Merge pull request #68 from netty/modules

Split the repo into multiple modules and make building with Java 11 possible

.github/workflows/ci-workflow.yml

@@ -1,4 +1,4 @@
-name: CI Build
+name: Build
 
 # Controls when the action will run. 
 on:
@@ -13,14 +13,9 @@ on:
   # Allows you to run this workflow manually from the Actions tab
   workflow_dispatch:
 
-# A workflow run is made up of one or more jobs that can run sequentially or in parallel
 jobs:
-  # This workflow contains a single job called "build"
-  build:
-    # The type of runner that the job will run on
+  java17:
     runs-on: ubuntu-latest
-
-    # Steps represent a sequence of tasks that will be executed as part of the job
     steps:
       # http://man7.org/linux/man-pages/man1/date.1.html
       - name: Create Cache Key
@@ -50,7 +45,7 @@ jobs:
           github_token: ${{ secrets.GITHUB_TOKEN }}
           report_paths: '**/target/surefire-reports/TEST-*.xml'
           commit: ${{ github.event.workflow_run.head_commit.id }}
-          check_name: Build test reports
+          check_name: java17 test reports
       - name: Upload build artefacts
         uses: actions/upload-artifact@v2
         if: ${{ failure() }}
@@ -60,3 +55,34 @@ jobs:
       # Make room for the docker layer caching to package up layers
       - name: Cleanup
         run: rm -fr *
+  java11:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - name: Set up Java 11
+        uses: actions/setup-java@v2
+        with:
+          distribution: 'adopt' # See 'Supported distributions' for available options
+          java-version: '11'
+      - uses: actions/cache@v2
+        with:
+          path: ~/.m2/repository
+          key: ${{ runner.os }}-maven-${{ hashFiles('**/pom.xml') }}
+          restore-keys: |
+            ${{ runner.os }}-maven-
+      - name: Maven build
+        run: mvn verify -B -C -T1C -fae
+      - name: Publish Test Report
+        uses: scacap/action-surefire-report@v1.0.9
+        if: ${{ always() }}
+        with:
+          github_token: ${{ secrets.GITHUB_TOKEN }}
+          report_paths: '**/target/surefire-reports/TEST-*.xml'
+          commit: ${{ github.event.workflow_run.head_commit.id }}
+          check_name: java11 test reports
+      - name: Upload build artefacts
+        uses: actions/upload-artifact@v2
+        if: ${{ failure() }}
+        with:
+          name: artifacts
+          path: target/

Dockerfile

@@ -29,8 +29,12 @@ RUN git clone --depth 1 -b master https://github.com/netty/netty.git netty \
     && rm -fr netty
 
 # Prepare our own build
+RUN mkdir buffer-api && mkdir buffer-memseg && mkdir buffer-tests
 COPY pom.xml pom.xml
-RUN mvn dependency:go-offline surefire:test checkstyle:check -ntp
+COPY buffer-api/pom.xml buffer-api/pom.xml
+COPY buffer-memseg/pom.xml buffer-memseg/pom.xml
+COPY buffer-tests/pom.xml buffer-tests/pom.xml
+RUN mvn install dependency:go-offline surefire:test checkstyle:check -ntp
 
 # Copy over the project code and run our build
 COPY . .

Makefile

@@ -25,6 +25,9 @@ build: image
 	docker start -a build-container || (docker cp build-container:/home/build target/container-output && false)
 	docker wait build-container || (docker cp build-container:/home/build target/container-output && false)
 	docker cp build-container:/home/build/target .
+	docker cp build-container:/home/build/buffer-api/target .
+	docker cp build-container:/home/build/buffer-memseg/target .
+	docker cp build-container:/home/build/buffer-tests/target .
 	docker rm build-container
 
 rebuild: clean clean-layer-cache build

README.adoc

@@ -6,9 +6,9 @@ See the xref:RATIONALE.adoc[RATIONALE] document for more background.
 
 == Building and Testing
 
-Short version: just run `make`.
+Short version: just run `make` if you want to build on Java 17, otherwise run `mvn install` if you want to build with Java 11, and without support for the `jdk.incubator.foreign` APIs.
 
-The project currently relies on snapshot versions of the https://github.com/openjdk/panama-foreign[Panama Foreign] fork of OpenJDK.
+The project (specifically, the `buffer-memseg` module) currently relies on snapshot versions of the https://github.com/openjdk/panama-foreign[Panama Foreign] fork of OpenJDK.
 This allows us to test out the most recent version of the `jdk.incubator.foreign` APIs, but also make building, and local development more involved.
 To simplify things, we have a Docker based build, controlled via a Makefile with the following commands:
 

buffer-api/pom.xml

@@ -0,0 +1,43 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+  ~ Copyright 2021 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:
+  ~
+  ~   https://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.
+  -->
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+
+    <parent>
+        <groupId>io.netty.incubator</groupId>
+        <artifactId>netty-incubator-buffer-parent</artifactId>
+        <version>0.0.1.Final-SNAPSHOT</version>
+    </parent>
+
+    <artifactId>netty-incubator-buffer-api</artifactId>
+    <version>0.0.1.Final-SNAPSHOT</version>
+    <name>Netty/Incubator/Buffer</name>
+    <packaging>jar</packaging>
+
+    <dependencies>
+        <dependency>
+            <groupId>io.netty</groupId>
+            <artifactId>netty-common</artifactId>
+        </dependency>
+        <dependency>
+            <groupId>io.netty</groupId>
+            <artifactId>netty-buffer</artifactId>
+        </dependency>
+    </dependencies>
+</project>

buffer-api/src/main/java/io/netty/buffer/api/BufferHolder.java

@@ -15,10 +15,11 @@
  */
 package io.netty.buffer.api;
 
+import io.netty.buffer.api.internal.Statics;
+
 import java.lang.invoke.VarHandle;
 import java.util.Objects;
 
-import static io.netty.buffer.api.internal.Statics.findVarHandle;
 import static java.lang.invoke.MethodHandles.lookup;
 
 /**
@@ -36,7 +37,7 @@ import static java.lang.invoke.MethodHandles.lookup;
  * @param <T> The concrete {@link BufferHolder} type.
  */
 public abstract class BufferHolder<T extends BufferHolder<T>> implements Rc<T> {
-    private static final VarHandle BUF = findVarHandle(lookup(), BufferHolder.class, "buf", Buffer.class);
+    private static final VarHandle BUF = Statics.findVarHandle(lookup(), BufferHolder.class, "buf", Buffer.class);
     private Buffer buf;
 
     /**

buffer-api/src/main/java/io/netty/buffer/api/LifecycleTracer.java

@@ -15,7 +15,6 @@
  */
 package io.netty.buffer.api;
 
-import java.io.Serial;
 import java.util.ArrayDeque;
 import java.util.Set;
 import java.util.function.Function;
@@ -176,7 +175,6 @@ abstract class LifecycleTracer {
     }
 
     private static final class Traceback extends Throwable {
-        @Serial
         private static final long serialVersionUID = 941453986194634605L;
 
         Traceback(String message) {

buffer-api/src/main/java/io/netty/buffer/api/MemoryManagersOverride.java

@@ -15,7 +15,7 @@
  */
 package io.netty.buffer.api;
 
-import io.netty.buffer.api.memseg.SegmentMemoryManagers;
+import io.netty.buffer.api.bytebuffer.ByteBufferMemoryManagers;
 
 import java.util.Collections;
 import java.util.IdentityHashMap;
@@ -24,7 +24,7 @@ import java.util.concurrent.atomic.AtomicInteger;
 import java.util.function.Supplier;
 
 final class MemoryManagersOverride {
-    private static final MemoryManagers DEFAULT = new SegmentMemoryManagers();
+    private static final MemoryManagers DEFAULT = new ByteBufferMemoryManagers();
     private static final AtomicInteger OVERRIDES_AVAILABLE = new AtomicInteger();
     private static final Map<Thread, MemoryManagers> OVERRIDES = Collections.synchronizedMap(new IdentityHashMap<>());
 

buffer-api/src/main/java/io/netty/buffer/api/TransferSend.java

@@ -15,13 +15,14 @@
  */
 package io.netty.buffer.api;
 
+import io.netty.buffer.api.internal.Statics;
+
 import java.lang.invoke.VarHandle;
 
-import static io.netty.buffer.api.internal.Statics.findVarHandle;
 import static java.lang.invoke.MethodHandles.lookup;
 
 class TransferSend<I extends Rc<I>, T extends Rc<I>> implements Send<I> {
-    private static final VarHandle RECEIVED = findVarHandle(lookup(), TransferSend.class, "received", boolean.class);
+    private static final VarHandle RECEIVED = Statics.findVarHandle(lookup(), TransferSend.class, "received", boolean.class);
     private final Owned<T> outgoing;
     private final Drop<T> drop;
     private final Class<?> concreteType;

buffer-api/src/main/java/io/netty/buffer/api/adaptor/ByteBufAdaptor.java

@@ -22,8 +22,9 @@ import io.netty.buffer.ByteBufUtil;
 import io.netty.buffer.DuplicatedByteBuf;
 import io.netty.buffer.SlicedByteBuf;
 import io.netty.buffer.Unpooled;
-import io.netty.buffer.api.Buffer;
 import io.netty.buffer.api.BufferAllocator;
+import io.netty.buffer.api.internal.Statics;
+import io.netty.buffer.api.Buffer;
 import io.netty.buffer.api.RcSupport;
 import io.netty.util.ByteProcessor;
 import io.netty.util.IllegalReferenceCountException;
@@ -1514,7 +1515,7 @@ public final class ByteBufAdaptor extends ByteBuf {
             });
             ByteBuffer buffer = bufRef.get();
             if (index != readerIndex() || length != readableBytes()) {
-                buffer = buffer.slice(index - readerIndex(), length);
+                buffer = Statics.bbslice(buffer, index - readerIndex(), length);
             }
             return buffer;
         } else if (writerIndex() <= index && length <= writableBytes()) {
@@ -1530,7 +1531,7 @@ public final class ByteBufAdaptor extends ByteBuf {
             });
             ByteBuffer buffer = bufRef.get();
             if (index != writerIndex() || length != writableBytes()) {
-                buffer = buffer.slice(index - writerIndex(), length);
+                buffer = Statics.bbslice(buffer, index - writerIndex(), length);
             }
             return buffer;
         } else {

buffer-api/src/main/java/io/netty/buffer/api/bytebuffer/ByteBufferMemoryManager.java

