Github user poornachandra commented on a diff in the pull request:
https://github.com/apache/incubator-tephra/pull/32#discussion_r100042435
--- Diff:
tephra-hbase-compat-1.1-base/src/main/java/org/apache/tephra/hbase/txprune/PruneUpperBoundWriterSupplier.java
---
@@ -0,0 +1,78 @@
+/*
+ * 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.tephra.hbase.txprune;
+
+
+import com.google.common.base.Supplier;
+import org.apache.commons.logging.Log;
+import org.apache.commons.logging.LogFactory;
+
+/**
+ * Supplies instances of {@link PruneUpperBoundWriter} implementations.
+ */
+public class PruneUpperBoundWriterSupplier implements
Supplier<PruneUpperBoundWriter> {
+ private static final Log LOG =
LogFactory.getLog(PruneUpperBoundWriterSupplier.class);
+
+ private static volatile PruneUpperBoundWriter instance;
+ private static volatile int refCount = 0;
+ private static final Object lock = new Object();
+
+ private final DataJanitorState dataJanitorState;
+ private final long pruneFlushInterval;
+
+ public PruneUpperBoundWriterSupplier(DataJanitorState dataJanitorState,
long pruneFlushInterval) {
+ this.dataJanitorState = dataJanitorState;
+ this.pruneFlushInterval = pruneFlushInterval;
+ }
+
+ @Override
+ public PruneUpperBoundWriter get() {
+ synchronized (lock) {
--- End diff --
We can make an `instance == null` check outside the lock. In case instance
is not null just increment refCount and return.
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