SpigotMC#3392: Consolidate flushes to reduce syscalls, improves performance

Based on Netty FlushConsolidationHandler

Author: Janmm14

proxy/src/main/java/net/md_5/bungee/ServerConnector.java

@@ -327,7 +327,7 @@ public void handle(Login login) throws Exception
         user.setServer( server );
         ch.getHandle().pipeline().get( HandlerBoss.class ).setHandler( new DownstreamBridge( bungee, user, server ) );
 
-        // Updates the flush handler connections, the methods add the handler if needed
+        // Updates the flush handler connections (the get/set methods add the channel handlers if needed)
         ch.setFlushSignalingTarget( user.getCh().getFlushConsolidationHandler( false ) );
         user.getCh().setFlushSignalingTarget( ch.getFlushConsolidationHandler( true ) );
 

proxy/src/main/java/net/md_5/bungee/UserConnection.java

@@ -21,6 +21,7 @@
 import java.util.Queue;
 import java.util.UUID;
 import java.util.logging.Level;
+import lombok.AccessLevel;
 import lombok.Getter;
 import lombok.NonNull;
 import lombok.RequiredArgsConstructor;
@@ -72,7 +73,7 @@ public final class UserConnection implements ProxiedPlayer
     /*========================================================================*/
     @NonNull
     private final ProxyServer bungee;
-    @Getter
+    @Getter(AccessLevel.PACKAGE)
     @NonNull
     private final ChannelWrapper ch;
     @Getter

proxy/src/main/java/net/md_5/bungee/netty/ChannelWrapper.java

@@ -49,16 +49,27 @@ public void setVersion(int protocol)
         ch.pipeline().get( MinecraftEncoder.class ).setProtocolVersion( protocol );
     }
 
+    /**
+     * Set the {@link FlushSignalingHandler} target. If the handler is absent, one will be added.
+     * @param target the (new) target for the flush signaling handler
+     */
     public void setFlushSignalingTarget(BungeeFlushConsolidationHandler target)
     {
         FlushSignalingHandler handler = ch.pipeline().get( FlushSignalingHandler.class );
         if ( handler == null )
         {
-            ch.pipeline().addFirst( PipelineUtils.FLUSH_SIGNALING, handler = new FlushSignalingHandler( target ) );
+            ch.pipeline().addFirst( PipelineUtils.FLUSH_SIGNALING, new FlushSignalingHandler( target ) );
+        } else
+        {
+            handler.setTarget( target );
         }
-        handler.setTarget( target );
     }
 
+    /**
+     * Get the flush consolidation handler of this channel. If none is present, one will be added.
+     * @param toClient whether this channel is a bungee-client connection
+     * @return the flush consolidation handler for this channel
+     */
     public BungeeFlushConsolidationHandler getFlushConsolidationHandler(boolean toClient)
     {
         BungeeFlushConsolidationHandler handler = ch.pipeline().get( BungeeFlushConsolidationHandler.class );

proxy/src/main/java/net/md_5/bungee/netty/flush/BungeeFlushConsolidationHandler.java

@@ -84,7 +84,7 @@ public final class BungeeFlushConsolidationHandler extends ChannelDuplexHandler
     /**
      * Creates a new instance with bungee's default values
      *
-     * @param toClient whether this handler is for a client connection
+     * @param toClient whether this handler is for a bungee-client connection
      * @return a new instance of BungeeFlushConsolidationHandler
      */
     public static BungeeFlushConsolidationHandler newInstance(boolean toClient)