@@ -25,6 +25,7 @@ import java.lang.ref.Cleaner;
 import java.nio.ByteBuffer;
 import java.nio.ByteOrder;
 
+import static io.netty.buffer.api.internal.Statics.bbslice;
 import static io.netty.buffer.api.internal.Statics.convert;
 
 public class ByteBufferMemoryManager implements MemoryManager {
@@ -84,6 +85,6 @@ public class ByteBufferMemoryManager implements MemoryManager {
     @Override
     public Object sliceMemory(Object memory, int offset, int length) {
         var buffer = (ByteBuffer) memory;
-        return buffer.slice(offset, length);
+        return bbslice(buffer, offset, length);
     }
 }

buffer-api/src/main/java/io/netty/buffer/api/bytebuffer/NioBuffer.java

@@ -34,6 +34,8 @@ import java.nio.ByteBuffer;
 import java.nio.ByteOrder;
 import java.nio.ReadOnlyBufferException;
 
+import static io.netty.buffer.api.internal.Statics.bbput;
+import static io.netty.buffer.api.internal.Statics.bbslice;
 import static io.netty.buffer.api.internal.Statics.bufferIsClosed;
 import static io.netty.buffer.api.internal.Statics.bufferIsReadOnly;
 
@@ -64,7 +66,7 @@ class NioBuffer extends RcSupport<Buffer, NioBuffer> implements Buffer, Readable
         super(new MakeInaccisbleOnDrop(new ArcDrop<>(ArcDrop.acquire(parent.unsafeGetDrop()))));
         control = parent.control;
         base = parent.base;
-        rmem = parent.rmem.slice(0, parent.rmem.capacity()); // Need to slice to get independent byte orders.
+        rmem = bbslice(parent.rmem, 0, parent.rmem.capacity()); // Need to slice to get independent byte orders.
         assert parent.wmem == CLOSED_BUFFER;
         wmem = CLOSED_BUFFER;
         roff = parent.roff;
@@ -193,7 +195,7 @@ class NioBuffer extends RcSupport<Buffer, NioBuffer> implements Buffer, Readable
         if (!isAccessible()) {
             throw new IllegalStateException("This buffer is closed: " + this + '.');
         }
-        ByteBuffer slice = rmem.slice(offset, length);
+        ByteBuffer slice = bbslice(rmem, offset, length);
         ArcDrop<NioBuffer> drop = (ArcDrop<NioBuffer>) unsafeGetDrop();
         drop.increment();
         Buffer sliceBuffer = new NioBuffer(base, slice, control, drop)
@@ -226,7 +228,7 @@ class NioBuffer extends RcSupport<Buffer, NioBuffer> implements Buffer, Readable
                     "srcPos = " + srcPos + ", length = " + length + '.');
         }
         dest = dest.duplicate().clear();
-        dest.put(destPos, rmem, srcPos, length);
+        bbput(dest, destPos, rmem, srcPos, length);
     }
 
     @Override
@@ -453,12 +455,13 @@ class NioBuffer extends RcSupport<Buffer, NioBuffer> implements Buffer, Readable
         }
         var drop = (ArcDrop<NioBuffer>) unsafeGetDrop();
         unsafeSetDrop(new ArcDrop<>(drop));
-        var splitByteBuffer = rmem.slice(0, splitOffset);
+        var splitByteBuffer = bbslice(rmem, 0, splitOffset);
         // TODO maybe incrementing the existing ArcDrop is enough; maybe we don't need to wrap it in another ArcDrop.
         var splitBuffer = new NioBuffer(base, splitByteBuffer, control, new ArcDrop<>(drop.increment()));
         splitBuffer.woff = Math.min(woff, splitOffset);
         splitBuffer.roff = Math.min(roff, splitOffset);
-        splitBuffer.order(order());
+        ByteOrder order = order();
+        splitBuffer.order(order);
         boolean readOnly = readOnly();
         if (readOnly) {
             splitBuffer.makeReadOnly();
@@ -466,12 +469,13 @@ class NioBuffer extends RcSupport<Buffer, NioBuffer> implements Buffer, Readable
         // Note that split, unlike slice, does not deconstify, because data changes in either buffer are not visible
         // in the other. The split buffers can later deconstify independently if needed.
         splitBuffer.constBuffer = constBuffer;
-        rmem = rmem.slice(splitOffset, rmem.capacity() - splitOffset);
+        rmem = bbslice(rmem, splitOffset, rmem.capacity() - splitOffset);
         if (!readOnly) {
             wmem = rmem;
         }
         woff = Math.max(woff, splitOffset) - splitOffset;
         roff = Math.max(roff, splitOffset) - splitOffset;
+        order(order);
         return splitBuffer;
     }
 
@@ -534,7 +538,7 @@ class NioBuffer extends RcSupport<Buffer, NioBuffer> implements Buffer, Readable
 
     @Override
     public ByteBuffer readableBuffer() {
-        return rmem.asReadOnlyBuffer().slice(readerOffset(), readableBytes()).order(order());
+        return bbslice(rmem.asReadOnlyBuffer(), readerOffset(), readableBytes()).order(order());
     }
 
     @Override
@@ -564,7 +568,7 @@ class NioBuffer extends RcSupport<Buffer, NioBuffer> implements Buffer, Readable
 
     @Override
     public ByteBuffer writableBuffer() {
-        return wmem.slice(writerOffset(), writableBytes()).order(order());
+        return bbslice(wmem, writerOffset(), writableBytes()).order(order());
     }
     // </editor-fold>
 

buffer-api/src/main/java/io/netty/buffer/api/internal/CleanerDrop.java

@@ -17,7 +17,6 @@ package io.netty.buffer.api.internal;
 
 import io.netty.buffer.api.Drop;
 
-import java.io.Serial;
 import java.lang.ref.Cleaner;
 import java.util.concurrent.atomic.AtomicReference;
 
@@ -62,7 +61,6 @@ public final class CleanerDrop<T> implements Drop<T> {
     }
 
     private static final class GatedRunner<T> extends AtomicReference<T> implements Runnable {
-        @Serial
         private static final long serialVersionUID = 2685535951915798850L;
         final Drop<T> drop;
 

buffer-api/src/main/java/io/netty/buffer/api/internal/Statics.java

@@ -0,0 +1,170 @@
+/*
+ * Copyright 2020 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:
+ *
+ *   https://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.api.internal;
+
+import io.netty.buffer.api.Buffer;
+import io.netty.buffer.api.Drop;
+
+import java.lang.invoke.MethodHandle;
+import java.lang.invoke.MethodHandles;
+import java.lang.invoke.MethodHandles.Lookup;
+import java.lang.invoke.MethodType;
+import java.lang.invoke.VarHandle;
+import java.lang.ref.Cleaner;
+import java.nio.ByteBuffer;
+import java.nio.ByteOrder;
+import java.util.concurrent.atomic.LongAdder;
+
+public interface Statics {
+    LongAdder MEM_USAGE_NATIVE = new LongAdder();
+    Cleaner CLEANER = Cleaner.create();
+    Drop<Buffer> NO_OP_DROP = new Drop<Buffer>() {
+        @Override
+        public void drop(Buffer obj) {
+        }
+
+        @Override
+        public String toString() {
+            return "NO_OP_DROP";
+        }
+    };
+    MethodHandle BB_SLICE_OFFSETS = getByteBufferSliceOffsetsMethodHandle();
+    MethodHandle BB_PUT_OFFSETS = getByteBufferPutOffsetsMethodHandle();
+
+    static MethodHandle getByteBufferSliceOffsetsMethodHandle() {
+        try {
+            Lookup lookup = MethodHandles.lookup();
+            MethodType type = MethodType.methodType(ByteBuffer.class, int.class, int.class);
+            return lookup.findVirtual(ByteBuffer.class, "slice", type);
+        } catch (Exception ignore) {
+            return null;
+        }
+    }
+
+    static MethodHandle getByteBufferPutOffsetsMethodHandle() {
+        try {
+            Lookup lookup = MethodHandles.lookup();
+            MethodType type = MethodType.methodType(ByteBuffer.class, int.class, ByteBuffer.class, int.class, int.class);
+            return lookup.findVirtual(ByteBuffer.class, "put", type);
+        } catch (Exception ignore) {
+            return null;
+        }
+    }
+
+    static VarHandle findVarHandle(Lookup lookup, Class<?> recv, String name, Class<?> type) {
+        try {
+            return lookup.findVarHandle(recv, name, type);
+        } catch (Exception e) {
+            throw new ExceptionInInitializerError(e);
+        }
+    }
+
+    @SuppressWarnings("unchecked")
+    static <T, R> Drop<R> convert(Drop<T> drop) {
+        return (Drop<R>) drop;
+    }
+
+    static void copyToViaReverseCursor(Buffer src, int srcPos, Buffer dest, int destPos, int length) {
+        // Iterate in reverse to account for src and dest buffer overlap.
+        var itr = src.openReverseCursor(srcPos + length - 1, length);
+        ByteOrder prevOrder = dest.order();
+        // We read longs in BE, in reverse, so they need to be flipped for writing.
+        dest.order(ByteOrder.LITTLE_ENDIAN);
+        try {
+            while (itr.readLong()) {
+                long val = itr.getLong();
+                length -= Long.BYTES;
+                dest.setLong(destPos + length, val);
+            }
+            while (itr.readByte()) {
+                dest.setByte(destPos + --length, itr.getByte());
+            }
+        } finally {
+            dest.order(prevOrder);
+        }
+    }
+
+    /**
+     * The ByteBuffer slice-with-offset-and-length method is only available from Java 13 and onwards, but we need to
+     * support Java 11.
+     */
+    static ByteBuffer bbslice(ByteBuffer buffer, int fromOffset, int length) {
+        if (BB_SLICE_OFFSETS != null) {
+            return bbsliceJdk13(buffer, fromOffset, length);
+        }
+        return bbsliceFallback(buffer, fromOffset, length);
+    }
+
+    private static ByteBuffer bbsliceJdk13(ByteBuffer buffer, int fromOffset, int length) {
+        try {
+            return (ByteBuffer) BB_SLICE_OFFSETS.invokeExact(buffer, fromOffset, length);
+        } catch (RuntimeException re) {
+            throw re;
+        } catch (Throwable throwable) {
+            throw new LinkageError("Unexpected exception from ByteBuffer.slice(int,int).", throwable);
+        }
+    }
+
+    private static ByteBuffer bbsliceFallback(ByteBuffer buffer, int fromOffset, int length) {
+        if (fromOffset < 0) {
+            throw new IndexOutOfBoundsException("The fromOffset must be positive: " + fromOffset + '.');
+        }
+        int newLimit = fromOffset + length;
+        if (newLimit > buffer.capacity()) {
+            throw new IndexOutOfBoundsException(
+                    "The limit of " + newLimit + " would be greater than capacity: " + buffer.capacity() + '.');
+        }
+        try {
+            return buffer.position(fromOffset).limit(newLimit).slice();
+        } finally {
+            buffer.clear();
+        }
+    }
+
+    /**
+     * The ByteBuffer put-buffer-with-offset-and-length method is not available in Java 11.
+     */
+    static void bbput(ByteBuffer dest, int destPos, ByteBuffer src, int srcPos, int length) {
+        if (BB_PUT_OFFSETS != null) {
+            bbputJdk16(dest, destPos, src, srcPos, length);
+        } else {
+            bbputFallback(dest, destPos, src, srcPos, length);
+        }
+    }
+
+    private static void bbputJdk16(ByteBuffer dest, int destPos, ByteBuffer src, int srcPos, int length) {
+        try {
+            @SuppressWarnings("unused") // We need to cast the return type in order to invokeExact.
+            ByteBuffer ignore = (ByteBuffer) BB_PUT_OFFSETS.invokeExact(dest, destPos, src, srcPos, length);
+        } catch (RuntimeException re) {
+            throw re;
+        } catch (Throwable throwable) {
+            throw new LinkageError("Unexpected exception from ByteBuffer.put(int,ByteBuffer,int,int).", throwable);
+        }
+    }
+
+    private static void bbputFallback(ByteBuffer dest, int destPos, ByteBuffer src, int srcPos, int length) {
+        dest.position(destPos).put(bbslice(src, srcPos, length));
+    }
+
+    static IllegalStateException bufferIsClosed() {
+        return new IllegalStateException("This buffer is closed.");
+    }
+
+    static IllegalStateException bufferIsReadOnly() {
+        return new IllegalStateException("This buffer is read-only.");
+    }
+}

