Issue #1861 - Limit total bytes pooled by ByteBufferPools.

Implemented a limit for the total memory retained by the
ByteBufferPool for both direct and heap buffers.

Signed-off-by: Simone Bordet <simone.bordet@gmail.com>

jetty-io/src/main/java/org/eclipse/jetty/io/AbstractByteBufferPool.java

@@ -0,0 +1,93 @@
+//
+//  ========================================================================
+//  Copyright (c) 1995-2019 Mort Bay Consulting Pty. Ltd.
+//  ------------------------------------------------------------------------
+//  All rights reserved. This program and the accompanying materials
+//  are made available under the terms of the Eclipse Public License v1.0
+//  and Apache License v2.0 which accompanies this distribution.
+//
+//      The Eclipse Public License is available at
+//      http://www.eclipse.org/legal/epl-v10.html
+//
+//      The Apache License v2.0 is available at
+//      http://www.opensource.org/licenses/apache2.0.php
+//
+//  You may elect to redistribute this code under either of these licenses.
+//  ========================================================================
+//
+
+package org.eclipse.jetty.io;
+
+import java.nio.ByteBuffer;
+import java.util.concurrent.atomic.AtomicLong;
+
+import org.eclipse.jetty.util.annotation.ManagedObject;
+import org.eclipse.jetty.util.annotation.ManagedOperation;
+
+@ManagedObject
+abstract class AbstractByteBufferPool implements ByteBufferPool
+{
+    private final int _factor;
+    private final int _maxQueueLength;
+    private final long _maxHeapMemory;
+    private final AtomicLong _heapMemory = new AtomicLong();
+    private final long _maxDirectMemory;
+    private final AtomicLong _directMemory = new AtomicLong();
+
+    protected AbstractByteBufferPool(int factor, int maxQueueLength, long maxHeapMemory, long maxDirectMemory)
+    {
+        _factor = factor <= 0 ? 1024 : factor;
+        _maxQueueLength = maxQueueLength;
+        _maxHeapMemory = maxHeapMemory;
+        _maxDirectMemory = maxDirectMemory;
+    }
+
+    protected int getCapacityFactor()
+    {
+        return _factor;
+    }
+
+    protected int getMaxQueueLength()
+    {
+        return _maxQueueLength;
+    }
+
+    protected void decrementMemory(ByteBuffer buffer)
+    {
+        AtomicLong memory = buffer.isDirect() ? _directMemory : _heapMemory;
+        memory.addAndGet(-buffer.capacity());
+    }
+
+    protected boolean incrementMemory(ByteBuffer buffer)
+    {
+        boolean direct = buffer.isDirect();
+        int capacity = buffer.capacity();
+        long maxMemory = direct ? _maxDirectMemory : _maxHeapMemory;
+        AtomicLong memory = direct ? _directMemory : _heapMemory;
+        if (maxMemory <= 0)
+            return true;
+        while (true)
+        {
+            long current = memory.get();
+            long value = current + capacity;
+            if (value > maxMemory)
+                return false;
+            if (memory.compareAndSet(current, value))
+                return true;
+        }
+    }
+
+    @ManagedOperation(value = "Returns the memory occupied by this ByteBufferPool in bytes", impact = "INFO")
+    public long getMemory(boolean direct)
+    {
+        AtomicLong memory = direct ? _directMemory : _heapMemory;
+        return memory.get();
+    }
+
+    @ManagedOperation(value = "Clears this ByteBufferPool", impact = "ACTION")
+    public void clear()
+    {
+        _heapMemory.set(0);
+        _directMemory.set(0);
+    }
+}

jetty-io/src/main/java/org/eclipse/jetty/io/ArrayByteBufferPool.java

@@ -19,9 +19,9 @@
 package org.eclipse.jetty.io;
 
 import java.nio.ByteBuffer;
+import java.util.function.IntFunction;
 
 import org.eclipse.jetty.util.annotation.ManagedObject;
-import org.eclipse.jetty.util.annotation.ManagedOperation;
 
