Copies from read-only heap ByteBuffer to direct ByteBuf can avoid stealth ByteBuf allocation and additional copies

Motivation:

Read-only heap ByteBuffer doesn't expose array: the existent method to perform copies to direct ByteBuf involves the creation of a (maybe pooled) additional heap ByteBuf instance and copy

Modifications:

To avoid stressing the allocator with additional (and stealth) heap ByteBuf allocations is provided a method to perform copies using the (pooled) internal NIO buffer

Result:

Copies from read-only heap ByteBuffer to direct ByteBuf won't create any intermediate ByteBuf

buffer/src/main/java/io/netty/buffer/UnsafeByteBufUtil.java

@@ -538,34 +538,48 @@ final class UnsafeByteBufUtil {
     }
 
     static void setBytes(AbstractByteBuf buf, long addr, int index, ByteBuffer src) {
-        buf.checkIndex(index, src.remaining());
-
-        int length = src.remaining();
+        final int length = src.remaining();
         if (length == 0) {
             return;
         }
 
         if (src.isDirect()) {
+            buf.checkIndex(index, length);
             // Copy from direct memory
             long srcAddress = PlatformDependent.directBufferAddress(src);
-            PlatformDependent.copyMemory(srcAddress + src.position(), addr, src.remaining());
+            PlatformDependent.copyMemory(srcAddress + src.position(), addr, length);
             src.position(src.position() + length);
         } else if (src.hasArray()) {
+            buf.checkIndex(index, length);
             // Copy from array
             PlatformDependent.copyMemory(src.array(), src.arrayOffset() + src.position(), addr, length);
             src.position(src.position() + length);
         } else {
-            ByteBuf tmpBuf = buf.alloc().heapBuffer(length);
-            try {
-                byte[] tmp = tmpBuf.array();
-                src.get(tmp, tmpBuf.arrayOffset(), length); // moves the src position too
-                PlatformDependent.copyMemory(tmp, tmpBuf.arrayOffset(), addr, length);
-            } finally {
-                tmpBuf.release();
+            if (length < 8) {
+                setSingleBytes(buf, addr, index, src, length);
+            } else {
+                //no need to checkIndex: internalNioBuffer is already taking care of it
+                assert buf.nioBufferCount() == 1;
+                final ByteBuffer internalBuffer = buf.internalNioBuffer(index, length);
+                internalBuffer.put(src);
             }
         }
     }
 
+    private static void setSingleBytes(final AbstractByteBuf buf, final long addr, final int index,
+                                       final ByteBuffer src, final int length) {
+        buf.checkIndex(index, length);
+        final int srcPosition = src.position();
+        final int srcLimit = src.limit();
+        long dstAddr = addr;
+        for (int srcIndex = srcPosition; srcIndex < srcLimit; srcIndex++) {
+            final byte value = src.get(srcIndex);
+            PlatformDependent.putByte(dstAddr, value);
+            dstAddr++;
+        }
+        src.position(srcLimit);
+    }
+
     static void getBytes(AbstractByteBuf buf, long addr, int index, OutputStream out, int length) throws IOException {
         buf.checkIndex(index, length);
         if (length != 0) {

microbench/src/main/java/io/netty/microbench/buffer/ByteBufCopyBenchmark.java

@@ -0,0 +1,102 @@
+/*
+ * Copyright 2018 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.microbench.buffer;
+
+import io.netty.buffer.ByteBuf;
+import io.netty.buffer.PooledByteBufAllocator;
+import io.netty.buffer.Unpooled;
+import io.netty.microbench.util.AbstractMicrobenchmark;
+import org.openjdk.jmh.annotations.Benchmark;
+import org.openjdk.jmh.annotations.Param;
+import org.openjdk.jmh.annotations.Setup;
+import org.openjdk.jmh.annotations.TearDown;
+
+import java.nio.ByteBuffer;
+import java.nio.ByteOrder;
+
+public class ByteBufCopyBenchmark extends AbstractMicrobenchmark {
+    static {
+        System.setProperty("io.netty.buffer.bytebuf.checkAccessible", "false");
+    }
+
+    @Param({"7", "36", "128", "512" })
+    private int size;
+    @Param({"true", "false" })
+    private boolean directByteBuff;
+    @Param({"true", "false" })
+    private boolean directByteBuffer;
+    @Param({"false", "true" })
+    private boolean readonlyByteBuffer;
+    @Param({"true", "false" })
+    private boolean pooledByteBuf;
+    @Param({"true", "false" })
+    private boolean alignedCopyByteBuffer;
+    @Param({"true", "false" })
+    private boolean alignedCopyByteBuf;
+    @Param({"true", "false" })
+    private boolean nativeOrderByteBuffer;
+
+    private ByteBuffer byteBuffer;
+    private ByteBuf buffer;
+    private int index;
+
+    @Setup
+    public void setup() {
+        final int requiredByteBufSize = alignedCopyByteBuf ? size : size + 1;
+        final int requiredByteBufferSize = alignedCopyByteBuffer ? size : size + 1;
+        byteBuffer = directByteBuffer ?
+                ByteBuffer.allocateDirect(requiredByteBufferSize) :
+                ByteBuffer.allocate(requiredByteBufferSize);
+        if (pooledByteBuf) {
+            buffer = directByteBuff ?
+                    PooledByteBufAllocator.DEFAULT.directBuffer(requiredByteBufSize, requiredByteBufSize) :
+                    PooledByteBufAllocator.DEFAULT.heapBuffer(requiredByteBufSize, requiredByteBufSize);
+        } else {
+            buffer = directByteBuff ?
+                    Unpooled.directBuffer(requiredByteBufSize, requiredByteBufSize) :
+                    Unpooled.buffer(requiredByteBufSize, requiredByteBufSize);
+        }
+        if (!alignedCopyByteBuffer) {
+            byteBuffer.position(1);
+            byteBuffer = byteBuffer.slice();
+        }
+        if (readonlyByteBuffer) {
+            byteBuffer = byteBuffer.asReadOnlyBuffer();
+        }
+        final ByteOrder byteBufferOrder;
+        if (!nativeOrderByteBuffer) {
+            byteBufferOrder = ByteOrder.LITTLE_ENDIAN == ByteOrder.nativeOrder() ?
+                    ByteOrder.BIG_ENDIAN :
+                    ByteOrder.LITTLE_ENDIAN;
+        } else {
+            byteBufferOrder = ByteOrder.nativeOrder();
+        }
+        byteBuffer.order(byteBufferOrder);
+        index = alignedCopyByteBuf ? 0 : 1;
+    }
+
+    @Benchmark
+    public ByteBuf setBytes() {
+        byteBuffer.clear();
+        return buffer.setBytes(index, byteBuffer);
+    }
+
+    @TearDown
+    public void tearDown() {
+        buffer.release();
+    }
+
+}