buffer-api/src/main/java/io/netty/buffer/api/pool/PoolArena.java

@@ -20,6 +20,8 @@ import io.netty.buffer.api.Buffer;
 import io.netty.buffer.api.MemoryManager;
 import io.netty.util.internal.StringUtil;
 
+import java.lang.invoke.MethodHandles;
+import java.lang.invoke.VarHandle;
 import java.util.ArrayList;
 import java.util.List;
 import java.util.concurrent.atomic.AtomicInteger;
@@ -29,6 +31,7 @@ import static io.netty.buffer.api.pool.PoolChunk.isSubpage;
 import static java.lang.Math.max;
 
 class PoolArena extends SizeClasses implements PoolArenaMetric, AllocatorControl {
+    private static final VarHandle SUBPAGE_ARRAY = MethodHandles.arrayElementVarHandle(PoolSubpage[].class);
     enum SizeClass {
         Small,
         Normal
@@ -76,9 +79,6 @@ class PoolArena extends SizeClasses implements PoolArenaMetric, AllocatorControl
 
         numSmallSubpagePools = nSubpages;
         smallSubpagePools = newSubpagePoolArray(numSmallSubpagePools);
-        for (int i = 0; i < smallSubpagePools.length; i ++) {
-            smallSubpagePools[i] = newSubpagePoolHead();
-        }
 
         q100 = new PoolChunkList(this, null, 100, Integer.MAX_VALUE, chunkSize);
         q075 = new PoolChunkList(this, q100, 75, 100, chunkSize);
@@ -135,7 +135,7 @@ class PoolArena extends SizeClasses implements PoolArenaMetric, AllocatorControl
          * Synchronize on the head. This is needed as {@link PoolChunk#allocateSubpage(int)} and
          * {@link PoolChunk#free(long)} may modify the doubly linked list as well.
          */
-        final PoolSubpage head = smallSubpagePools[sizeIdx];
+        PoolSubpage head = findSubpagePoolHead(sizeIdx);
         final boolean needsNormalAllocation;
         synchronized (head) {
             final PoolSubpage s = head.next;
@@ -246,7 +246,15 @@ class PoolArena extends SizeClasses implements PoolArenaMetric, AllocatorControl
     }
 
     PoolSubpage findSubpagePoolHead(int sizeIdx) {
-        return smallSubpagePools[sizeIdx];
+        PoolSubpage head = (PoolSubpage) SUBPAGE_ARRAY.getVolatile(smallSubpagePools, sizeIdx);
+        if (head == null) {
+            head = newSubpagePoolHead();
+            if (!SUBPAGE_ARRAY.compareAndSet(smallSubpagePools, sizeIdx, null, head)) {
+                // We lost the race. Read the winning value.
+                head = (PoolSubpage) SUBPAGE_ARRAY.getVolatile(smallSubpagePools, sizeIdx);
+            }
+        }
+        return head;
     }
 
     @Override
@@ -288,8 +296,9 @@ class PoolArena extends SizeClasses implements PoolArenaMetric, AllocatorControl
 
     private static List<PoolSubpageMetric> subPageMetricList(PoolSubpage[] pages) {
         List<PoolSubpageMetric> metrics = new ArrayList<>();
-        for (PoolSubpage head : pages) {
-            if (head.next == head) {
+        for (int i = 0, len = pages.length; i < len; i++) {
+            PoolSubpage head = (PoolSubpage) SUBPAGE_ARRAY.getVolatile(pages, i);
+            if (head == null || head.next == head) {
                 continue;
             }
             PoolSubpage s = head.next;
@@ -311,11 +320,6 @@ class PoolArena extends SizeClasses implements PoolArenaMetric, AllocatorControl
         return allocationsSmall.longValue() + allocsNormal + allocationsHuge.longValue();
     }
 
-    @Override
-    public long numTinyAllocations() {
-        return 0;
-    }
-
     @Override
     public long numSmallAllocations() {
         return allocationsSmall.longValue();
@@ -335,11 +339,6 @@ class PoolArena extends SizeClasses implements PoolArenaMetric, AllocatorControl
         return deallocs + deallocationsHuge.longValue();
     }
 
-    @Override
-    public long numTinyDeallocations() {
-        return 0;
-    }
-
     @Override
     public synchronized long numSmallDeallocations() {
         return deallocationsSmall;
@@ -442,8 +441,8 @@ class PoolArena extends SizeClasses implements PoolArenaMetric, AllocatorControl
 
     private static void appendPoolSubPages(StringBuilder buf, PoolSubpage[] subpages) {
         for (int i = 0; i < subpages.length; i ++) {
-            PoolSubpage head = subpages[i];
-            if (head.next == head) {
+            PoolSubpage head = (PoolSubpage) SUBPAGE_ARRAY.getVolatile(subpages, i);
+            if (head == null || head.next == head) {
                 continue;
             }
 
@@ -459,9 +458,12 @@ class PoolArena extends SizeClasses implements PoolArenaMetric, AllocatorControl
     }
 
     public void close() {
-        for (PoolSubpage page : smallSubpagePools) {
+        for (int i = 0, len = smallSubpagePools.length; i < len; i++) {
+            PoolSubpage page = (PoolSubpage) SUBPAGE_ARRAY.getVolatile(smallSubpagePools, i);
+            if (page != null) {
                 page.destroy();
             }
+        }
         for (PoolChunkList list : new PoolChunkList[] {qInit, q000, q025, q050, q100}) {
             list.destroy();
         }

buffer-api/src/main/java/io/netty/buffer/api/pool/PoolArenaMetric.java

@@ -52,14 +52,6 @@ public interface PoolArenaMetric extends SizeClassesMetric {
      */
     long numAllocations();
 
-    /**
-     * Return the number of tiny allocations done via the arena.
-     *
-     * @deprecated Tiny allocations have been merged into small allocations.
-     */
-    @Deprecated
-    long numTinyAllocations();
-
     /**
      * Return the number of small allocations done via the arena.
      */
@@ -80,14 +72,6 @@ public interface PoolArenaMetric extends SizeClassesMetric {
      */
     long numDeallocations();
 
-    /**
-     * Return the number of tiny deallocations done via the arena.
-     *
-     * @deprecated Tiny deallocations have been merged into small deallocations.
-     */
-    @Deprecated
-    long numTinyDeallocations();
-
     /**
      * Return the number of small deallocations done via the arena.
      */

buffer-api/src/main/java/io/netty/buffer/api/pool/PoolChunk.java

@@ -15,12 +15,12 @@
  */
 package io.netty.buffer.api.pool;
 
+import io.netty.buffer.api.internal.CleanerDrop;
 import io.netty.buffer.api.AllocatorControl.UntetheredMemory;
 import io.netty.buffer.api.Buffer;
 import io.netty.buffer.api.Drop;
 import io.netty.buffer.api.MemoryManager;
 import io.netty.buffer.api.internal.ArcDrop;
-import io.netty.buffer.api.internal.CleanerDrop;
 import io.netty.buffer.api.internal.Statics;
 
 import java.util.PriorityQueue;

buffer-api/src/main/java/io/netty/buffer/api/pool/PooledBufferAllocator.java

@@ -431,8 +431,9 @@ public class PooledBufferAllocator implements BufferAllocator, BufferAllocatorMe
         protected void onRemoval(PoolThreadCache threadCache) {
             threadCache.free();
         }
+    }
 