 /**
  * <p>A ByteBuffer pool where ByteBuffers are held in queues that are held in array elements.</p>
@@ -30,19 +30,18 @@ import org.eclipse.jetty.util.annotation.ManagedOperation;
  * 2048, and so on.</p>
  */
 @ManagedObject
-public class ArrayByteBufferPool implements ByteBufferPool
+public class ArrayByteBufferPool extends AbstractByteBufferPool
 {
     private final int _minCapacity;
     private final ByteBufferPool.Bucket[] _direct;
     private final ByteBufferPool.Bucket[] _indirect;
-    private final int _factor;
 
     /**
      * Creates a new ArrayByteBufferPool with a default configuration.
      */
     public ArrayByteBufferPool()
     {
-        this(-1, -1, -1, -1);
+        this(-1, -1, -1);
     }
 
     /**
@@ -54,7 +53,7 @@ public class ArrayByteBufferPool implements ByteBufferPool
      */
     public ArrayByteBufferPool(int minCapacity, int factor, int maxCapacity)
     {
-        this(minCapacity, factor, maxCapacity, -1);
+        this(minCapacity, factor, maxCapacity, -1, -1, -1);
     }
 
     /**
@@ -67,68 +66,100 @@ public class ArrayByteBufferPool implements ByteBufferPool
      */
     public ArrayByteBufferPool(int minCapacity, int factor, int maxCapacity, int maxQueueLength)
     {
+        this(minCapacity, factor, maxCapacity, maxQueueLength, -1, -1);
+    }
+
+    /**
+     * Creates a new ArrayByteBufferPool with the given configuration.
+     *
+     * @param minCapacity the minimum ByteBuffer capacity
+     * @param factor the capacity factor
+     * @param maxCapacity the maximum ByteBuffer capacity
+     * @param maxQueueLength the maximum ByteBuffer queue length
+     * @param maxHeapMemory the max heap memory in bytes
+     * @param maxDirectMemory the max direct memory in bytes
+     */
+    public ArrayByteBufferPool(int minCapacity, int factor, int maxCapacity, int maxQueueLength, long maxHeapMemory, long maxDirectMemory)
+    {
+        super(factor, maxQueueLength, maxHeapMemory, maxDirectMemory);
+
+        factor = getCapacityFactor();
         if (minCapacity <= 0)
             minCapacity = 0;
-        if (factor <= 0)
-            factor = 1024;
         if (maxCapacity <= 0)
             maxCapacity = 64 * 1024;
         if ((maxCapacity % factor) != 0 || factor >= maxCapacity)
             throw new IllegalArgumentException("The capacity factor must be a divisor of maxCapacity");
         _minCapacity = minCapacity;
-        _factor = factor;
 
         int length = maxCapacity / factor;
         _direct = new ByteBufferPool.Bucket[length];
         _indirect = new ByteBufferPool.Bucket[length];
-
-        int capacity = 0;
-        for (int i = 0; i < _direct.length; ++i)
-        {
-            capacity += _factor;
-            _direct[i] = new ByteBufferPool.Bucket(this, capacity, maxQueueLength);
-            _indirect[i] = new ByteBufferPool.Bucket(this, capacity, maxQueueLength);
-        }
     }
 
     @Override
     public ByteBuffer acquire(int size, boolean direct)
     {
-        ByteBufferPool.Bucket bucket = bucketFor(size, direct);
+        ByteBufferPool.Bucket bucket = bucketFor(size, direct, null);
         if (bucket == null)
-            return newByteBuffer(size, direct);
+        {
-        return bucket.acquire(direct);
+            int capacity = size < _minCapacity ? size : (bucketFor(size) + 1) * getCapacityFactor();
+            return newByteBuffer(capacity, direct);
+        }
+        ByteBuffer buffer = bucket.acquire(direct);
+        decrementMemory(buffer);
+        return buffer;
     }
 
     @Override
     public void release(ByteBuffer buffer)
     {
-        if (buffer != null)
+        if (buffer == null)
-        {
+            return;
-            ByteBufferPool.Bucket bucket = bucketFor(buffer.capacity(), buffer.isDirect());
+        ByteBufferPool.Bucket bucket = bucketFor(buffer.capacity(), buffer.isDirect(), this::newBucket);
-            if (bucket != null)
+        if (bucket != null && incrementMemory(buffer))
-                bucket.release(buffer);
+            bucket.release(buffer);
-        }
     }
 
