Github user GJL commented on a diff in the pull request:
https://github.com/apache/flink/pull/5091#discussion_r155758219
--- Diff:
flink-runtime/src/main/java/org/apache/flink/runtime/jobmaster/slotpool/SlotSharingManager.java
---
@@ -0,0 +1,722 @@
+/*
+ * 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.jobmaster.slotpool;
+
+import org.apache.flink.annotation.VisibleForTesting;
+import org.apache.flink.runtime.jobmaster.LogicalSlot;
+import org.apache.flink.runtime.jobmaster.SlotContext;
+import org.apache.flink.runtime.jobmaster.SlotOwner;
+import org.apache.flink.runtime.jobmaster.SlotRequestId;
+import org.apache.flink.runtime.instance.SlotSharingGroupId;
+import org.apache.flink.runtime.jobmanager.scheduler.Locality;
+import org.apache.flink.runtime.taskmanager.TaskManagerLocation;
+import org.apache.flink.util.AbstractID;
+import org.apache.flink.util.FlinkException;
+import org.apache.flink.util.Preconditions;
+
+import javax.annotation.Nullable;
+
+import java.util.AbstractCollection;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.Iterator;
+import java.util.Map;
+import java.util.Objects;
+import java.util.Set;
+import java.util.concurrent.CompletableFuture;
+
+/**
+ * Manager which is responsible for slot sharing. Slot sharing allows to
run different
+ * tasks in the same slot and to realize co-location constraints.
+ *
+ * <p>The SlotSharingManager allows to create a hierarchy of {@link
TaskSlot} such that
+ * every {@link TaskSlot} is uniquely identified by a {@link
SlotRequestId} identifying
+ * the request for the TaskSlot and a {@link AbstractID} identifying the
task or the
+ * co-location constraint running in this slot.
+ *
+ * <p>The {@link TaskSlot} hierarchy is implemented by {@link
MultiTaskSlot} and
+ * {@link SingleTaskSlot}. The former class represents inner nodes which
can contain
+ * a number of other {@link TaskSlot} and the latter class represents the
leave nodes.
--- End diff --
nit: *leaf nodes*
---