-        private static PoolArena leastUsedArena(PoolArena[] arenas) {
+    static PoolArena leastUsedArena(PoolArena[] arenas) {
         if (arenas == null || arenas.length == 0) {
             return null;
         }
@@ -447,7 +448,6 @@ public class PooledBufferAllocator implements BufferAllocator, BufferAllocatorMe
 
         return minArena;
     }
-    }
 
     @Override
     public PooledBufferAllocatorMetric metric() {

buffer-api/src/main/java/io/netty/buffer/api/pool/SizeClasses.java

@@ -15,7 +15,7 @@
  */
 package io.netty.buffer.api.pool;
 
-import static io.netty.buffer.api.pool.PoolThreadCache.*;
+import java.util.concurrent.ConcurrentHashMap;
 
 /**
  * SizeClasses requires {@code pageShifts} to be defined prior to inclusion,
@@ -79,13 +79,14 @@ import static io.netty.buffer.api.pool.PoolThreadCache.*;
  *   ( 76,    24,       22,        1,       yes,            no,        no)
  */
 abstract class SizeClasses implements SizeClassesMetric {
+    private static final ConcurrentHashMap<SizeClassKey, SizeClassValue> CACHE =
+            new ConcurrentHashMap<SizeClassKey, SizeClassValue>();
 
     static final int LOG2_QUANTUM = 4;
 
     private static final int LOG2_SIZE_CLASS_GROUP = 2;
     private static final int LOG2_MAX_LOOKUP_SIZE = 12;
 
-    private static final int INDEX_IDX = 0;
     private static final int LOG2GROUP_IDX = 1;
     private static final int LOG2DELTA_IDX = 2;
     private static final int NDELTA_IDX = 3;
@@ -101,20 +102,17 @@ abstract class SizeClasses implements SizeClassesMetric {
         this.chunkSize = chunkSize;
         this.directMemoryCacheAlignment = directMemoryCacheAlignment;
 
-        int group = log2(chunkSize) + 1 - LOG2_QUANTUM;
-
-        //generate size classes
-        //[index, log2Group, log2Delta, nDelta, isMultiPageSize, isSubPage, log2DeltaLookup]
-        sizeClasses = new short[group << LOG2_SIZE_CLASS_GROUP][7];
-        nSizes = sizeClasses();
-
-        //generate lookup table
-        sizeIdx2sizeTab = new int[nSizes];
-        pageIdx2sizeTab = new int[nPSizes];
-        idx2SizeTab(sizeIdx2sizeTab, pageIdx2sizeTab);
-
-        size2idxTab = new int[lookupMaxSize >> LOG2_QUANTUM];
-        size2idxTab(size2idxTab);
+        SizeClassValue value = CACHE.computeIfAbsent(
+                new SizeClassKey(pageSize, pageShifts, chunkSize, directMemoryCacheAlignment),
+                SizeClassValue::new);
+        nSizes = value.nSizes;
+        nSubpages = value.nSubpages;
+        nPSizes = value.nPSizes;
+        smallMaxSizeIdx = value.smallMaxSizeIdx;
+        lookupMaxSize = value.lookupMaxSize;
+        pageIdx2sizeTab = value.pageIdx2sizeTab;
+        sizeIdx2sizeTab = value.sizeIdx2sizeTab;
+        size2idxTab = value.size2idxTab;
     }
 
     protected final int pageSize;
@@ -123,15 +121,11 @@ abstract class SizeClasses implements SizeClassesMetric {
     protected final int directMemoryCacheAlignment;
 
     final int nSizes;
-    int nSubpages;
-    int nPSizes;
-
-    int smallMaxSizeIdx;
-
-    private int lookupMaxSize;
-
-    private final short[][] sizeClasses;
+    final int nSubpages;
+    final int nPSizes;
+    final int smallMaxSizeIdx;
 
+    private final int lookupMaxSize;
     private final int[] pageIdx2sizeTab;
 
     // lookup table for sizeIdx <= smallMaxSizeIdx
@@ -141,125 +135,6 @@ abstract class SizeClasses implements SizeClassesMetric {
     // spacing is 1 << LOG2_QUANTUM, so the size of array is lookupMaxclass >> LOG2_QUANTUM
     private final int[] size2idxTab;
 
-    private int sizeClasses() {
-        int normalMaxSize = -1;
-
-        int index = 0;
-        int size = 0;
-
-        int log2Group = LOG2_QUANTUM;
-        int log2Delta = LOG2_QUANTUM;
-        int ndeltaLimit = 1 << LOG2_SIZE_CLASS_GROUP;
-
-        //First small group, nDelta start at 0.
-        //first size class is 1 << LOG2_QUANTUM
-        int nDelta = 0;
-        while (nDelta < ndeltaLimit) {
-            size = sizeClass(index++, log2Group, log2Delta, nDelta++);
-        }
-        log2Group += LOG2_SIZE_CLASS_GROUP;
-
-        //All remaining groups, nDelta start at 1.
-        while (size < chunkSize) {
-            nDelta = 1;
-
-            while (nDelta <= ndeltaLimit && size < chunkSize) {
-                size = sizeClass(index++, log2Group, log2Delta, nDelta++);
-                normalMaxSize = size;
-            }
-
-            log2Group++;
-            log2Delta++;
-        }
-
-        //chunkSize must be normalMaxSize
-        assert chunkSize == normalMaxSize;
-
-        //return number of size index
-        return index;
-    }
-
-    //calculate size class
-    private int sizeClass(int index, int log2Group, int log2Delta, int nDelta) {
-        short isMultiPageSize;
-        if (log2Delta >= pageShifts) {
-            isMultiPageSize = yes;
-        } else {
-            int pageSize = 1 << pageShifts;
-            int size = (1 << log2Group) + (1 << log2Delta) * nDelta;
-
-            isMultiPageSize = size == size / pageSize * pageSize? yes : no;
-        }
-
-        int log2Ndelta = nDelta == 0? 0 : log2(nDelta);
-
-        byte remove = 1 << log2Ndelta < nDelta? yes : no;
-
-        int log2Size = log2Delta + log2Ndelta == log2Group? log2Group + 1 : log2Group;
-        if (log2Size == log2Group) {
-            remove = yes;
-        }
-
-        short isSubpage = log2Size < pageShifts + LOG2_SIZE_CLASS_GROUP? yes : no;
-
-        int log2DeltaLookup = log2Size < LOG2_MAX_LOOKUP_SIZE ||
-                              log2Size == LOG2_MAX_LOOKUP_SIZE && remove == no
-                ? log2Delta : no;
-
-        short[] sz = {
-                (short) index, (short) log2Group, (short) log2Delta,
-                (short) nDelta, isMultiPageSize, isSubpage, (short) log2DeltaLookup
-        };
-
-        sizeClasses[index] = sz;
-        int size = (1 << log2Group) + (nDelta << log2Delta);
-
-        if (sz[PAGESIZE_IDX] == yes) {
-            nPSizes++;
-        }
-        if (sz[SUBPAGE_IDX] == yes) {
-            nSubpages++;
-            smallMaxSizeIdx = index;
-        }
-        if (sz[LOG2_DELTA_LOOKUP_IDX] != no) {
-            lookupMaxSize = size;
-        }
-        return size;
-    }
-
-    private void idx2SizeTab(int[] sizeIdx2sizeTab, int[] pageIdx2sizeTab) {
-        int pageIdx = 0;
-
-        for (int i = 0; i < nSizes; i++) {
-            short[] sizeClass = sizeClasses[i];
-            int log2Group = sizeClass[LOG2GROUP_IDX];
-            int log2Delta = sizeClass[LOG2DELTA_IDX];
-            int nDelta = sizeClass[NDELTA_IDX];
-
-            int size = (1 << log2Group) + (nDelta << log2Delta);
-            sizeIdx2sizeTab[i] = size;
-
-            if (sizeClass[PAGESIZE_IDX] == yes) {
-                pageIdx2sizeTab[pageIdx++] = size;
-            }
-        }
-    }
-
-    private void size2idxTab(int[] size2idxTab) {
-        int idx = 0;
-        int size = 0;
-
-        for (int i = 0; size <= lookupMaxSize; i++) {
-            int log2Delta = sizeClasses[i][LOG2DELTA_IDX];
-            int times = 1 << log2Delta - LOG2_QUANTUM;
-
-            while (size <= lookupMaxSize && times-- > 0) {
-                size2idxTab[idx++] = i;
-                size = idx + 1 << LOG2_QUANTUM;
-            }
-        }
-    }
-
     @Override
     public int sizeIdx2size(int sizeIdx) {
         return sizeIdx2sizeTab[sizeIdx];
@@ -318,7 +193,7 @@ abstract class SizeClasses implements SizeClassesMetric {
             return size2idxTab[size - 1 >> LOG2_QUANTUM];
         }
 
-        int x = log2((size << 1) - 1);
+        int x = PoolThreadCache.log2((size << 1) - 1);
         int shift = x < LOG2_SIZE_CLASS_GROUP + LOG2_QUANTUM + 1
                 ? 0 : x - (LOG2_SIZE_CLASS_GROUP + LOG2_QUANTUM);
 
@@ -350,7 +225,7 @@ abstract class SizeClasses implements SizeClassesMetric {
             return nPSizes;
         }
 
