Avoid twice thread check for #13 w/ Fixes double player updating

sources/src/main/java/io/akarin/server/core/AkarinSlackScheduler.java

@@ -42,6 +42,7 @@ public class AkarinSlackScheduler extends Thread {
         
         while (server.isRunning()) {
             // Send time updates to everyone, it will get the right time from the world the player is in.
+            // Time update, from MinecraftServer#D
             if (++updateTime >= AkarinGlobalConfig.timeUpdateInterval) {
                 for (EntityPlayer player : server.getPlayerList().players) {
                     player.playerConnection.sendPacket(new PacketPlayOutUpdateTime(player.world.getTime(), player.getPlayerTime(), player.world.getGameRules().getBoolean("doDaylightCycle"))); // Add support for per player time
@@ -49,6 +50,7 @@ public class AkarinSlackScheduler extends Thread {
                 updateTime = 0;
             }
             
+            // Keep alive, from PlayerConnection#e
             for (EntityPlayer player : server.getPlayerList().players) {
                 PlayerConnection conn = player.playerConnection;
                 // Paper - give clients a longer time to respond to pings as per pre 1.12.2 timings
@@ -73,12 +75,14 @@ public class AkarinSlackScheduler extends Thread {
                 }
             }
             
+            // Force hardcore difficulty, from WorldServer#doTick
             for (WorldServer world : server.worlds) {
                 if (world.getWorldData().isHardcore() && world.getDifficulty() != EnumDifficulty.HARD) {
                     world.getWorldData().setDifficulty(EnumDifficulty.HARD);
                 }
             }
             
+            // Update player info, from PlayerList#tick
             if (++resendPlayersInfo > AkarinGlobalConfig.playersInfoUpdateInterval) {
                 for (EntityPlayer target : server.getPlayerList().players) {
                     target.playerConnection.sendPacket(new PacketPlayOutPlayerInfo(PacketPlayOutPlayerInfo.EnumPlayerInfoAction.UPDATE_LATENCY, Iterables.filter(server.getPlayerList().players, new Predicate<EntityPlayer>() {

sources/src/main/java/io/akarin/server/mixin/core/MixinMinecraftServer.java

@@ -175,10 +175,6 @@ public abstract class MixinMinecraftServer {
     @Overwrite
     public void D() throws InterruptedException {
         Runnable runnable;
-        Akari.callbackTiming.startTiming();
-        while ((runnable = Akari.callbackQueue.poll()) != null) runnable.run();
-        Akari.callbackTiming.stopTiming();
-        
         MinecraftTimings.bukkitSchedulerTimer.startTiming();
         this.server.getScheduler().mainThreadHeartbeat(this.ticks);
         MinecraftTimings.bukkitSchedulerTimer.stopTiming();
@@ -251,6 +247,10 @@ public abstract class MixinMinecraftServer {
         serverConnection().c();
         MinecraftTimings.connectionTimer.stopTiming();
         
+        Akari.callbackTiming.startTiming();
+        while ((runnable = Akari.callbackQueue.poll()) != null) runnable.run();
+        Akari.callbackTiming.stopTiming();
+        
         MinecraftTimings.commandFunctionsTimer.startTiming();
         functionManager().e();
         MinecraftTimings.commandFunctionsTimer.stopTiming();

sources/src/main/java/io/akarin/server/mixin/core/MixinPlayerConnectionUtils.java

@@ -0,0 +1,29 @@
+package io.akarin.server.mixin.core;
+
+import org.spongepowered.asm.mixin.Mixin;
+import org.spongepowered.asm.mixin.Overwrite;
+import co.aikar.timings.MinecraftTimings;
+import co.aikar.timings.Timing;
+import io.akarin.api.internal.Akari;
+import net.minecraft.server.CancelledPacketHandleException;
+import net.minecraft.server.IAsyncTaskHandler;
+import net.minecraft.server.Packet;
+import net.minecraft.server.PacketListener;
+import net.minecraft.server.PlayerConnectionUtils;
+
+@Mixin(value = PlayerConnectionUtils.class, remap = false)
+public abstract class MixinPlayerConnectionUtils {
+    @Overwrite
+    public static <T extends PacketListener> void ensureMainThread(final Packet<T> packet, final T listener, IAsyncTaskHandler iasynctaskhandler) throws CancelledPacketHandleException {
+        if (!iasynctaskhandler.isMainThread()) {
+            Timing timing = MinecraftTimings.getPacketTiming(packet);
+            // MinecraftServer#postToMainThread inlined thread check, no twice
+            Akari.callbackQueue.add(() -> {
+                try (Timing ignored = timing.startTiming()) {
+                    packet.a(listener);
+                }
+            });
+            throw CancelledPacketHandleException.INSTANCE;
+        }
+    }
+}

sources/src/main/java/io/akarin/server/mixin/core/MixinPlayerList.java

@@ -0,0 +1,12 @@
+package io.akarin.server.mixin.core;
+
+import org.spongepowered.asm.mixin.Mixin;
+import org.spongepowered.asm.mixin.Overwrite;
+
+import net.minecraft.server.PlayerList;
+
+@Mixin(value = PlayerList.class, remap = false)
+public abstract class MixinPlayerList {
+    @Overwrite
+    public void tick() {} // Migrated to slack service
+}

sources/src/main/resources/mixins.akarin.core.json

@@ -15,6 +15,7 @@
         
         "core.MixinWorld",
         "core.MixinMCUtil",
+        "core.MixinPlayerList",
         "core.MixinCommandBan",
         "core.MixinCommandKick",
         "core.MixinCraftServer",
@@ -27,6 +28,7 @@
         "core.MixinVersionCommand",
         "core.MixinMinecraftServer",
         "core.MixinChunkIOExecutor",
+        "core.MixinPlayerConnectionUtils",
         
         "cps.MixinCraftWorld",
         "cps.MixinChunkProviderServer",