Paper/patches/server/0701-Allow-controlled-flushing-for-network-manager.patch

From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Spottedleaf <Spottedleaf@users.noreply.github.com>
Date: Sat, 4 Apr 2020 15:27:44 -0700
Subject: [PATCH] Allow controlled flushing for network manager

Only make one flush call when emptying the packet queue too

This patch will be used to optimise out flush calls in later
patches.

diff --git a/src/main/java/net/minecraft/network/Connection.java b/src/main/java/net/minecraft/network/Connection.java
index 9042f2953b1cf21969faf33883d3c845553e937e..3355d0d75675e2f9a62c4681871ba0f403073286 100644
--- a/src/main/java/net/minecraft/network/Connection.java
+++ b/src/main/java/net/minecraft/network/Connection.java
@@ -122,6 +122,39 @@ public class Connection extends SimpleChannelInboundHandler<Packet<?>> {
     public ConnectionProtocol protocol;
     // Paper end
 
+    // Paper start - allow controlled flushing
+    volatile boolean canFlush = true;
+    private final java.util.concurrent.atomic.AtomicInteger packetWrites = new java.util.concurrent.atomic.AtomicInteger();
+    private int flushPacketsStart;
+    private final Object flushLock = new Object();
+
+    public void disableAutomaticFlush() {
+        synchronized (this.flushLock) {
+            this.flushPacketsStart = this.packetWrites.get(); // must be volatile and before canFlush = false
+            this.canFlush = false;
+        }
+    }
+
+    public void enableAutomaticFlush() {
+        synchronized (this.flushLock) {
+            this.canFlush = true;
+            if (this.packetWrites.get() != this.flushPacketsStart) { // must be after canFlush = true
+                this.flush(); // only make the flush call if we need to
+            }
+        }
+    }
+
+    private final void flush() {
+        if (this.channel.eventLoop().inEventLoop()) {
+            this.channel.flush();
+        } else {
+            this.channel.eventLoop().execute(() -> {
+                this.channel.flush();
+            });
+        }
+    }
+    // Paper end - allow controlled flushing
+
     public Connection(PacketFlow side) {
         this.receiving = side;
     }
@@ -286,7 +319,7 @@ public class Connection extends SimpleChannelInboundHandler<Packet<?>> {
             io.papermc.paper.util.MCUtil.isMainThread() && packet.isReady() && this.queue.isEmpty() &&
             (packet.getExtraPackets() == null || packet.getExtraPackets().isEmpty())
         ))) {
-            this.sendPacket(packet, callbacks);
+            this.sendPacket(packet, callbacks, null); // Paper
             return;
         }
         // write the packets to the queue, then flush - antixray hooks there already
@@ -310,6 +343,14 @@ public class Connection extends SimpleChannelInboundHandler<Packet<?>> {
     }
 
     private void sendPacket(Packet<?> packet, @Nullable PacketSendListener callbacks) {
+        // Paper start - add flush parameter
+        this.sendPacket(packet, callbacks, Boolean.TRUE);
+    }
+    private void sendPacket(Packet<?> packet, @Nullable PacketSendListener callbacks, Boolean flushConditional) {
+        this.packetWrites.getAndIncrement(); // must be befeore using canFlush
+        boolean effectiveFlush = flushConditional == null ? this.canFlush : flushConditional.booleanValue();
+        final boolean flush = effectiveFlush || packet instanceof net.minecraft.network.protocol.game.ClientboundKeepAlivePacket || packet instanceof ClientboundDisconnectPacket; // no delay for certain packets
+        // Paper end - add flush parameter
         ConnectionProtocol enumprotocol = ConnectionProtocol.getProtocolForPacket(packet);
         ConnectionProtocol enumprotocol1 = this.getCurrentProtocol();
 
@@ -320,16 +361,21 @@ public class Connection extends SimpleChannelInboundHandler<Packet<?>> {
         }
 
         if (this.channel.eventLoop().inEventLoop()) {
-            this.doSendPacket(packet, callbacks, enumprotocol, enumprotocol1);
+            this.doSendPacket(packet, callbacks, enumprotocol, enumprotocol1, flush); // Paper
         } else {
             this.channel.eventLoop().execute(() -> {
-                this.doSendPacket(packet, callbacks, enumprotocol, enumprotocol1);
+                this.doSendPacket(packet, callbacks, enumprotocol, enumprotocol1, flush); // Paper
             });
         }
 
     }
 
     private void doSendPacket(Packet<?> packet, @Nullable PacketSendListener callbacks, ConnectionProtocol packetState, ConnectionProtocol currentState) {
+        // Paper start - add flush parameter
+        this.doSendPacket(packet, callbacks, packetState, currentState, true);
+    }
+    private void doSendPacket(Packet<?> packet, @Nullable PacketSendListener callbacks, ConnectionProtocol packetState, ConnectionProtocol currentState, boolean flush) {
+        // Paper end - add flush parameter
         if (packetState != currentState) {
             this.setProtocol(packetState);
         }
@@ -343,7 +389,7 @@ public class Connection extends SimpleChannelInboundHandler<Packet<?>> {
 
         try {
             // Paper end
-        ChannelFuture channelfuture = this.channel.writeAndFlush(packet);
+        ChannelFuture channelfuture = flush ? this.channel.writeAndFlush(packet) : this.channel.write(packet); // Paper - add flush parameter
 
         if (callbacks != null) {
             channelfuture.addListener((future) -> {
@@ -399,6 +445,10 @@ public class Connection extends SimpleChannelInboundHandler<Packet<?>> {
     private boolean processQueue() {
         try { // Paper - add pending task queue
         if (this.queue.isEmpty()) return true;
+        // Paper start - make only one flush call per sendPacketQueue() call
+        final boolean needsFlush = this.canFlush;
+        boolean hasWrotePacket = false;
+        // Paper end - make only one flush call per sendPacketQueue() call
         // If we are on main, we are safe here in that nothing else should be processing queue off main anymore
         // But if we are not on main due to login/status, the parent is synchronized on packetQueue
         java.util.Iterator<PacketHolder> iterator = this.queue.iterator();
@@ -406,7 +456,7 @@ public class Connection extends SimpleChannelInboundHandler<Packet<?>> {
             PacketHolder queued = iterator.next(); // poll -> peek
 
             // Fix NPE (Spigot bug caused by handleDisconnection())
-            if (queued == null) {
+            if (false && queued == null) { // Paper - diff on change, this logic is redundant: iterator guarantees ret of an element - on change, hook the flush logic here
                 return true;
             }
 
@@ -418,11 +468,17 @@ public class Connection extends SimpleChannelInboundHandler<Packet<?>> {
 
             Packet<?> packet = queued.packet;
             if (!packet.isReady()) {
+                // Paper start - make only one flush call per sendPacketQueue() call
+                if (hasWrotePacket && (needsFlush || this.canFlush)) {
+                    this.flush();
+                }
+                // Paper end - make only one flush call per sendPacketQueue() call
                 return false;
             } else {
                 iterator.remove();
                 if (queued.tryMarkConsumed()) { // Paper - try to mark isConsumed flag for de-duplicating packet
-                    this.sendPacket(packet, queued.listener);
+                    this.sendPacket(packet, queued.listener, (!iterator.hasNext() && (needsFlush || this.canFlush)) ? Boolean.TRUE : Boolean.FALSE); // Paper - make only one flush call per sendPacketQueue() call
+                    hasWrotePacket = true; // Paper - make only one flush call per sendPacketQueue() call
                 }
             }
         }