-        int x = log2((pageSize << 1) - 1);
+        int x = PoolThreadCache.log2((pageSize << 1) - 1);
 
         int shift = x < LOG2_SIZE_CLASS_GROUP + pageShifts
                 ? 0 : x - (LOG2_SIZE_CLASS_GROUP + pageShifts);
@@ -397,11 +272,207 @@ abstract class SizeClasses implements SizeClassesMetric {
     }
 
     private static int normalizeSizeCompute(int size) {
-        int x = log2((size << 1) - 1);
+        int x = PoolThreadCache.log2((size << 1) - 1);
         int log2Delta = x < LOG2_SIZE_CLASS_GROUP + LOG2_QUANTUM + 1
                 ? LOG2_QUANTUM : x - LOG2_SIZE_CLASS_GROUP - 1;
         int delta = 1 << log2Delta;
         int delta_mask = delta - 1;
         return size + delta_mask & ~delta_mask;
     }
+
+    private static final class SizeClassKey {
+        final int pageSize;
+        final int pageShifts;
+        final int chunkSize;
+        final int directMemoryCacheAlignment;
+
+        private SizeClassKey(int pageSize, int pageShifts, int chunkSize, int directMemoryCacheAlignment) {
+            this.pageSize = pageSize;
+            this.pageShifts = pageShifts;
+            this.chunkSize = chunkSize;
+            this.directMemoryCacheAlignment = directMemoryCacheAlignment;
+        }
+
+        @Override
+        public boolean equals(Object o) {
+            if (this == o) {
+                return true;
+            }
+            if (o == null || getClass() != o.getClass()) {
+                return false;
+            }
+
+            SizeClassKey that = (SizeClassKey) o;
+
+            if (pageSize != that.pageSize) {
+                return false;
+            }
+            if (pageShifts != that.pageShifts) {
+                return false;
+            }
+            if (chunkSize != that.chunkSize) {
+                return false;
+            }
+            return directMemoryCacheAlignment == that.directMemoryCacheAlignment;
+        }
+
+        @Override
+        public int hashCode() {
+            int result = pageSize;
+            result = 31 * result + pageShifts;
+            result = 31 * result + chunkSize;
+            result = 31 * result + directMemoryCacheAlignment;
+            return result;
+        }
+    }
+
+    private static final class SizeClassValue {
+        final SizeClassKey key;
+        final int nSizes;
+        int nSubpages;
+        int nPSizes;
+        int smallMaxSizeIdx;
+        int lookupMaxSize;
+        final short[][] sizeClasses;
+        final int[] pageIdx2sizeTab;
+        final int[] sizeIdx2sizeTab;
+        final int[] size2idxTab;
+
+        SizeClassValue(SizeClassKey key) {
+            this.key = key;
+            int group = PoolThreadCache.log2(key.chunkSize) + 1 - LOG2_QUANTUM;
+
+            //generate size classes
+            //[index, log2Group, log2Delta, nDelta, isMultiPageSize, isSubPage, log2DeltaLookup]
+            sizeClasses = new short[group << LOG2_SIZE_CLASS_GROUP][7];
+            nSizes = sizeClasses();
+
+            //generate lookup table
+            sizeIdx2sizeTab = new int[nSizes];
+            pageIdx2sizeTab = new int[nPSizes];
+            idx2SizeTab(sizeIdx2sizeTab, pageIdx2sizeTab);
+
+            size2idxTab = new int[lookupMaxSize >> LOG2_QUANTUM];
+            size2idxTab(size2idxTab);
+        }
+
+        private int sizeClasses() {
+            int normalMaxSize = -1;
+
+            int index = 0;
+            int size = 0;
+
+            int log2Group = LOG2_QUANTUM;
+            int log2Delta = LOG2_QUANTUM;
+            int ndeltaLimit = 1 << LOG2_SIZE_CLASS_GROUP;
+
+            //First small group, nDelta start at 0.
+            //first size class is 1 << LOG2_QUANTUM
+            int nDelta = 0;
+            while (nDelta < ndeltaLimit) {
+                size = sizeClass(index++, log2Group, log2Delta, nDelta++);
+            }
+            log2Group += LOG2_SIZE_CLASS_GROUP;
+
+            //All remaining groups, nDelta start at 1.
+            while (size < key.chunkSize) {
+                nDelta = 1;
+
+                while (nDelta <= ndeltaLimit && size < key.chunkSize) {
+                    size = sizeClass(index++, log2Group, log2Delta, nDelta++);
+                    normalMaxSize = size;
+                }
+
+                log2Group++;
+                log2Delta++;
+            }
+
+            //chunkSize must be normalMaxSize
+            assert key.chunkSize == normalMaxSize;
+
+            //return number of size index
+            return index;
+        }
+
+        //calculate size class
+        private int sizeClass(int index, int log2Group, int log2Delta, int nDelta) {
+            short isMultiPageSize;
+            if (log2Delta >= key.pageShifts) {
+                isMultiPageSize = yes;
+            } else {
+                int pageSize = 1 << key.pageShifts;
+                int size = (1 << log2Group) + (1 << log2Delta) * nDelta;
+
+                isMultiPageSize = size == size / pageSize * pageSize? yes : no;
+            }
+
+            int log2Ndelta = nDelta == 0? 0 : PoolThreadCache.log2(nDelta);
+
+            byte remove = 1 << log2Ndelta < nDelta? yes : no;
+
+            int log2Size = log2Delta + log2Ndelta == log2Group? log2Group + 1 : log2Group;
+            if (log2Size == log2Group) {
+                remove = yes;
+            }
+
+            short isSubpage = log2Size < key.pageShifts + LOG2_SIZE_CLASS_GROUP? yes : no;
+
+            int log2DeltaLookup = log2Size < LOG2_MAX_LOOKUP_SIZE ||
+                    log2Size == LOG2_MAX_LOOKUP_SIZE && remove == no
+                    ? log2Delta : no;
+
+            short[] sz = {
+                    (short) index, (short) log2Group, (short) log2Delta,
+                    (short) nDelta, isMultiPageSize, isSubpage, (short) log2DeltaLookup
+            };
+
+            sizeClasses[index] = sz;
+            int size = (1 << log2Group) + (nDelta << log2Delta);
+
+            if (sz[PAGESIZE_IDX] == yes) {
+                nPSizes++;
+            }
+            if (sz[SUBPAGE_IDX] == yes) {
+                nSubpages++;
+                smallMaxSizeIdx = index;
+            }
+            if (sz[LOG2_DELTA_LOOKUP_IDX] != no) {
+                lookupMaxSize = size;
+            }
+            return size;
+        }
+
+        private void idx2SizeTab(int[] sizeIdx2sizeTab, int[] pageIdx2sizeTab) {
+            int pageIdx = 0;
+
+            for (int i = 0; i < nSizes; i++) {
+                short[] sizeClass = sizeClasses[i];
+                int log2Group = sizeClass[LOG2GROUP_IDX];
+                int log2Delta = sizeClass[LOG2DELTA_IDX];
+                int nDelta = sizeClass[NDELTA_IDX];
+
+                int size = (1 << log2Group) + (nDelta << log2Delta);
+                sizeIdx2sizeTab[i] = size;
+
+                if (sizeClass[PAGESIZE_IDX] == yes) {
+                    pageIdx2sizeTab[pageIdx++] = size;
+                }
+            }
+        }
+
+        private void size2idxTab(int[] size2idxTab) {
+            int idx = 0;
+            int size = 0;
+
+            for (int i = 0; size <= lookupMaxSize; i++) {
+                int log2Delta = sizeClasses[i][LOG2DELTA_IDX];
+                int times = 1 << log2Delta - LOG2_QUANTUM;
+
+                while (size <= lookupMaxSize && times-- > 0) {
+                    size2idxTab[idx++] = i;
+                    size = idx + 1 << LOG2_QUANTUM;
+                }
+            }
+        }
+    }
 }

buffer-api/src/main/java/io/netty/buffer/api/unsafe/UnsafeBuffer.java

@@ -15,9 +15,9 @@
  */
 package io.netty.buffer.api.unsafe;
 
+import io.netty.buffer.api.BufferAllocator;
 import io.netty.buffer.api.AllocatorControl;
 import io.netty.buffer.api.Buffer;
-import io.netty.buffer.api.BufferAllocator;
 import io.netty.buffer.api.ByteCursor;
 import io.netty.buffer.api.Drop;
 import io.netty.buffer.api.Owned;
@@ -34,6 +34,7 @@ import java.lang.ref.Reference;
 import java.nio.ByteBuffer;
 import java.nio.ByteOrder;
 
+import static io.netty.buffer.api.internal.Statics.bbslice;
 import static io.netty.buffer.api.internal.Statics.bufferIsClosed;
 import static io.netty.buffer.api.internal.Statics.bufferIsReadOnly;
 import static io.netty.util.internal.PlatformDependent.BIG_ENDIAN_NATIVE_ORDER;
@@ -596,7 +597,7 @@ class UnsafeBuffer extends RcSupport<Buffer, UnsafeBuffer> implements Buffer, Re
     public ByteBuffer readableBuffer() {
         final ByteBuffer buf;
         if (hasReadableArray()) {
-            buf = ByteBuffer.wrap(readableArray()).slice(readableArrayOffset(), readableArrayLength());
+            buf = bbslice(ByteBuffer.wrap(readableArray()), readableArrayOffset(), readableArrayLength());
         } else {
             buf = PlatformDependent.directBuffer(address + roff, readableBytes());
         }
@@ -640,7 +641,7 @@ class UnsafeBuffer extends RcSupport<Buffer, UnsafeBuffer> implements Buffer, Re
     public ByteBuffer writableBuffer() {
         final ByteBuffer buf;
         if (hasWritableArray()) {
-            buf = ByteBuffer.wrap(writableArray()).slice(writableArrayOffset(), writableArrayLength());
+            buf = bbslice(ByteBuffer.wrap(writableArray()), writableArrayOffset(), writableArrayLength());
         } else {
             buf = PlatformDependent.directBuffer(address + woff, writableBytes());
         }

buffer-api/src/main/java/module-info.java

@@ -0,0 +1,43 @@
+/*
+ * Copyright 2021 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:
+ *
+ *   https://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.
+ */
+import io.netty.buffer.api.MemoryManagers;
+import io.netty.buffer.api.bytebuffer.ByteBufferMemoryManagers;
+import io.netty.buffer.api.unsafe.UnsafeMemoryManagers;
+
+module netty.incubator.buffer {
+    requires io.netty.common;
+    requires io.netty.buffer;
+
+    // Optional dependencies, needed for some examples.
+    requires static java.logging;//todo remove
+
+    exports io.netty.buffer.api;
+    exports io.netty.buffer.api.adaptor;
+
+    exports io.netty.buffer.api.internal to
+            netty.incubator.buffer.memseg,
+            netty.incubator.buffer.tests;
+
+    uses MemoryManagers;
+
+    // Permit reflective access to non-public members.
+    // Also means we don't have to make all test methods etc. public for JUnit to access them.
+    opens io.netty.buffer.api;//todo remove
+
+    provides MemoryManagers with
+            ByteBufferMemoryManagers,
+            UnsafeMemoryManagers;
+}

