HADOOP-18105 Implement buffer pooling with weak references (#4263)

part of HADOOP-18103.
Required for vectored IO feature. None of current buffer pool
implementation is complete. ElasticByteBufferPool doesn't use
weak references and could lead to memory leak errors and
DirectBufferPool doesn't support caller preferences of direct
and heap buffers and has only fixed length buffer implementation.

Contributed By: Mukund Thakur

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/ByteBufferPool.java

@@ -45,4 +45,9 @@ public interface ByteBufferPool {
    * @param buffer    a direct bytebuffer
    */
   void putBuffer(ByteBuffer buffer);
+
+  /**
+   * Clear the buffer pool thus releasing all the buffers.
+   */
+  default void release() { }
 }

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/ElasticByteBufferPool.java

@@ -36,8 +36,8 @@
  */
 @InterfaceAudience.Public
 @InterfaceStability.Stable
-public final class ElasticByteBufferPool implements ByteBufferPool {
-  private static final class Key implements Comparable<Key> {
+public class ElasticByteBufferPool implements ByteBufferPool {
+  protected static final class Key implements Comparable<Key> {
     private final int capacity;
     private final long insertionTime;
 

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/WeakReferencedElasticByteBufferPool.java

@@ -0,0 +1,155 @@
+/**
+ * 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.io;
+
+import java.lang.ref.WeakReference;
+import java.nio.ByteBuffer;
+import java.util.Map;
+import java.util.TreeMap;
+
+import org.apache.hadoop.classification.InterfaceAudience;
+import org.apache.hadoop.classification.InterfaceStability;
+import org.apache.hadoop.classification.VisibleForTesting;
+
+/**
+ * Buffer pool implementation which uses weak references to store
+ * buffers in the pool, such that they are garbage collected when
+ * there are no references to the buffer during a gc run. This is
+ * important as direct buffers don't get garbage collected automatically
+ * during a gc run as they are not stored on heap memory.
+ * Also the buffers are stored in a tree map which helps in returning
+ * smallest buffer whose size is just greater than requested length.
+ * This is a thread safe implementation.
+ */
+@InterfaceAudience.Private
+@InterfaceStability.Unstable
+public final class WeakReferencedElasticByteBufferPool extends ElasticByteBufferPool {
+
+  /**
+   * Map to store direct byte buffers of different sizes in the pool.
+   * Used tree map such that we can return next greater than capacity
+   * buffer if buffer with exact capacity is unavailable.
+   * This must be accessed in synchronized blocks.
+   */
+  private final TreeMap<Key, WeakReference<ByteBuffer>> directBuffers =
+          new TreeMap<>();
+
+  /**
+   * Map to store heap based byte buffers of different sizes in the pool.
+   * Used tree map such that we can return next greater than capacity
+   * buffer if buffer with exact capacity is unavailable.
+   * This must be accessed in synchronized blocks.
+   */
+  private final TreeMap<Key, WeakReference<ByteBuffer>> heapBuffers =
+          new TreeMap<>();
+
+  /**
+   * Method to get desired buffer tree.
+   * @param isDirect whether the buffer is heap based or direct.
+   * @return corresponding buffer tree.
+   */
+  private TreeMap<Key, WeakReference<ByteBuffer>> getBufferTree(boolean isDirect) {
+    return isDirect
+            ? directBuffers
+            : heapBuffers;
+  }
+
+  /**
+   * {@inheritDoc}
+   *
+   * @param direct whether we want a direct byte buffer or a heap one.
+   * @param length length of requested buffer.
+   * @return returns equal or next greater than capacity buffer from
+   * pool if already available and not garbage collected else creates
+   * a new buffer and return it.
+   */
+  @Override
+  public synchronized ByteBuffer getBuffer(boolean direct, int length) {
+    TreeMap<Key, WeakReference<ByteBuffer>> buffersTree = getBufferTree(direct);
+
+    // Scan the entire tree and remove all weak null references.
+    buffersTree.entrySet().removeIf(next -> next.getValue().get() == null);
+
+    Map.Entry<Key, WeakReference<ByteBuffer>> entry =
+            buffersTree.ceilingEntry(new Key(length, 0));
+    // If there is no buffer present in the pool with desired size.
+    if (entry == null) {
+      return direct ? ByteBuffer.allocateDirect(length) :
+                      ByteBuffer.allocate(length);
+    }
+    // buffer is available in the pool and not garbage collected.
+    WeakReference<ByteBuffer> bufferInPool = entry.getValue();
+    buffersTree.remove(entry.getKey());
+    ByteBuffer buffer = bufferInPool.get();
+    if (buffer != null) {
+      return buffer;
+    }
+    // buffer was in pool but already got garbage collected.
+    return direct
+            ? ByteBuffer.allocateDirect(length)
+            : ByteBuffer.allocate(length);
+  }
+
+  /**
+   * Return buffer to the pool.
+   * @param buffer buffer to be returned.
+   */
+  @Override
+  public synchronized void putBuffer(ByteBuffer buffer) {
+    buffer.clear();
+    TreeMap<Key, WeakReference<ByteBuffer>> buffersTree = getBufferTree(buffer.isDirect());
+    // Buffers are indexed by (capacity, time).
+    // If our key is not unique on the first try, we try again, since the
+    // time will be different.  Since we use nanoseconds, it's pretty
+    // unlikely that we'll loop even once, unless the system clock has a
+    // poor granularity or multi-socket systems have clocks slightly out
+    // of sync.
+    while (true) {
+      Key keyToInsert = new Key(buffer.capacity(), System.nanoTime());
+      if (!buffersTree.containsKey(keyToInsert)) {
+        buffersTree.put(keyToInsert, new WeakReference<>(buffer));
+        return;
+      }
+    }
+  }
+
+  /**
+   * Clear the buffer pool thus releasing all the buffers.
+   * The caller must remove all references of
+   * existing buffers before calling this method to avoid
+   * memory leaks.
+   */
+  @Override
+  public synchronized void release() {
+    heapBuffers.clear();
+    directBuffers.clear();
+  }
+
+  /**
+   * Get current buffers count in the pool.
+   * @param isDirect whether we want to count the heap or direct buffers.
+   * @return count of buffers.
+   */
+  @VisibleForTesting
+  public synchronized int getCurrentBuffersCount(boolean isDirect) {
+    return isDirect
+            ? directBuffers.size()
+            : heapBuffers.size();
+  }
+}

hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/io/TestMoreWeakReferencedElasticByteBufferPool.java

@@ -0,0 +1,97 @@
+/**
+ * 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.io;
+
+import java.nio.BufferOverflowException;
+import java.nio.ByteBuffer;
+
+import org.assertj.core.api.Assertions;
+import org.junit.Test;
+
+import org.apache.hadoop.test.HadoopTestBase;
+
+import static org.apache.hadoop.test.LambdaTestUtils.intercept;
+
+/**
+ * Non parameterized tests for {@code WeakReferencedElasticByteBufferPool}.
+ */
+public class TestMoreWeakReferencedElasticByteBufferPool
+        extends HadoopTestBase {
+
+  @Test
+  public void testMixedBuffersInPool() {
+    WeakReferencedElasticByteBufferPool pool = new WeakReferencedElasticByteBufferPool();
+    ByteBuffer buffer1 = pool.getBuffer(true, 5);
+    ByteBuffer buffer2 = pool.getBuffer(true, 10);
+    ByteBuffer buffer3 = pool.getBuffer(false, 5);
+    ByteBuffer buffer4 = pool.getBuffer(false, 10);
+    ByteBuffer buffer5 = pool.getBuffer(true, 15);
+
+    assertBufferCounts(pool, 0, 0);
+    pool.putBuffer(buffer1);
+    pool.putBuffer(buffer2);
+    assertBufferCounts(pool, 2, 0);
+    pool.putBuffer(buffer3);
+    assertBufferCounts(pool, 2, 1);
+    pool.putBuffer(buffer5);
+    assertBufferCounts(pool, 3, 1);
+    pool.putBuffer(buffer4);
+    assertBufferCounts(pool, 3, 2);
+    pool.release();
+    assertBufferCounts(pool, 0, 0);
+
+  }
+
+  @Test
+  public void testUnexpectedBufferSizes() throws Exception {
+    WeakReferencedElasticByteBufferPool pool = new WeakReferencedElasticByteBufferPool();
+    ByteBuffer buffer1 = pool.getBuffer(true, 0);
+
+    // try writing a random byte in a 0 length buffer.
+    // Expected exception as buffer requested is of size 0.
+    intercept(BufferOverflowException.class,
+        () -> buffer1.put(new byte[1]));
+
+    // Expected IllegalArgumentException as negative length buffer is requested.
+    intercept(IllegalArgumentException.class,
+        () -> pool.getBuffer(true, -5));
+
+    // test returning null buffer to the pool.
+    intercept(NullPointerException.class,
+        () -> pool.putBuffer(null));
+  }
+
+  /**
+   * Utility method to assert counts of direct and heap buffers in
+   * the given buffer pool.
+   * @param pool buffer pool.
+   * @param numDirectBuffersExpected expected number of direct buffers.
+   * @param numHeapBuffersExpected expected number of heap buffers.
+   */
+  private void assertBufferCounts(WeakReferencedElasticByteBufferPool pool,
+                                  int numDirectBuffersExpected,
+                                  int numHeapBuffersExpected) {
+    Assertions.assertThat(pool.getCurrentBuffersCount(true))
+            .describedAs("Number of direct buffers in pool")
+            .isEqualTo(numDirectBuffersExpected);
+    Assertions.assertThat(pool.getCurrentBuffersCount(false))
+            .describedAs("Number of heap buffers in pool")
+            .isEqualTo(numHeapBuffersExpected);
+  }
+}