From 2b51a78e96091d06203d6febe96af359b248bae5 Mon Sep 17 00:00:00 2001
From: Aikar <aikar@aikar.co>
Date: Thu, 3 Mar 2016 01:17:12 -0600
Subject: [PATCH] Ensure commands are not ran async

Plugins calling Player.chat("/foo") or Server.dispatchCommand() could
trigger the server to execute a command while on another thread.

These commands would then process EXPECTING to be on the main thread, leaving to
very hard to trace concurrency issues.

This change will synchronize the command execution back to the main thread, causing a
big slowdown in execution but throwing an exception at same time to raise awareness
that it is happening so that plugin authors can fix their code to stop executing commands async.

diff --git a/src/main/java/net/minecraft/server/PlayerConnection.java b/src/main/java/net/minecraft/server/PlayerConnection.java
index 0546cb8..de4df07 100644
--- a/src/main/java/net/minecraft/server/PlayerConnection.java
+++ b/src/main/java/net/minecraft/server/PlayerConnection.java
@@ -1274,6 +1274,29 @@ public class PlayerConnection implements PacketListenerPlayIn, ITickable {
         }
 
         if (!async && s.startsWith("/")) {
+            // Paper Start
+            if (!org.bukkit.Bukkit.isPrimaryThread()) {
+                final String fCommandLine = s;
+                MinecraftServer.LOGGER.log(org.apache.logging.log4j.Level.ERROR, "Command Dispatched Async: " + fCommandLine);
+                MinecraftServer.LOGGER.log(org.apache.logging.log4j.Level.ERROR, "Please notify author of plugin causing this execution to fix this bug! see: http://bit.ly/1oSiM6C", new Throwable());
+                Waitable wait = new Waitable() {
+                    @Override
+                    protected Object evaluate() {
+                        chat(fCommandLine, false);
+                        return null;
+                    }
+                };
+                minecraftServer.processQueue.add(wait);
+                try {
+                    wait.get();
+                    return;
+                } catch (InterruptedException e) {
+                    Thread.currentThread().interrupt(); // This is proper habit for java. If we aren't handling it, pass it on!
+                } catch (Exception e) {
+                    throw new RuntimeException("Exception processing chat command", e.getCause());
+                }
+            }
+            // Paper End
             this.handleCommand(s);
         } else if (this.player.getChatFlags() == EntityHuman.EnumChatVisibility.SYSTEM) {
             // Do nothing, this is coming from a plugin
diff --git a/src/main/java/org/bukkit/craftbukkit/CraftServer.java b/src/main/java/org/bukkit/craftbukkit/CraftServer.java
index b5132cd..8e501b6 100644
--- a/src/main/java/org/bukkit/craftbukkit/CraftServer.java
+++ b/src/main/java/org/bukkit/craftbukkit/CraftServer.java
@@ -644,6 +644,29 @@ public final class CraftServer implements Server {
         Validate.notNull(sender, "Sender cannot be null");
         Validate.notNull(commandLine, "CommandLine cannot be null");
 
+        // Paper Start
+        if (!Bukkit.isPrimaryThread()) {
+            final CommandSender fSender = sender;
+            final String fCommandLine = commandLine;
+            Bukkit.getLogger().log(Level.SEVERE, "Command Dispatched Async: " + commandLine);
+            Bukkit.getLogger().log(Level.SEVERE, "Please notify author of plugin causing this execution to fix this bug! see: http://bit.ly/1oSiM6C", new Throwable());
+            org.bukkit.craftbukkit.util.Waitable<Boolean> wait = new org.bukkit.craftbukkit.util.Waitable<Boolean>() {
+                @Override
+                protected Boolean evaluate() {
+                    return dispatchCommand(fSender, fCommandLine);
+                }
+            };
+            net.minecraft.server.MinecraftServer.getServer().processQueue.add(wait);
+            try {
+                return wait.get();
+            } catch (InterruptedException e) {
+                Thread.currentThread().interrupt(); // This is proper habit for java. If we aren't handling it, pass it on!
+            } catch (Exception e) {
+                throw new RuntimeException("Exception processing dispatch command", e.getCause());
+            }
+        }
+        // Paper End
+
         if (commandMap.dispatch(sender, commandLine)) {
             return true;
         }
-- 
2.9.3