buffer-memseg-dummy/pom.xml

@@ -0,0 +1,30 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+  ~ Copyright 2021 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:
+  ~
+  ~   https://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.
+  -->
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+
+    <parent>
+        <groupId>io.netty.incubator</groupId>
+        <artifactId>netty-incubator-buffer-parent</artifactId>
+        <version>0.0.1.Final-SNAPSHOT</version>
+    </parent>
+
+    <artifactId>netty-incubator-buffer-memseg-dummy</artifactId>
+    <version>0.0.1.Final-SNAPSHOT</version>
+</project>

buffer-memseg-dummy/src/main/java/module-info.java

@@ -0,0 +1,19 @@
+/*
+ * Copyright 2021 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:
+ *
+ *   https://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.
+ */
+module netty.incubator.buffer.memseg {
+    // Java 11 compatible stand-in module for the memory segment implementation.
+    // We need this module in order for the tests module to pull in the memseg module.
+}

buffer-memseg/pom.xml

@@ -0,0 +1,72 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+
+    <parent>
+        <groupId>io.netty.incubator</groupId>
+        <artifactId>netty-incubator-buffer-parent</artifactId>
+        <version>0.0.1.Final-SNAPSHOT</version>
+    </parent>
+
+    <artifactId>netty-incubator-buffer-memseg</artifactId>
+    <version>0.0.1.Final-SNAPSHOT</version>
+    <name>Netty/Incubator/Buffer MemorySegment</name>
+    <packaging>jar</packaging>
+
+    <dependencies>
+        <dependency>
+            <groupId>io.netty.incubator</groupId>
+            <artifactId>netty-incubator-buffer-api</artifactId>
+        </dependency>
+        <dependency>
+            <groupId>io.netty</groupId>
+            <artifactId>netty-common</artifactId>
+        </dependency>
+        <dependency>
+            <groupId>io.netty</groupId>
+            <artifactId>netty-buffer</artifactId>
+        </dependency>
+        <dependency>
+            <groupId>org.openjdk.jmh</groupId>
+            <artifactId>jmh-core</artifactId>
+        </dependency>
+        <dependency>
+            <groupId>org.openjdk.jmh</groupId>
+            <artifactId>jmh-generator-annprocess</artifactId>
+        </dependency>
+        <dependency>
+            <groupId>org.junit.jupiter</groupId>
+            <artifactId>junit-jupiter-engine</artifactId>
+            <scope>test</scope>
+        </dependency>
+    </dependencies>
+
+    <build>
+        <plugins>
+            <plugin>
+                <artifactId>maven-compiler-plugin</artifactId>
+                <version>3.8.1</version>
+                <configuration>
+                    <compilerVersion>${java.version}</compilerVersion>
+                    <fork>true</fork>
+                    <source>${java.compatibility}</source>
+                    <target>${java.compatibility}</target>
+                    <release>${java.version}</release>
+                    <debug>true</debug>
+                    <optimize>true</optimize>
+                    <showDeprecation>true</showDeprecation>
+                    <showWarnings>true</showWarnings>
+                    <compilerArgument>-Xlint:-options</compilerArgument>
+                    <meminitial>256m</meminitial>
+                    <maxmem>1024m</maxmem>
+                    <compilerArgs>
+                        <arg>--add-modules</arg>
+                        <arg>jdk.incubator.foreign</arg>
+                    </compilerArgs>
+                </configuration>
+            </plugin>
+        </plugins>
+    </build>
+</project>

buffer-memseg/src/main/java/io/netty/buffer/api/memseg/AbstractMemorySegmentManager.java

@@ -15,23 +15,22 @@
  */
 package io.netty.buffer.api.memseg;
 
+import io.netty.buffer.api.internal.ArcDrop;
+import io.netty.buffer.api.internal.Statics;
 import io.netty.buffer.api.AllocatorControl;
 import io.netty.buffer.api.Buffer;
 import io.netty.buffer.api.Drop;
 import io.netty.buffer.api.MemoryManager;
-import io.netty.buffer.api.internal.ArcDrop;
 import jdk.incubator.foreign.MemorySegment;
 import jdk.incubator.foreign.ResourceScope;
 
 import java.lang.ref.Cleaner;
 
-import static io.netty.buffer.api.internal.Statics.convert;
-
 public abstract class AbstractMemorySegmentManager implements MemoryManager {
     @Override
     public Buffer allocateShared(AllocatorControl allocatorControl, long size, Drop<Buffer> drop, Cleaner cleaner) {
         var segment = createSegment(size, cleaner);
-        return new MemSegBuffer(segment, segment, convert(drop), allocatorControl);
+        return new MemSegBuffer(segment, segment, Statics.convert(drop), allocatorControl);
     }
 
     @Override
@@ -45,7 +44,7 @@ public abstract class AbstractMemorySegmentManager implements MemoryManager {
 
     @Override
     public Drop<Buffer> drop() {
-        return convert(MemSegBuffer.SEGMENT_CLOSE);
+        return Statics.convert(MemSegBuffer.SEGMENT_CLOSE);
     }
 
     @Override
@@ -71,7 +70,7 @@ public abstract class AbstractMemorySegmentManager implements MemoryManager {
     @Override
     public Buffer recoverMemory(AllocatorControl allocatorControl, Object recoverableMemory, Drop<Buffer> drop) {
         var segment = (MemorySegment) recoverableMemory;
-        return new MemSegBuffer(segment, segment, convert(ArcDrop.acquire(drop)), allocatorControl);
+        return new MemSegBuffer(segment, segment, Statics.convert(ArcDrop.acquire(drop)), allocatorControl);
     }
 
     @Override

buffer-memseg/src/main/java/io/netty/buffer/api/memseg/MemSegBuffer.java

@@ -17,6 +17,11 @@ package io.netty.buffer.api.memseg;
 
 import io.netty.buffer.ByteBuf;
 import io.netty.buffer.api.BufferAllocator;
+import io.netty.buffer.api.adaptor.BufferIntegratable;
+import io.netty.buffer.api.adaptor.ByteBufAdaptor;
+import io.netty.buffer.api.adaptor.ByteBufAllocatorAdaptor;
+import io.netty.buffer.api.internal.ArcDrop;
+import io.netty.buffer.api.internal.Statics;
 import io.netty.buffer.api.AllocatorControl;
 import io.netty.buffer.api.Buffer;
 import io.netty.buffer.api.ByteCursor;
@@ -27,19 +32,12 @@ import io.netty.buffer.api.WritableComponentProcessor;
 import io.netty.buffer.api.Drop;
 import io.netty.buffer.api.Owned;
 import io.netty.buffer.api.RcSupport;
-import io.netty.buffer.api.adaptor.BufferIntegratable;
-import io.netty.buffer.api.adaptor.ByteBufAdaptor;
-import io.netty.buffer.api.adaptor.ByteBufAllocatorAdaptor;
-import io.netty.buffer.api.internal.ArcDrop;
-import io.netty.buffer.api.internal.Statics;
 import jdk.incubator.foreign.MemorySegment;
 import jdk.incubator.foreign.ResourceScope;
 
 import java.nio.ByteBuffer;
 import java.nio.ByteOrder;
 
-import static io.netty.buffer.api.internal.Statics.bufferIsClosed;
-import static io.netty.buffer.api.internal.Statics.bufferIsReadOnly;
 import static jdk.incubator.foreign.MemoryAccess.getByteAtOffset;
 import static jdk.incubator.foreign.MemoryAccess.getCharAtOffset;
 import static jdk.incubator.foreign.MemoryAccess.getDoubleAtOffset;
@@ -325,7 +323,7 @@ class MemSegBuffer extends RcSupport<Buffer, MemSegBuffer> implements Buffer, Re
 
     private void copyInto(int srcPos, MemorySegment dest, int destPos, int length) {
         if (seg == CLOSED_SEGMENT) {
-            throw bufferIsClosed();
+            throw Statics.bufferIsClosed();
         }
         if (srcPos < 0) {
             throw new IllegalArgumentException("The srcPos cannot be negative: " + srcPos + '.');
@@ -360,7 +358,7 @@ class MemSegBuffer extends RcSupport<Buffer, MemSegBuffer> implements Buffer, Re
     @Override
     public ByteCursor openCursor(int fromOffset, int length) {
         if (seg == CLOSED_SEGMENT) {
-            throw bufferIsClosed();
+            throw Statics.bufferIsClosed();
         }
         if (fromOffset < 0) {
             throw new IllegalArgumentException("The fromOffset cannot be negative: " + fromOffset + '.');
@@ -430,7 +428,7 @@ class MemSegBuffer extends RcSupport<Buffer, MemSegBuffer> implements Buffer, Re
     @Override
     public ByteCursor openReverseCursor(int fromOffset, int length) {
         if (seg == CLOSED_SEGMENT) {
-            throw bufferIsClosed();
+            throw Statics.bufferIsClosed();
         }
         if (fromOffset < 0) {
             throw new IllegalArgumentException("The fromOffset cannot be negative: " + fromOffset + '.');
@@ -508,7 +506,7 @@ class MemSegBuffer extends RcSupport<Buffer, MemSegBuffer> implements Buffer, Re
             throw new IllegalArgumentException("The minimum growth cannot be negative: " + minimumGrowth + '.');
         }
         if (seg != wseg) {
-            throw bufferIsReadOnly();
+            throw Statics.bufferIsReadOnly();
         }
         if (writableBytes() >= size) {
             // We already have enough space.
@@ -1172,27 +1170,27 @@ class MemSegBuffer extends RcSupport<Buffer, MemSegBuffer> implements Buffer, Re
 
     private RuntimeException checkWriteState(IndexOutOfBoundsException ioobe) {
         if (seg == CLOSED_SEGMENT) {
-            return bufferIsClosed();
+            return Statics.bufferIsClosed();
         }
         if (wseg != seg) {
-            return bufferIsReadOnly();
+            return Statics.bufferIsReadOnly();
         }
         return ioobe;
     }
 
     private RuntimeException readAccessCheckException(int index) {
         if (seg == CLOSED_SEGMENT) {
-            throw bufferIsClosed();
+            throw Statics.bufferIsClosed();
         }
         return outOfBounds(index);
     }
 
     private RuntimeException writeAccessCheckException(int index) {
         if (seg == CLOSED_SEGMENT) {
-            throw bufferIsClosed();
+            throw Statics.bufferIsClosed();
         }
         if (wseg != seg) {
-            return bufferIsReadOnly();
+            return Statics.bufferIsReadOnly();
         }
         return outOfBounds(index);
     }

buffer-memseg/src/main/java/io/netty/buffer/api/memseg/NativeMemorySegmentManager.java