-    @ManagedOperation(value = "Clears this ByteBufferPool", impact = "ACTION")
+    private Bucket newBucket(int key)
+    {
+        return new Bucket(this, key * getCapacityFactor(), getMaxQueueLength());
+    }
+
+    @Override
     public void clear()
     {
+        super.clear();
         for (int i = 0; i < _direct.length; ++i)
         {
-            _direct[i].clear();
+            Bucket bucket = _direct[i];
-            _indirect[i].clear();
+            if (bucket != null)
+                bucket.clear();
+            _direct[i] = null;
+            bucket = _indirect[i];
+            if (bucket != null)
+                bucket.clear();
+            _indirect[i] = null;
         }
     }
 
-    private ByteBufferPool.Bucket bucketFor(int capacity, boolean direct)
+    private int bucketFor(int capacity)
     {
-        if (capacity <= _minCapacity)
+        return (capacity - 1) / getCapacityFactor();
+    }
+
+    private ByteBufferPool.Bucket bucketFor(int capacity, boolean direct, IntFunction<Bucket> newBucket)
+    {
+        if (capacity < _minCapacity)
             return null;
-        int b = (capacity - 1) / _factor;
+        int b = bucketFor(capacity);
         if (b >= _direct.length)
             return null;
-        return bucketsFor(direct)[b];
+        Bucket[] buckets = bucketsFor(direct);
+        Bucket bucket = buckets[b];
+        if (bucket == null && newBucket != null)
+            buckets[b] = bucket = newBucket.apply(b + 1);
+        return bucket;
     }
 
     // Package local for testing

jetty-io/src/main/java/org/eclipse/jetty/io/ByteBufferPool.java

@@ -131,7 +131,7 @@ public interface ByteBufferPool
         }
     }
 
-    class Bucket
+    public static class Bucket
     {
         private final Deque<ByteBuffer> _queue = new ConcurrentLinkedDeque<>();
         private final ByteBufferPool _pool;

jetty-io/src/main/java/org/eclipse/jetty/io/MappedByteBufferPool.java

@@ -22,10 +22,10 @@ import java.nio.ByteBuffer;
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.ConcurrentMap;
 import java.util.concurrent.atomic.AtomicInteger;
+import java.util.function.Function;
 
 import org.eclipse.jetty.util.BufferUtil;
 import org.eclipse.jetty.util.annotation.ManagedObject;
-import org.eclipse.jetty.util.annotation.ManagedOperation;
 
 /**
  * <p>A ByteBuffer pool where ByteBuffers are held in queues that are held in a Map.</p>
@@ -34,12 +34,11 @@ import org.eclipse.jetty.util.annotation.ManagedOperation;
  * queue of ByteBuffers each of capacity 2048, and so on.</p>
  */
 @ManagedObject
-public class MappedByteBufferPool implements ByteBufferPool
+public class MappedByteBufferPool extends AbstractByteBufferPool
 {
-    private final ConcurrentMap<Integer, Bucket> directBuffers = new ConcurrentHashMap<>();
+    private final ConcurrentMap<Integer, Bucket> _directBuffers = new ConcurrentHashMap<>();
-    private final ConcurrentMap<Integer, Bucket> heapBuffers = new ConcurrentHashMap<>();
+    private final ConcurrentMap<Integer, Bucket> _heapBuffers = new ConcurrentHashMap<>();
-    private final int _factor;
+    private final Function<Integer, Bucket> _newBucket;
-    private final int _maxQueueLength;
 
     /**
      * Creates a new MappedByteBufferPool with a default configuration.
@@ -60,20 +59,46 @@ public class MappedByteBufferPool implements ByteBufferPool
     }
 
