ARROW-1760: [Java] Add Apache Mnemonic (incubating) as alternative backed allocator

.gitignore

@@ -29,3 +29,4 @@ cpp/.idea/
 python/.eggs/
 .vscode
 .idea/
+

java/.gitignore

@@ -20,4 +20,6 @@ CMakeFiles
 Makefile
 cmake_install.cmake
 install_manifest.txt
+*.dat
 ?/
+

java/memory/pom.xml

@@ -40,6 +40,10 @@
       <groupId>org.slf4j</groupId>
       <artifactId>slf4j-api</artifactId>
     </dependency>
+    <dependency>
+      <groupId>org.apache.mnemonic</groupId>
+      <artifactId>mnemonic-core</artifactId>
+    </dependency>
   </dependencies>
 
   <build>

java/memory/src/main/java/io/netty/buffer/MnemonicUnpooledByteBufAllocator.java

@@ -0,0 +1,72 @@
+/*
+ * Copyright 2012 The Netty Project
+ *
+ * The Netty Project 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 io.netty.buffer;
+
+import io.netty.util.internal.PlatformDependent;
+
+import org.apache.mnemonic.CommonAllocator;
+
+/**
+ * Simplistic {@link ByteBufAllocator} implementation that does not pool anything.
+ */
+public final class MnemonicUnpooledByteBufAllocator<A extends CommonAllocator<A>> extends AbstractByteBufAllocator {
+
+    private A mcalloc;
+
+    /**
+     * Default instance
+     */
+    //        public static final UnpooledByteBufAllocator DEFAULT =
+    //      new UnpooledByteBufAllocator(PlatformDependent.directBufferPreferred());
+
+    /**
+     * Create a new instance
+     *
+     * @param preferDirect {@code true} if {@link #buffer(int)} should try to allocate a direct buffer rather than
+     *                     a heap buffer
+     */
+    public MnemonicUnpooledByteBufAllocator(boolean preferDirect, A mcallocator) {
+        super(preferDirect);
+	this.mcalloc = mcallocator;
+    }
+
+    public A getAllocator() {
+	return this.mcalloc;
+    }
+
+        @Override
+        protected ByteBuf newHeapBuffer(int initialCapacity, int maxCapacity) {
+            return new UnpooledHeapByteBuf(this, initialCapacity, maxCapacity);
+        }
+
+        @Override
+        protected ByteBuf newDirectBuffer(int initialCapacity, int maxCapacity) {
+	    assert null != this.mcalloc;
+            ByteBuf buf;
+            if (PlatformDependent.hasUnsafe()) {
+                buf = new MnemonicUnpooledUnsafeDirectByteBuf<A>(this, initialCapacity, maxCapacity);
+            } else {
+                buf = new MnemonicUnpooledDirectByteBuf<A>(this, initialCapacity, maxCapacity);
+            }
+
+            return toLeakAwareBuffer(buf);
+        }
+
+        @Override
+        public boolean isDirectBufferPooled() {
+            return false;
+        }
+}