@@ -15,18 +15,17 @@
  */
 package io.netty.buffer.api.memseg;
 
+import io.netty.buffer.api.internal.Statics;
 import jdk.incubator.foreign.MemorySegment;
 import jdk.incubator.foreign.ResourceScope;
 
 import java.lang.ref.Cleaner;
 import java.util.concurrent.ConcurrentHashMap;
-import java.util.concurrent.atomic.LongAdder;
 import java.util.function.Function;
 
 import static jdk.incubator.foreign.ResourceScope.newSharedScope;
 
 public class NativeMemorySegmentManager extends AbstractMemorySegmentManager {
-    public static final LongAdder MEM_USAGE_NATIVE = new LongAdder();
     private static final ConcurrentHashMap<Long, Runnable> CLEANUP_ACTIONS = new ConcurrentHashMap<>();
     private static final Function<Long, Runnable> CLEANUP_ACTION_MAKER = s -> new ReduceNativeMemoryUsage(s);
 
@@ -43,7 +42,7 @@ public class NativeMemorySegmentManager extends AbstractMemorySegmentManager {
 
         @Override
         public void run() {
-            MEM_USAGE_NATIVE.add(-size);
+            Statics.MEM_USAGE_NATIVE.add(-size);
         }
 
         @Override
@@ -62,7 +61,7 @@ public class NativeMemorySegmentManager extends AbstractMemorySegmentManager {
         final ResourceScope scope = cleaner == null ? newSharedScope() : newSharedScope(cleaner);
         scope.addCloseAction(getCleanupAction(size));
         var segment = MemorySegment.allocateNative(size, scope);
-        MEM_USAGE_NATIVE.add(size);
+        Statics.MEM_USAGE_NATIVE.add(size);
         return segment;
     }
 }

buffer-memseg/src/main/java/module-info.java

@@ -13,25 +13,22 @@
  * License for the specific language governing permissions and limitations
  * under the License.
  */
-module netty.incubator.buffer {
+import io.netty.buffer.api.MemoryManagers;
+import io.netty.buffer.api.memseg.SegmentMemoryManagers;
+
+module netty.incubator.buffer.memseg {
     requires jdk.incubator.foreign;
     requires io.netty.common;
     requires io.netty.buffer;
+    requires netty.incubator.buffer;
 
     // Optional dependencies, needed for some examples.
     requires static java.logging;
 
-    exports io.netty.buffer.api;
-    exports io.netty.buffer.api.adaptor;
-
-    uses io.netty.buffer.api.MemoryManagers;
-
     // Permit reflective access to non-public members.
     // Also means we don't have to make all test methods etc. public for JUnit to access them.
-    opens io.netty.buffer.api;
+    opens io.netty.buffer.api.memseg;
 
-    provides io.netty.buffer.api.MemoryManagers with
-            io.netty.buffer.api.memseg.SegmentMemoryManagers,
-            io.netty.buffer.api.bytebuffer.ByteBufferMemoryManagers,
-            io.netty.buffer.api.unsafe.UnsafeMemoryManagers;
+    provides MemoryManagers with
+            SegmentMemoryManagers;
 }

buffer-memseg/src/test/java/io/netty/buffer/api/memseg/benchmarks/MemSegBufAccessBenchmark.java

@@ -13,7 +13,7 @@
 * License for the specific language governing permissions and limitations
 * under the License.
 */
-package io.netty.buffer.api.benchmarks;
+package io.netty.buffer.api.memseg.benchmarks;
 
 import io.netty.buffer.api.BufferAllocator;
 import io.netty.buffer.api.Buffer;

buffer-memseg/src/test/java/io/netty/buffer/api/memseg/benchmarks/MemorySegmentCloseBenchmark.java

@@ -13,7 +13,7 @@
  * License for the specific language governing permissions and limitations
  * under the License.
  */
-package io.netty.buffer.api.benchmarks;
+package io.netty.buffer.api.memseg.benchmarks;
 
 import jdk.incubator.foreign.MemorySegment;
 import jdk.incubator.foreign.ResourceScope;

buffer-memseg/src/test/java/io/netty/buffer/api/memseg/benchmarks/MemorySegmentClosedByCleanerBenchmark.java

@@ -13,10 +13,12 @@
  * License for the specific language governing permissions and limitations
  * under the License.
  */
-package io.netty.buffer.api.benchmarks;
+package io.netty.buffer.api.memseg.benchmarks;
 
 import io.netty.buffer.api.BufferAllocator;
+import io.netty.buffer.api.memseg.SegmentMemoryManagers;
 import io.netty.buffer.api.Buffer;
+import io.netty.buffer.api.MemoryManagers;
 import org.openjdk.jmh.annotations.Benchmark;
 import org.openjdk.jmh.annotations.BenchmarkMode;
 import org.openjdk.jmh.annotations.Fork;
@@ -41,10 +43,37 @@ import static java.util.concurrent.CompletableFuture.completedFuture;
 @OutputTimeUnit(TimeUnit.MICROSECONDS)
 @State(Scope.Benchmark)
 public class MemorySegmentClosedByCleanerBenchmark {
-    private static final BufferAllocator heap = BufferAllocator.heap();
-    private static final BufferAllocator heapPooled = BufferAllocator.pooledHeap();
-    private static final BufferAllocator direct = BufferAllocator.direct();
-    private static final BufferAllocator directPooled = BufferAllocator.pooledDirect();
+    private static final BufferAllocator heap;
+    private static final BufferAllocator heapPooled;
+    private static final BufferAllocator direct;
+    private static final BufferAllocator directPooled;
+
+    static {
+        class Allocators {
+            final BufferAllocator heap;
+            final BufferAllocator pooledHeap;
+            final BufferAllocator direct;
+            final BufferAllocator pooledDirect;
+
+            Allocators(BufferAllocator heap, BufferAllocator pooledHeap,
+                       BufferAllocator direct, BufferAllocator pooledDirect) {
+                this.heap = heap;
+                this.pooledHeap = pooledHeap;
+                this.direct = direct;
+                this.pooledDirect = pooledDirect;
+            }
+        }
+
+        var allocs = MemoryManagers.using(new SegmentMemoryManagers(), () -> {
+            return new Allocators(BufferAllocator.heap(), BufferAllocator.pooledHeap(),
+                    BufferAllocator.direct(), BufferAllocator.pooledDirect());
+        });
+
+        heap = allocs.heap;
+        heapPooled = allocs.pooledHeap;
+        direct = allocs.direct;
+        directPooled = allocs.pooledDirect;
+    }
 
     @Param({"heavy", "light"})
     public String workload;

buffer-tests/pom.xml

@@ -0,0 +1,123 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+  ~ Copyright 2021 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:
+  ~
+  ~   https://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.
+  -->
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+
+    <parent>
+        <groupId>io.netty.incubator</groupId>
+        <artifactId>netty-incubator-buffer-parent</artifactId>
+        <version>0.0.1.Final-SNAPSHOT</version>
+    </parent>
+
+    <artifactId>netty-incubator-buffer-tests</artifactId>
+    <version>0.0.1.Final-SNAPSHOT</version>
+    <name>Netty/Incubator/Buffer Tests</name>
+    <packaging>jar</packaging>
+
+    <dependencies>
+        <dependency>
+            <groupId>io.netty.incubator</groupId>
+            <artifactId>netty-incubator-buffer-api</artifactId>
+        </dependency>
+        <dependency>
+            <groupId>org.junit.jupiter</groupId>
+            <artifactId>junit-jupiter-api</artifactId>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.junit.jupiter</groupId>
+            <artifactId>junit-jupiter-engine</artifactId>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.junit.jupiter</groupId>
+            <artifactId>junit-jupiter-params</artifactId>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.junit.vintage</groupId>
+            <artifactId>junit-vintage-engine</artifactId>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>junit</groupId>
+            <artifactId>junit</artifactId>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.assertj</groupId>
+            <artifactId>assertj-core</artifactId>
+        </dependency>
+        <dependency>
+            <groupId>org.mockito</groupId>
+            <artifactId>mockito-core</artifactId>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>io.netty</groupId>
+            <artifactId>netty-build-common</artifactId>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>io.netty</groupId>
+            <artifactId>netty-handler</artifactId>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>io.netty</groupId>
+            <artifactId>netty-codec-http</artifactId>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.openjdk.jmh</groupId>
+            <artifactId>jmh-core</artifactId>
+        </dependency>
+        <dependency>
+            <groupId>org.openjdk.jmh</groupId>
+            <artifactId>jmh-generator-annprocess</artifactId>
+        </dependency>
+    </dependencies>
+
+    <profiles>
+        <profile>
+            <id>Java 17 support</id>
+            <activation>
+                <jdk>17</jdk>
+            </activation>
+            <dependencies>
+                <dependency>
+                    <groupId>io.netty.incubator</groupId>
+                    <artifactId>netty-incubator-buffer-memseg</artifactId>
+                </dependency>
+            </dependencies>
+        </profile>
+        <profile>
+            <id>Java 11 support for tests</id>
+            <activation>
+                <jdk>!17</jdk>
+            </activation>
+            <dependencies>
+                <dependency>
+                    <groupId>io.netty.incubator</groupId>
+                    <artifactId>netty-incubator-buffer-memseg-dummy</artifactId>
+                </dependency>
+            </dependencies>
+        </profile>
+    </profiles>
+</project>

buffer-tests/src/main/java/module-info.java

@@ -0,0 +1,27 @@
+/*
+ * Copyright 2021 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:
+ *
+ *   https://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.
+ */
+open module netty.incubator.buffer.tests {
+    requires io.netty.common;
+    requires io.netty.buffer;
+
+    // Optional dependencies, needed for some examples.
+    requires static java.logging;
+
+    requires netty.incubator.buffer;
+    // We need to require memseg in order for its implementation to be service loaded.
+    // Just having it on the module path is not enough.
+    requires netty.incubator.buffer.memseg;
+}

buffer-tests/src/test/java/io/netty/buffer/api/tests/BufferBulkAccessTest.java

@@ -13,8 +13,12 @@
  * License for the specific language governing permissions and limitations
  * under the License.
  */
-package io.netty.buffer.api;
+package io.netty.buffer.api.tests;
 
