Overall clean-up in EpollSocketChannel

- Extract writev part from doWrite() for simplicity
- Clearer comments

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

@@ -128,31 +128,8 @@ public final class EpollSocketChannel extends AbstractEpollChannel implements So
         return localFlushedAmount;
     }
 
-    /**
+    private void writeBytesMultiple(
-     * Write a {@link DefaultFileRegion}
+            ChannelOutboundBuffer in, int msgCount, ByteBuffer[] nioBuffers) throws IOException {
-     *
-     * @param region        the {@link DefaultFileRegion} from which the bytes should be written
-     * @return amount       the amount of written bytes
-     */
-    private long doWriteFileRegion(DefaultFileRegion region, long count) throws Exception {
-        return Native.sendfile(fd, region, region.transfered(), count);
-    }
-
-    @Override
-    protected void doWrite(ChannelOutboundBuffer in) throws Exception {
-        for (;;) {
-            final int msgCount = in.size();
-
-            if (msgCount == 0) {
-                // Wrote all messages.
-                clearEpollOut();
-                break;
-            }
-            // Do non-gathering write for a single buffer case.
-            if (msgCount > 1) {
-                // Ensure the pending writes are made of ByteBufs only.
-                ByteBuffer[] nioBuffers = in.nioBuffers();
-                if (nioBuffers != null) {
 
         int nioBufferCnt = in.nioBufferCount();
         long expectedWrittenBytes = in.nioBufferSize();
@@ -188,11 +165,46 @@ public final class EpollSocketChannel extends AbstractEpollChannel implements So
                 in.remove();
             }
         }
-                    // try again as a ChannelFuture may be notified in the meantime and triggered another flush
+    }
+
+    /**
+     * Write a {@link DefaultFileRegion}
+     *
+     * @param region        the {@link DefaultFileRegion} from which the bytes should be written
+     * @return amount       the amount of written bytes
+     */
+    private long doWriteFileRegion(DefaultFileRegion region, long count) throws Exception {
+        return Native.sendfile(fd, region, region.transfered(), count);
+    }
+
+    @Override
+    protected void doWrite(ChannelOutboundBuffer in) throws Exception {
+        for (;;) {
+            final int msgCount = in.size();
+
+            if (msgCount == 0) {
+                // Wrote all messages.
+                clearEpollOut();
+                break;
+            }
+
+            // Do gathering write if:
+            // * the outbound buffer contains more than one messages and
+            // * they are all buffers rather than a file region.
+            if (msgCount > 1) {
+                // Ensure the pending writes are made of ByteBufs only.
+                ByteBuffer[] nioBuffers = in.nioBuffers();
+                if (nioBuffers != null) {
+                    writeBytesMultiple(in, msgCount, nioBuffers);
+
+                    // We do not break the loop here even if the outbound buffer was flushed completely,
+                    // because a user might have triggered another write and flush when we notify his or her
+                    // listeners.
                     continue;
                 }
             }
 
+            // The outbound buffer contains only one message or it contains a file region.
             Object msg = in.current();
             if (msg instanceof ByteBuf) {
                 ByteBuf buf = (ByteBuf) msg;