     /**
-     * Creates a new MappedByteBufferPool with the given capacity factor and max queue length.
+     * Creates a new MappedByteBufferPool with the given configuration.
      *
      * @param factor the capacity factor
      * @param maxQueueLength the maximum ByteBuffer queue length
      */
     public MappedByteBufferPool(int factor, int maxQueueLength)
     {
-        _factor = factor <= 0 ? 1024 : factor;
+        this(factor, maxQueueLength, null);
-        _maxQueueLength = maxQueueLength;
+    }
+
+    /**
+     * Creates a new MappedByteBufferPool with the given configuration.
+     *
+     * @param factor the capacity factor
+     * @param maxQueueLength the maximum ByteBuffer queue length
+     * @param newBucket the function that creates a Bucket
+     */
+    public MappedByteBufferPool(int factor, int maxQueueLength, Function<Integer, Bucket> newBucket)
+    {
+        this(factor, maxQueueLength, newBucket, -1, -1);
+    }
+
+    /**
+     * Creates a new MappedByteBufferPool with the given configuration.
+     *
+     * @param factor the capacity factor
+     * @param maxQueueLength the maximum ByteBuffer queue length
+     * @param newBucket the function that creates a Bucket
+     * @param maxHeapMemory the max heap memory in bytes
+     * @param maxDirectMemory the max direct memory in bytes
+     */
+    public MappedByteBufferPool(int factor, int maxQueueLength, Function<Integer, Bucket> newBucket, long maxHeapMemory, long maxDirectMemory)
+    {
+        super(factor, maxQueueLength, maxHeapMemory, maxDirectMemory);
+        _newBucket = newBucket != null ? newBucket : this::newBucket;
     }
 
     private Bucket newBucket(int key)
     {
-        return new Bucket(this, key * _factor, _maxQueueLength);
+        return new Bucket(this, key * getCapacityFactor(), getMaxQueueLength());
     }
 
     @Override
@@ -83,8 +108,10 @@ public class MappedByteBufferPool implements ByteBufferPool
         ConcurrentMap<Integer, Bucket> buffers = bucketsFor(direct);
         Bucket bucket = buffers.get(b);
         if (bucket == null)
-            return newByteBuffer(b * _factor, direct);
+            return newByteBuffer(b * getCapacityFactor(), direct);
-        return bucket.acquire(direct);
+        ByteBuffer buffer = bucket.acquire(direct);
+        decrementMemory(buffer);
+        return buffer;
     }
 
     @Override
@@ -93,29 +120,33 @@ public class MappedByteBufferPool implements ByteBufferPool
         if (buffer == null)
             return; // nothing to do
 
-        // validate that this buffer is from this pool
+        int capacity = buffer.capacity();
-        assert ((buffer.capacity() % _factor) == 0);
+        // Validate that this buffer is from this pool.
+        assert ((capacity % getCapacityFactor()) == 0);
 
-        int b = bucketFor(buffer.capacity());
+        int b = bucketFor(capacity);
         ConcurrentMap<Integer, Bucket> buckets = bucketsFor(buffer.isDirect());
+        Bucket bucket = buckets.computeIfAbsent(b, _newBucket);
 
-        Bucket bucket = buckets.computeIfAbsent(b, this::newBucket);
+        if (incrementMemory(buffer))
-        bucket.release(buffer);
+            bucket.release(buffer);
     }
 
-    @ManagedOperation(value = "Clears this ByteBufferPool", impact = "ACTION")
+    @Override
     public void clear()
     {
-        directBuffers.values().forEach(Bucket::clear);
+        super.clear();
-        directBuffers.clear();
+        _directBuffers.values().forEach(Bucket::clear);
-        heapBuffers.values().forEach(Bucket::clear);
+        _directBuffers.clear();
-        heapBuffers.clear();
+        _heapBuffers.values().forEach(Bucket::clear);
+        _heapBuffers.clear();
     }
 
     private int bucketFor(int size)
     {
-        int bucket = size / _factor;
+        int factor = getCapacityFactor();
-        if (size % _factor > 0)
+        int bucket = size / factor;
+        if (bucket * factor != size)
             ++bucket;
         return bucket;
     }
@@ -123,7 +154,7 @@ public class MappedByteBufferPool implements ByteBufferPool
     // Package local for testing
     ConcurrentMap<Integer, Bucket> bucketsFor(boolean direct)
     {
-        return direct ? directBuffers : heapBuffers;
+        return direct ? _directBuffers : _heapBuffers;
     }
 
     public static class Tagged extends MappedByteBufferPool

jetty-io/src/test/java/org/eclipse/jetty/io/ArrayByteBufferPoolTest.java

@@ -20,12 +20,17 @@ package org.eclipse.jetty.io;
 
 import java.nio.ByteBuffer;
 import java.util.Arrays;
+import java.util.List;
+import java.util.Objects;
+import java.util.stream.Collectors;
 
 import org.eclipse.jetty.io.ByteBufferPool.Bucket;
 import org.junit.jupiter.api.Test;
 