+import io.netty.buffer.api.Buffer;
+import io.netty.buffer.api.BufferAllocator;
+import io.netty.buffer.api.CompositeBuffer;
+import io.netty.buffer.api.Scope;
 import org.junit.jupiter.params.ParameterizedTest;
 import org.junit.jupiter.params.provider.MethodSource;
 

buffer-tests/src/test/java/io/netty/buffer/api/tests/BufferByteOffsettedAccessorsTest.java

@@ -13,8 +13,10 @@
  * License for the specific language governing permissions and limitations
  * under the License.
  */
-package io.netty.buffer.api;
+package io.netty.buffer.api.tests;
 
+import io.netty.buffer.api.Buffer;
+import io.netty.buffer.api.BufferAllocator;
 import org.junit.jupiter.params.ParameterizedTest;
 import org.junit.jupiter.params.provider.MethodSource;
 

buffer-tests/src/test/java/io/netty/buffer/api/tests/BufferCharOffsettedAccessorsTest.java

@@ -13,8 +13,10 @@
  * License for the specific language governing permissions and limitations
  * under the License.
  */
-package io.netty.buffer.api;
+package io.netty.buffer.api.tests;
 
+import io.netty.buffer.api.Buffer;
+import io.netty.buffer.api.BufferAllocator;
 import org.junit.jupiter.params.ParameterizedTest;
 import org.junit.jupiter.params.provider.MethodSource;
 

buffer-tests/src/test/java/io/netty/buffer/api/tests/BufferCleanerTest.java

@@ -13,13 +13,17 @@
  * License for the specific language governing permissions and limitations
  * under the License.
  */
-package io.netty.buffer.api;
+package io.netty.buffer.api.tests;
 
-import io.netty.buffer.api.memseg.NativeMemorySegmentManager;
+import io.netty.buffer.api.MemoryManagers;
+import io.netty.buffer.api.internal.Statics;
+import org.junit.jupiter.api.condition.DisabledForJreRange;
+import org.junit.jupiter.api.condition.JRE;
 import org.junit.jupiter.params.ParameterizedTest;
 import org.junit.jupiter.params.provider.MethodSource;
 
 import java.util.List;
+import java.util.stream.Collectors;
 import java.util.stream.Stream;
 
 import static io.netty.buffer.api.MemoryManagers.using;
@@ -36,21 +40,23 @@ public class BufferCleanerTest extends BufferTestSupport {
             Stream.Builder<Fixture> builder = Stream.builder();
             builder.add(new Fixture(f + "/" + managers, () -> using(managers, f), f.getProperties()));
             return builder.build();
-        }).toList();
+        }).collect(Collectors.toList());
         return fixtureCombinations(initFixtures).filter(f -> f.isDirect()).toArray(Fixture[]::new);
     }
 
+    // Only run this one on JDK 17.
+    @DisabledForJreRange(min = JRE.JAVA_11, max = JRE.JAVA_16)
     @ParameterizedTest
     @MethodSource("memorySegmentAllocators")
     public void bufferMustBeClosedByCleaner(Fixture fixture) throws InterruptedException {
-        var initial = NativeMemorySegmentManager.MEM_USAGE_NATIVE.sum();
+        var initial = Statics.MEM_USAGE_NATIVE.sum();
         int allocationSize = 1024;
         allocateAndForget(fixture, allocationSize);
         long sum = 0;
         for (int i = 0; i < 15; i++) {
             System.gc();
             System.runFinalization();
-            sum = NativeMemorySegmentManager.MEM_USAGE_NATIVE.sum() - initial;
+            sum = Statics.MEM_USAGE_NATIVE.sum() - initial;
             if (sum < allocationSize) {
                 // The memory must have been cleaned.
                 return;

buffer-tests/src/test/java/io/netty/buffer/api/tests/BufferCompactTest.java

@@ -13,8 +13,10 @@
  * License for the specific language governing permissions and limitations
  * under the License.
  */
-package io.netty.buffer.api;
+package io.netty.buffer.api.tests;
 
+import io.netty.buffer.api.Buffer;
+import io.netty.buffer.api.BufferAllocator;
 import org.junit.jupiter.params.ParameterizedTest;
 import org.junit.jupiter.params.provider.MethodSource;
 

buffer-tests/src/test/java/io/netty/buffer/api/tests/BufferComponentIterationTest.java

@@ -13,8 +13,12 @@
  * License for the specific language governing permissions and limitations
  * under the License.
  */
-package io.netty.buffer.api;
+package io.netty.buffer.api.tests;
 
+import io.netty.buffer.api.Buffer;
+import io.netty.buffer.api.BufferAllocator;
+import io.netty.buffer.api.ByteCursor;
+import io.netty.buffer.api.CompositeBuffer;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.params.ParameterizedTest;
 import org.junit.jupiter.params.provider.MethodSource;

buffer-tests/src/test/java/io/netty/buffer/api/tests/BufferCompositionTest.java

@@ -13,8 +13,11 @@
  * License for the specific language governing permissions and limitations
  * under the License.
  */
-package io.netty.buffer.api;
+package io.netty.buffer.api.tests;
 
+import io.netty.buffer.api.Buffer;
+import io.netty.buffer.api.BufferAllocator;
+import io.netty.buffer.api.CompositeBuffer;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.params.ParameterizedTest;
 import org.junit.jupiter.params.provider.MethodSource;

buffer-tests/src/test/java/io/netty/buffer/api/tests/BufferDoubleOffsettedAccessorsTest.java

@@ -13,8 +13,10 @@
  * License for the specific language governing permissions and limitations
  * under the License.
  */
-package io.netty.buffer.api;
+package io.netty.buffer.api.tests;
 
+import io.netty.buffer.api.Buffer;
+import io.netty.buffer.api.BufferAllocator;
 import org.junit.jupiter.params.ParameterizedTest;
 import org.junit.jupiter.params.provider.MethodSource;
 

buffer-tests/src/test/java/io/netty/buffer/api/tests/BufferEnsureWritableTest.java

@@ -13,8 +13,11 @@
  * License for the specific language governing permissions and limitations
  * under the License.
  */
-package io.netty.buffer.api;
+package io.netty.buffer.api.tests;
 
+import io.netty.buffer.api.Buffer;
+import io.netty.buffer.api.BufferAllocator;
+import io.netty.buffer.api.CompositeBuffer;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.params.ParameterizedTest;
 import org.junit.jupiter.params.provider.MethodSource;

buffer-tests/src/test/java/io/netty/buffer/api/tests/BufferFloatOffsettedAccessorsTest.java

@@ -13,8 +13,10 @@
  * License for the specific language governing permissions and limitations
  * under the License.
  */
-package io.netty.buffer.api;
+package io.netty.buffer.api.tests;
 
+import io.netty.buffer.api.Buffer;
+import io.netty.buffer.api.BufferAllocator;
 import org.junit.jupiter.params.ParameterizedTest;
 import org.junit.jupiter.params.provider.MethodSource;
 

buffer-tests/src/test/java/io/netty/buffer/api/tests/BufferIntOffsettedAccessorsTest.java

@@ -13,8 +13,10 @@
  * License for the specific language governing permissions and limitations
  * under the License.
  */
-package io.netty.buffer.api;
+package io.netty.buffer.api.tests;
 
+import io.netty.buffer.api.Buffer;
+import io.netty.buffer.api.BufferAllocator;
 import org.junit.jupiter.params.ParameterizedTest;
 import org.junit.jupiter.params.provider.MethodSource;
 

buffer-tests/src/test/java/io/netty/buffer/api/tests/BufferLongOffsettedAccessorsTest.java

@@ -13,8 +13,10 @@
  * License for the specific language governing permissions and limitations
  * under the License.
  */
-package io.netty.buffer.api;
+package io.netty.buffer.api.tests;
 
+import io.netty.buffer.api.Buffer;
+import io.netty.buffer.api.BufferAllocator;
 import org.junit.jupiter.params.ParameterizedTest;
 import org.junit.jupiter.params.provider.MethodSource;
 

buffer-tests/src/test/java/io/netty/buffer/api/tests/BufferMediumOffsettedAccessorsTest.java

@@ -13,8 +13,10 @@
  * License for the specific language governing permissions and limitations
  * under the License.
  */
-package io.netty.buffer.api;
+package io.netty.buffer.api.tests;
 
+import io.netty.buffer.api.Buffer;
+import io.netty.buffer.api.BufferAllocator;
 import org.junit.jupiter.params.ParameterizedTest;
 import org.junit.jupiter.params.provider.MethodSource;
 

buffer-tests/src/test/java/io/netty/buffer/api/tests/BufferOffsetsTest.java

@@ -13,8 +13,10 @@
  * License for the specific language governing permissions and limitations
  * under the License.
  */
-package io.netty.buffer.api;
+package io.netty.buffer.api.tests;
 
+import io.netty.buffer.api.Buffer;
+import io.netty.buffer.api.BufferAllocator;
 import org.junit.jupiter.params.ParameterizedTest;
 import org.junit.jupiter.params.provider.MethodSource;