ * Utility for computing strongly connected components.
+ *
+ * <p>The computation is an implementation of Tarjan's algorithm.
+ *
+ * <p>Ref: https://en.wikipedia.org/wiki/Tarjan%27s_strongly_connected_components_algorithm.
+ */
+public final class StronglyConnectedComponentsComputeUtils {
+
+	static Set<Set<Integer>> computeStronglyConnectedComponents(final int numVertex, final List<List<Integer>> outEdges) {
+		final Set<Set<Integer>> stronglyConnectedComponents = new HashSet<>();
+
+		final int[] vertexIndices = new int[numVertex];
+		Arrays.fill(vertexIndices, -1);
+
+		final int[] vertexLowLinks = new int[numVertex];
+		final Deque<Integer> stack = new ArrayDeque<>(numVertex);

Review comment:
       renamed it as `visitingStack`




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