Github user dain commented on a diff in the pull request:
https://github.com/apache/zookeeper/pull/669#discussion_r225332620
--- Diff:
zookeeper-common/src/test/java/org/apache/zookeeper/common/TestByteBufAllocator.java
---
@@ -0,0 +1,145 @@
+/*
+ * 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.zookeeper.common;
+
+import io.netty.buffer.ByteBuf;
+import io.netty.buffer.CompositeByteBuf;
+import io.netty.buffer.PooledByteBufAllocator;
+import io.netty.util.ResourceLeakDetector;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.concurrent.atomic.AtomicReference;
+
+/**
+ * This is a custom ByteBufAllocator that tracks outstanding allocations
and
+ * crashes the program if any of them are leaked.
+ *
+ * Never use this class in production, it will cause your server to run out
+ * of memory! This is because it holds strong references to all allocated
+ * buffers and doesn't release them until checkForLeaks() is called at the
+ * end of a unit test.
+ *
+ * Note: the original code was copied from
https://github.com/airlift/drift,
+ * with the permission and encouragement of airlift's author (dain).
Airlift
+ * uses the same apache 2.0 license as Zookeeper so this should be ok.
+ *
+ * However, the code was modified to take advantage of Netty's built-in
+ * leak tracking and make a best effort to print details about buffer
leaks.
+ */
+public class TestByteBufAllocator extends PooledByteBufAllocator {
+private static AtomicReference INSTANCE =
+new AtomicReference<>(null);
+
+/**
+ * Get the singleton testing allocator.
+ * @return the singleton allocator, creating it if one does not exist.
+ */
+public static TestByteBufAllocator getInstance() {
+TestByteBufAllocator result = INSTANCE.get();
+if (result == null) {
+// Note: the leak detector level never gets reset after this,
+// but that's probably ok since this is only used by test code.
+
ResourceLeakDetector.setLevel(ResourceLeakDetector.Level.PARANOID);
+INSTANCE.compareAndSet(null, new TestByteBufAllocator());
+result = INSTANCE.get();
+}
+return result;
+}
+
+/**
+ * Destroys the singleton testing allocator and throws an error if any
of the
+ * buffers allocated by it have been leaked. Attempts to print leak
details to
+ * standard error before throwing, by using netty's built-in leak
tracking.
+ * Note that this might not always work, since it only triggers when a
buffer
+ * is garbage-collected and calling System.gc() does not guarantee
that a buffer
+ * will actually be GC'ed.
+ *
+ * This should be called at the end of a unit test's tearDown() method.
+ */
+public static void checkForLeaks() {
+TestByteBufAllocator result = INSTANCE.getAndSet(null);
+if (result != null) {
+result.checkInstanceForLeaks();
+}
+
+}
+
+private final List trackedBuffers = new ArrayList<>();
+
+public TestByteBufAllocator()
+{
+super(false);
+}
+
+@Override
+protected ByteBuf newHeapBuffer(int initialCapacity, int maxCapacity)
+{
+return track(super.newHeapBuffer(initialCapacity, maxCapacity));
+}
+
+@Override
+protected ByteBuf newDirectBuffer(int initialCapacity, int maxCapacity)
+{
+return track(super.newDirectBuffer(initialCapacity, maxCapacity));
+}
+
+@Override
+public CompositeByteBuf compositeHeapBuffer(int maxNumComponents)
+{
+return track(super.compositeHeapBuffer(maxNumComponents));
+}
+
+@Override
+public CompositeByteBuf compositeD
