Async Operation Catching

Catch and throw an exception when a potentially unsafe operation occurs on a thread other than the main server thread.

By: md_5 <git@md-5.net>

paper-server/src/main/java/org/spigotmc/AsyncCatcher.java

@@ -0,0 +1,17 @@
+package org.spigotmc;
+
+import net.minecraft.server.MinecraftServer;
+
+public class AsyncCatcher
+{
+
+    public static boolean enabled = true;
+
+    public static void catchOp(String reason)
+    {
+        if ( AsyncCatcher.enabled && Thread.currentThread() != MinecraftServer.getServer().serverThread )
+        {
+            throw new IllegalStateException( "Asynchronous " + reason + "!" );
+        }
+    }
+}