From 6d5cbbdc25562fca16dae7e76ec62fe3beb52f90 Mon Sep 17 00:00:00 2001
From: Andrew Kyle Purtell <apurtell@apache.org>
Date: Tue, 5 May 2009 09:13:05 +0000
Subject: [PATCH] HBASE-1341 HTable pooler

git-svn-id: https://svn.apache.org/repos/asf/hadoop/hbase/trunk@771633 13f79535-47bb-0310-9956-ffa450edef68
---
 CHANGES.txt                                   |   1 +
 .../hadoop/hbase/client/HTablePool.java       | 127 ++++++++++++++++++
 2 files changed, 128 insertions(+)
 create mode 100755 src/java/org/apache/hadoop/hbase/client/HTablePool.java

diff --git a/CHANGES.txt b/CHANGES.txt
index 33148801ec6..825fba16e07 100644
--- a/CHANGES.txt
+++ b/CHANGES.txt
@@ -198,6 +198,7 @@ Release 0.20.0 - Unreleased
    HBASE-889   The current Thrift API does not allow a new scanner to be
                created without supplying a column list unlike the other APIs.
                (Tim Sell via Stack)
+   HBASE-1341  HTable pooler
 
 Release 0.19.0 - 01/21/2009
   INCOMPATIBLE CHANGES
diff --git a/src/java/org/apache/hadoop/hbase/client/HTablePool.java b/src/java/org/apache/hadoop/hbase/client/HTablePool.java
new file mode 100755
index 00000000000..301982e43f1
--- /dev/null
+++ b/src/java/org/apache/hadoop/hbase/client/HTablePool.java
@@ -0,0 +1,127 @@
+/**
+ * Copyright 2009 The Apache Software Foundation
+ *
+ * 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.hadoop.hbase.client;
+
+import java.io.IOException;
+import java.util.ArrayDeque;
+/* using a stack instead of a FIFO might have some small positive performance
+   impact wrt. cache */
+import java.util.Deque;
+import java.util.Map;
+import java.util.TreeMap;
+
+import org.apache.hadoop.hbase.util.Bytes;
+
+/**
+ * A simple pool of HTable instances.
+ * <p>
+ * The default pool size is 10.
+ */
+public class HTablePool {
+  private static final Map<byte[], HTablePool> poolMap = 
+    new TreeMap<byte[], HTablePool>(Bytes.BYTES_COMPARATOR);
+
+  private final byte[] tableName;
+  private final Deque<HTable> pool;
+  private final int maxSize;
+
+  /**
+   * Get a shared table pool.
+   * @param tableName the table name
+   * @return the table pool
+   */
+  public static HTablePool getPool(byte[] tableName) {
+    return getPool(tableName, 10);
+  }
+
+  /**
+   * Get a shared table pool.
+   * <p>
+   * NOTE: <i>maxSize</i> is advisory. If the pool does not yet exist, a new
+   * shared pool will be allocated with <i>maxSize</i> as the size limit.
+   * However, if the shared pool already exists, and was created with a 
+   * different (or default) value for <i>maxSize</i>, it will not be changed.
+   * @param tableName the table name
+   * @param maxSize the maximum size of the pool
+   * @return the table pool
+   */
+  public static HTablePool getPool(byte[] tableName, int maxSize) {
+    synchronized (poolMap) {
+      HTablePool pool = poolMap.get(tableName);
+      if (pool == null) {
+        pool = new HTablePool(tableName, maxSize);
+        poolMap.put(tableName, pool);
+      }
+      return pool;
+    }
+  }
+
+  /**
+   * Constructor
+   * @param tableName the table name
+   */
+  public HTablePool(byte[] tableName) {
+    this.tableName = tableName;
+    this.maxSize = 10;
+    this.pool = new ArrayDeque<HTable>(this.maxSize);
+  }
+
+  /**
+   * Constructor
+   * @param tableName the table name
+   * @param maxSize maximum pool size
+   */
+  public HTablePool(byte[] tableName, int maxSize) {
+    this.tableName = tableName;
+    this.maxSize = maxSize;
+    this.pool = new ArrayDeque<HTable>(this.maxSize);
+  }
+
+  /**
+   * Get a HTable instance, possibly from the pool, if one is available.
+   * @return HTable a HTable instance
+   * @throws IOException
+   */
+  public HTable get() throws IOException {
+    synchronized (pool) {
+      // peek then pop inside a synchronized block avoids the overhead of a
+      // NoSuchElementException
+      HTable table = pool.peek();
+      if (table != null) {
+        return pool.pop();
+      }
+    }
+    return new HTable(tableName);
+  }
+
+  /**
+   * Return a HTable instance to the pool.
+   * @param table a HTable instance
+   */
+  public void put(HTable table) {
+    synchronized (pool) {
+      if (pool.size() < maxSize) {
+        pool.push(table);
+      }
+    }
+  }
+
+}