Github user sihuazhou commented on a diff in the pull request:
https://github.com/apache/flink/pull/6228#discussion_r199325117
--- Diff:
flink-runtime/src/main/java/org/apache/flink/runtime/state/InternalPriorityQueue.java
---
@@ -0,0 +1,99 @@
+/*
+ * 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.annotation.Internal;
+import org.apache.flink.util.CloseableIterator;
+
+import javax.annotation.Nonnegative;
+import javax.annotation.Nonnull;
+import javax.annotation.Nullable;
+
+import java.util.Collection;
+
+/**
+ * Interface for collection that gives in order access to elements w.r.t
their priority.
+ *
+ * @param <T> type of elements in the ordered set.
+ */
+@Internal
+public interface InternalPriorityQueue<T> {
+
+ /**
+ * Retrieves and removes the first element (w.r.t. the order) of this
set,
+ * or returns {@code null} if this set is empty.
+ *
+ * @return the first element of this ordered set, or {@code null} if
this set is empty.
+ */
+ @Nullable
+ T poll();
+
+ /**
+ * Retrieves, but does not remove, the element (w.r.t. order) of this
set,
+ * or returns {@code null} if this set is empty.
+ *
+ * @return the first element (w.r.t. order) of this ordered set, or
{@code null} if this set is empty.
+ */
+ @Nullable
+ T peek();
+
+ /**
+ * Adds the given element to the set, if it is not already contained.
+ *
+ * @param toAdd the element to add to the set.
+ * @return <code>true</> if the operation changed the head element or
if is it unclear if the head element changed.
+ * Only returns <code>false</> iff the head element was not changed by
this operation.
+ */
+ boolean add(@Nonnull T toAdd);
+
+ /**
+ * Removes the given element from the set, if is contained in the set.
+ *
+ * @param toRemove the element to remove.
+ * @return <code>true</> if the operation changed the head element or
if is it unclear if the head element changed.
--- End diff --
nit: unclosed HTML tag `<code>`
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