[#2577] ChannelOutboundBuffer.addFlush() unnecessary loop through all…

… entries on multiple calls

Motivation:

If ChannelOutboundBuffer.addFlush() is called multiple times and flushed != unflushed it will still loop through all entries that are not flushed yet even if it is not needed anymore as these were marked uncancellable before.

Modifications:

Check if new messages were added since addFlush() was called and only if this was the case loop through all entries and try to mark the uncancellable.

Result:

Less overhead when ChannelOuboundBuffer.addFlush() is called multiple times without new messages been added.

transport/src/main/java/io/netty/channel/ChannelOutboundBuffer.java

@@ -182,18 +182,24 @@ private void addCapacity() {
      * Mark all messages in this {@link ChannelOutboundBuffer} as flushed.
      */
     public final void addFlush() {
-        unflushed = tail;
-
-        final int mask = buffer.length - 1;
-        int i = flushed;
-        while (i != unflushed && buffer[i].msg != null) {
-            Entry entry = buffer[i];
-            if (!entry.promise.setUncancellable()) {
-                // Was cancelled so make sure we free up memory and notify about the freed bytes
-                int pending = entry.cancel();
-                decrementPendingOutboundBytes(pending);
+        // There is no need to process all entries if there was already a flush before and no new messages
+        // where added in the meantime.
+        //
+        // See https://github.com/netty/netty/issues/2577
+        if (unflushed != tail) {
+            unflushed = tail;
+
+            final int mask = buffer.length - 1;
+            int i = flushed;
+            while (i != unflushed && buffer[i].msg != null) {
+                Entry entry = buffer[i];
+                if (!entry.promise.setUncancellable()) {
+                    // Was cancelled so make sure we free up memory and notify about the freed bytes
+                    int pending = entry.cancel();
+                    decrementPendingOutboundBytes(pending);
+                }
+                i = i + 1 & mask;
             }
-            i = i + 1 & mask;
         }
     }