Try reuse existing Netty pooled allocator singleton (Fixes #5168)

src/main/java/io/vertx/core/buffer/impl/VertxByteBufAllocator.java

@@ -22,11 +22,13 @@ public abstract class VertxByteBufAllocator extends AbstractByteBufAllocator {
   /**
    * Vert.x pooled allocator.
    */
-  public static final ByteBufAllocator POOLED_ALLOCATOR = new PooledByteBufAllocator(true);
+  public static final ByteBufAllocator POOLED_ALLOCATOR = PooledByteBufAllocator.defaultPreferDirect() ?
+    PooledByteBufAllocator.DEFAULT : new PooledByteBufAllocator(true);
   /**
    * Vert.x shared unpooled allocator.
    */
-  public static final ByteBufAllocator UNPOOLED_ALLOCATOR = new UnpooledByteBufAllocator(false);
+  public static final ByteBufAllocator UNPOOLED_ALLOCATOR = PooledByteBufAllocator.defaultPreferDirect() ?
+    UnpooledByteBufAllocator.DEFAULT : new UnpooledByteBufAllocator(false);
 
   private static final VertxByteBufAllocator UNSAFE_IMPL = new VertxByteBufAllocator() {
     @Override
@@ -42,6 +44,10 @@ protected ByteBuf newHeapBuffer(int initialCapacity, int maxCapacity) {
     }
   };
 
+  /**
+   * Vert.x shared unpooled allocator.<br>
+   * Differently from {@link #POOLED_ALLOCATOR}, its heap buffers are not reference counted.
+   */
   public static final VertxByteBufAllocator DEFAULT = PlatformDependent.hasUnsafe() ? UNSAFE_IMPL : IMPL;
 
   @Override

src/main/java/io/vertx/core/net/impl/TCPServerBase.java

@@ -26,6 +26,7 @@
 import io.vertx.core.Handler;
 import io.vertx.core.Promise;
 import io.vertx.core.buffer.impl.PartialPooledByteBufAllocator;
+import io.vertx.core.buffer.impl.VertxByteBufAllocator;
 import io.vertx.core.impl.ContextInternal;
 import io.vertx.core.impl.future.PromiseInternal;
 import io.vertx.core.impl.VertxInternal;
@@ -245,7 +246,7 @@ private synchronized Future<Channel> listen(SocketAddress localAddress, ContextI
             if (options.isSsl()) {
               bootstrap.childOption(ChannelOption.ALLOCATOR, PartialPooledByteBufAllocator.INSTANCE);
             } else {
-              bootstrap.childOption(ChannelOption.ALLOCATOR, PooledByteBufAllocator.DEFAULT);
+              bootstrap.childOption(ChannelOption.ALLOCATOR, VertxByteBufAllocator.POOLED_ALLOCATOR);
             }
 
             bootstrap.childHandler(channelBalancer);

src/test/java/io/vertx/core/buffer/impl/VertxByteBufAllocatorTest.java

@@ -0,0 +1,31 @@
+/*
+ * Copyright (c) 2011-2024 Contributors to the Eclipse Foundation
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Public License 2.0 which is available at
+ * http://www.eclipse.org/legal/epl-2.0, or the Apache License, Version 2.0
+ * which is available at https://www.apache.org/licenses/LICENSE-2.0.
+ *
+ * SPDX-License-Identifier: EPL-2.0 OR Apache-2.0
+ */
+
+package io.vertx.core.buffer.impl;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+import io.netty.buffer.ByteBufAllocator;
+import io.netty.buffer.PooledByteBufAllocator;
+import io.netty.buffer.UnpooledByteBufAllocator;
+
+public class VertxByteBufAllocatorTest {
+
+  @Test
+  public void shouldReuseTheExistingNettyAllocators() {
+    Assert.assertTrue(PooledByteBufAllocator.defaultPreferDirect());
+    Assert.assertSame(PooledByteBufAllocator.DEFAULT, VertxByteBufAllocator.POOLED_ALLOCATOR);
+    Assert.assertSame(ByteBufAllocator.DEFAULT, VertxByteBufAllocator.POOLED_ALLOCATOR);
+    Assert.assertSame(UnpooledByteBufAllocator.DEFAULT, VertxByteBufAllocator.UNPOOLED_ALLOCATOR);
+  }
+
+}