 import static org.hamcrest.MatcherAssert.assertThat;
 import static org.hamcrest.Matchers.greaterThanOrEqualTo;
+import static org.hamcrest.Matchers.lessThan;
+import static org.hamcrest.Matchers.lessThanOrEqualTo;
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertNotSame;
 import static org.junit.jupiter.api.Assertions.assertSame;
@@ -46,12 +51,18 @@ public class ArrayByteBufferPoolTest
             assertTrue(buffer.isDirect());
             assertEquals(size, buffer.capacity());
             for (ByteBufferPool.Bucket bucket : buckets)
-                assertTrue(bucket.isEmpty());
+            {
+                if (bucket != null)
+                    assertTrue(bucket.isEmpty());
+            }
 
             bufferPool.release(buffer);
 
             for (ByteBufferPool.Bucket bucket : buckets)
-                assertTrue(bucket.isEmpty());
+            {
+                if (bucket != null)
+                    assertTrue(bucket.isEmpty());
+            }
         }
     }
 
@@ -69,15 +80,17 @@ public class ArrayByteBufferPoolTest
             assertTrue(buffer.isDirect());
             assertThat(buffer.capacity(), greaterThanOrEqualTo(size));
             for (ByteBufferPool.Bucket bucket : buckets)
-                assertTrue(bucket.isEmpty());
+            {
+                if (bucket != null)
+                    assertTrue(bucket.isEmpty());
+            }
 
             bufferPool.release(buffer);
 
-            int pooled = 0;
+            int pooled = Arrays.stream(buckets)
-            for (ByteBufferPool.Bucket bucket : buckets)
+                    .filter(Objects::nonNull)
-            {
+                    .mapToInt(Bucket::size)
-                pooled += bucket.size();
+                    .sum();
-            }
             assertEquals(size <= 1000, 1 == pooled);
         }
     }
@@ -96,20 +109,17 @@ public class ArrayByteBufferPoolTest
             assertTrue(buffer.isDirect());
             assertThat(buffer.capacity(), greaterThanOrEqualTo(size));
             for (ByteBufferPool.Bucket bucket : buckets)
-                assertTrue(bucket.isEmpty());
+            {
+                if (bucket != null)
+                    assertTrue(bucket.isEmpty());
+            }
 
             bufferPool.release(buffer);
 
-            int pooled = 0;
+            int pooled = Arrays.stream(buckets)
-            for (ByteBufferPool.Bucket bucket : buckets)
+                    .filter(Objects::nonNull)
-            {
+                    .mapToInt(Bucket::size)
-                if (!bucket.isEmpty())
+                    .sum();
-                {
-                    pooled += bucket.size();
-                    // TODO assertThat(bucket._bufferSize,greaterThanOrEqualTo(size));
-                    // TODO assertThat(bucket._bufferSize,Matchers.lessThan(size+100));
-                }
-            }
             assertEquals(1, pooled);
         }
     }
@@ -130,16 +140,10 @@ public class ArrayByteBufferPoolTest
             ByteBuffer buffer3 = bufferPool.acquire(size, false);
             bufferPool.release(buffer3);
 
-            int pooled = 0;
+            int pooled = Arrays.stream(buckets)
-            for (ByteBufferPool.Bucket bucket : buckets)
+                    .filter(Objects::nonNull)
-            {
+                    .mapToInt(Bucket::size)
-                if (!bucket.isEmpty())
+                    .sum();
-                {
-                    pooled += bucket.size();
-                    // TODO assertThat(bucket._bufferSize,greaterThanOrEqualTo(size));
-                    // TODO assertThat(bucket._bufferSize,Matchers.lessThan(size+100));
-                }
-            }
             assertEquals(1, pooled);
 
             assertSame(buffer1, buffer2);
@@ -157,10 +161,16 @@ public class ArrayByteBufferPoolTest
         ByteBuffer buffer3 = bufferPool.acquire(512, false);
 
