[#2667] Write until EAGAIN in native transport and only call setEpollOut() in this case

Motivation:

In the previous fix for #2667 I did introduce a bit overhead by calling setEpollOut() too often.

Modification:

Only call setEpollOut() if really needed and remove unused code.

Result:

Less overhead when saturate network.

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

@@ -49,7 +49,6 @@ import java.util.concurrent.TimeUnit;
 public final class EpollSocketChannel extends AbstractEpollChannel implements SocketChannel {
 
     private final EpollSocketChannelConfig config;
-    private Runnable flushTask;
 
     /**
      * The future of the current connection attempt.  If not null, subsequent
@@ -110,7 +109,6 @@ public final class EpollSocketChannel extends AbstractEpollChannel implements So
             in.remove();
             return true;
         }
-        boolean setEpollOut = false;
         boolean done = false;
         long writtenBytes = 0;
         if (buf.nioBufferCount() == 1) {
@@ -128,11 +126,12 @@ public final class EpollSocketChannel extends AbstractEpollChannel implements So
                         break;
                     }
                 } else {
-                    setEpollOut = true;
+                    // Returned EAGAIN need to set EPOLLOUT
+                    setEpollOut();
                     break;
                 }
             }
-            updateOutboundBuffer(in, writtenBytes, 1, done, setEpollOut);
+            updateOutboundBuffer(in, writtenBytes, 1, done);
             return done;
         } else {
             ByteBuffer[] nioBuffers = buf.nioBuffers();
@@ -149,7 +148,6 @@ public final class EpollSocketChannel extends AbstractEpollChannel implements So
             ChannelOutboundBuffer in, int msgCount, ByteBuffer[] nioBuffers,
             int nioBufferCnt, long expectedWrittenBytes) throws IOException {
         boolean done = false;
-        boolean setEpollOut = false;
         long writtenBytes = 0;
         int offset = 0;
         int end = offset + nioBufferCnt;
@@ -159,7 +157,8 @@ public final class EpollSocketChannel extends AbstractEpollChannel implements So
 
                 long localWrittenBytes = Native.writev(fd, nioBuffers, offset, cnt);
                 if (localWrittenBytes == 0) {
-                    setEpollOut = true;
+                    // Returned EAGAIN need to set EPOLLOUT
+                    setEpollOut();
                     break loop;
                 }
                 expectedWrittenBytes -= localWrittenBytes;
@@ -172,9 +171,6 @@ public final class EpollSocketChannel extends AbstractEpollChannel implements So
                     if (bytes > localWrittenBytes) {
                         buffer.position(pos + (int) localWrittenBytes);
                         // incomplete write
-
-                        // As we use edge-triggered we need to set EPOLLOUT as otherwise we may not get notified again
-                        setEpollOut();
                         break;
                     } else {
                         offset++;
@@ -189,12 +185,12 @@ public final class EpollSocketChannel extends AbstractEpollChannel implements So
                 }
             }
         }
-        updateOutboundBuffer(in, writtenBytes, msgCount, done, setEpollOut);
+        updateOutboundBuffer(in, writtenBytes, msgCount, done);
         return done;
     }
 
     private void updateOutboundBuffer(ChannelOutboundBuffer in, long writtenBytes, int msgCount,
-                                      boolean done, boolean setEpollOut) {
+                                      boolean done) {
         if (done) {
             // Release all buffers
             for (int i = msgCount; i > 0; i --) {
@@ -224,26 +220,6 @@ public final class EpollSocketChannel extends AbstractEpollChannel implements So
                     break;
                 }
             }
-            incompleteWrite(setEpollOut);
-        }
-    }
-
-    private void incompleteWrite(boolean setEpollOut) {
-        // Did not write completely.
-        if (setEpollOut) {
-            setEpollOut();
-        } else {
-            // Schedule flush again later so other tasks can be picked up in the meantime
-            Runnable flushTask = this.flushTask;
-            if (flushTask == null) {
-                flushTask = this.flushTask = new Runnable() {
-                    @Override
-                    public void run() {
-                        unsafe().flush();
-                    }
-                };
-            }
-            eventLoop().execute(flushTask);
         }
     }
 
@@ -254,7 +230,6 @@ public final class EpollSocketChannel extends AbstractEpollChannel implements So
      * @return amount       the amount of written bytes
      */
     private boolean writeFileRegion(ChannelOutboundBuffer in, DefaultFileRegion region) throws Exception {
-        boolean setOpWrite = false;
         boolean done = false;
         long flushedAmount = 0;
 
@@ -262,7 +237,8 @@ public final class EpollSocketChannel extends AbstractEpollChannel implements So
             long expected = region.count() - region.position();
             long localFlushedAmount = Native.sendfile(fd, region, region.transfered(), expected);
             if (localFlushedAmount == 0) {
-                setOpWrite = true;
+                // Returned EAGAIN need to set EPOLLOUT
+                setEpollOut();
                 break;
             }
 
@@ -270,9 +246,6 @@ public final class EpollSocketChannel extends AbstractEpollChannel implements So
             if (region.transfered() >= region.count()) {
                 done = true;
                 break;
-            } else {
-                // As we use edge-triggered we need to set EPOLLOUT as otherwise we may not get notified again
-                setEpollOut();
             }
         }
 
@@ -280,8 +253,6 @@ public final class EpollSocketChannel extends AbstractEpollChannel implements So
 
         if (done) {
             in.remove();
-        } else {
-            incompleteWrite(setOpWrite);
         }
         return done;
     }