Github user aljoscha commented on a diff in the pull request:
https://github.com/apache/flink/pull/4764#discussion_r143685852
--- Diff: flink-core/src/main/java/org/apache/flink/util/ResourceGuard.java
---
@@ -0,0 +1,152 @@
+/*
+ * 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.util;
+
+import java.io.IOException;
+import java.io.Serializable;
+import java.util.concurrent.atomic.AtomicBoolean;
+
+/**
+ * This class is a guard for shared resources with the following
invariants. The resource can be acquired by multiple
+ * clients in parallel through the {@link #acquireResource()} call. As a
result of the call, each client gets a
+ * {@link Lease}. The {@link #close()} method of the lease releases the
resources and reduces the client count in
+ * the {@link ResourceGuard} object.
+ * The protected resource should only be disposed once the corresponding
resource guard is successfully closed, but
+ * the guard can only be closed once all clients that acquired a lease for
the guarded resource have released it.
+ * Before this is happened, the call to {@link #close()} will block until
the zero-open-leases condition is triggered.
--- End diff --
nit "Before this has happened"
---
