Allow efficient writing of CompositeByteBuf when using native epoll transport.

Motivation:

There were no way to efficient write a CompositeByteBuf as we always did a memory copy to a direct buffer in this case. This is not needed as we can just write a CompositeByteBuf as long as all the components are buffers with a memory address.

Modifications:

- Write CompositeByteBuf which contains only direct buffers without memory copy
- Also handle CompositeByteBuf that have more components then 1024.

Result:

More efficient writing of CompositeByteBuf.

transport-native-epoll/src/main/java/io/netty/channel/epoll/EpollSocketChannel.java

@@ -17,6 +17,7 @@ package io.netty.channel.epoll;
 
 import io.netty.buffer.ByteBuf;
 import io.netty.buffer.ByteBufAllocator;
+import io.netty.buffer.CompositeByteBuf;
 import io.netty.channel.Channel;
 import io.netty.channel.ChannelConfig;
 import io.netty.channel.ChannelFuture;
@@ -392,11 +393,22 @@ public final class EpollSocketChannel extends AbstractEpollChannel implements So
         if (msg instanceof ByteBuf) {
             ByteBuf buf = (ByteBuf) msg;
             if (!buf.hasMemoryAddress() && (PlatformDependent.hasUnsafe() || !buf.isDirect())) {
+                if (buf instanceof CompositeByteBuf) {
+                    // Special handling of CompositeByteBuf to reduce memory copies if some of the Components
+                    // in the CompositeByteBuf are backed by a memoryAddress.
+                    CompositeByteBuf comp = (CompositeByteBuf) buf;
+                    if (!comp.isDirect() || comp.nioBufferCount() > Native.IOV_MAX) {
+                        // more then 1024 buffers for gathering writes so just do a memory copy.
+                        buf = newDirectBuffer(buf);
+                        assert buf.hasMemoryAddress();
+                    }
+                } else {
                     // We can only handle buffers with memory address so we need to copy if a non direct is
                     // passed to write.
                     buf = newDirectBuffer(buf);
                     assert buf.hasMemoryAddress();
                 }
+            }
             return buf;
         }
 

transport-native-epoll/src/main/java/io/netty/channel/epoll/IovArray.java

@@ -16,11 +16,14 @@
 package io.netty.channel.epoll;
 
 import io.netty.buffer.ByteBuf;
+import io.netty.buffer.CompositeByteBuf;
 import io.netty.channel.ChannelOutboundBuffer;
 import io.netty.channel.ChannelOutboundBuffer.MessageProcessor;
 import io.netty.util.concurrent.FastThreadLocal;
 import io.netty.util.internal.PlatformDependent;
 
+import java.nio.ByteBuffer;
+
 /**
  * Represent an array of struct array and so can be passed directly over via JNI without the need to do any more
  * array copies.
@@ -95,6 +98,15 @@ final class IovArray implements MessageProcessor {
 
         final long addr = buf.memoryAddress();
         final int offset = buf.readerIndex();
+        add(addr, offset, len);
+        return true;
+    }
+
+    private void add(long addr, int offset, int len) {
+        if (len == 0) {
+            // No need to add an empty buffer.
+            return;
+        }
 
         final long baseOffset = memoryAddress(count++);
         final long lengthOffset = baseOffset + ADDRESS_SIZE;
@@ -110,6 +122,26 @@ final class IovArray implements MessageProcessor {
         }
 
         size += len;
+    }
+
+    private boolean add(CompositeByteBuf buf) {
+        ByteBuffer[] buffers = buf.nioBuffers();
+        if (count + buffers.length >= Native.IOV_MAX) {
+            // No more room!
+            return false;
+        }
+        for (int i = 0; i < buffers.length; i++) {
+            ByteBuffer nioBuffer = buffers[i];
+            int offset = nioBuffer.position();
+            int len = nioBuffer.limit() - nioBuffer.position();
+            if (len == 0) {
+                // No need to add an empty buffer so just continue
+                continue;
+            }
+            long addr = PlatformDependent.directBufferAddress(nioBuffer);
+
+            add(addr, offset, len);
+        }
         return true;
     }
 
@@ -166,7 +198,14 @@ final class IovArray implements MessageProcessor {
 
     @Override
     public boolean processMessage(Object msg) throws Exception {
-        return msg instanceof ByteBuf && add((ByteBuf) msg);
+        if (msg instanceof ByteBuf) {
+            if (msg instanceof CompositeByteBuf) {
+                return add((CompositeByteBuf) msg);
+            } else {
+                return add((ByteBuf) msg);
+            }
+        }
+        return false;
     }
 
     /**