         Bucket[] buckets = bufferPool.bucketsFor(false);
-        Arrays.asList(buckets).forEach(b -> assertEquals(0, b.size()));
+        Arrays.stream(buckets)
+                .filter(Objects::nonNull)
+                .forEach(b -> assertEquals(0, b.size()));
 
         bufferPool.release(buffer1);
-        Bucket bucket = Arrays.stream(buckets).filter(b -> b.size() > 0).findFirst().get();
+        Bucket bucket = Arrays.stream(buckets)
+                .filter(Objects::nonNull)
+                .filter(b -> b.size() > 0)
+                .findFirst()
+                .orElseThrow(AssertionError::new);
         assertEquals(1, bucket.size());
 
         bufferPool.release(buffer2);
@@ -169,4 +179,41 @@ public class ArrayByteBufferPoolTest
         bufferPool.release(buffer3);
         assertEquals(2, bucket.size());
     }
+
+    @Test
+    public void testMaxMemory()
+    {
+        int factor = 1024;
+        int maxMemory = 10 * 1024;
+        ArrayByteBufferPool bufferPool = new ArrayByteBufferPool(-1, factor, -1, -1, -1, maxMemory);
+
+        int capacity = 3 * 1024;
+        ByteBuffer[] buffers = new ByteBuffer[maxMemory / capacity + 1];
+        for (int i = 0; i < buffers.length; ++i)
+            buffers[i] = bufferPool.acquire(capacity, true);
+
+        // Return all the buffers, but only some is retained by the pool.
+        for (ByteBuffer buffer : buffers)
+            bufferPool.release(buffer);
+
+        List<Bucket> directBuckets = Arrays.stream(bufferPool.bucketsFor(true))
+                .filter(Objects::nonNull)
+                .filter(b -> !b.isEmpty())
+                .collect(Collectors.toList());
+        assertEquals(1, directBuckets.size());
+
+        Bucket bucket = directBuckets.get(0);
+        assertEquals(buffers.length - 1, bucket.size());
+
+        long memory1 = bufferPool.getMemory(true);
+        assertThat(memory1, lessThanOrEqualTo((long)maxMemory));
+
+        ByteBuffer buffer = bufferPool.acquire(capacity, true);
+        long memory2 = bufferPool.getMemory(true);
+        assertThat(memory2, lessThan(memory1));
+
+        bufferPool.release(buffer);
+        long memory3 = bufferPool.getMemory(true);
+        assertEquals(memory1, memory3);
+    }
 }

jetty-io/src/test/java/org/eclipse/jetty/io/MappedByteBufferPoolTest.java

@@ -29,6 +29,8 @@ import org.junit.jupiter.api.Test;
 import static org.hamcrest.MatcherAssert.assertThat;
 import static org.hamcrest.Matchers.containsString;
 import static org.hamcrest.Matchers.greaterThanOrEqualTo;
+import static org.hamcrest.Matchers.lessThan;
+import static org.hamcrest.Matchers.lessThanOrEqualTo;
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertSame;
 import static org.junit.jupiter.api.Assertions.assertTrue;
@@ -156,4 +158,37 @@ public class MappedByteBufferPoolTest
         bufferPool.release(buffer3);
         assertEquals(2, bucket.size());
     }
+
+    @Test
+    public void testMaxMemory()
+    {
+        int factor = 1024;
+        int maxMemory = 10 * 1024;
+        MappedByteBufferPool bufferPool = new MappedByteBufferPool(factor, -1, null, -1, maxMemory);
+
+        int capacity = 3 * 1024;
+        ByteBuffer[] buffers = new ByteBuffer[maxMemory / capacity + 1];
+        for (int i = 0; i < buffers.length; ++i)
+            buffers[i] = bufferPool.acquire(capacity, true);
+
+        // Return all the buffers, but only some is retained by the pool.
+        for (ByteBuffer buffer : buffers)
+            bufferPool.release(buffer);
+
+        ConcurrentMap<Integer, Bucket> directMap = bufferPool.bucketsFor(true);
+        assertEquals(1, directMap.size());
+        Bucket bucket = directMap.values().iterator().next();
+        assertEquals(buffers.length - 1, bucket.size());
+
+        long memory1 = bufferPool.getMemory(true);
+        assertThat(memory1, lessThanOrEqualTo((long)maxMemory));
+
+        ByteBuffer buffer = bufferPool.acquire(capacity, true);
+        long memory2 = bufferPool.getMemory(true);
+        assertThat(memory2, lessThan(memory1));
+
+        bufferPool.release(buffer);
+        long memory3 = bufferPool.getMemory(true);
+        assertEquals(memory1, memory3);
+    }
 }