1 files changed, 48 insertions, 0 deletions
diff --git a/patches/server/0411-Allow-multiple-callbacks-to-schedule-for-Callback-Ex.patch b/patches/server/0411-Allow-multiple-callbacks-to-schedule-for-Callback-Ex.patch
new file mode 100644
index 0000000000..1ad36331ec
--- /dev/null
+++ b/patches/server/0411-Allow-multiple-callbacks-to-schedule-for-Callback-Ex.patch
@@ -0,0 +1,48 @@
+From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
+From: Aikar <[email protected]>
+Date: Tue, 21 Apr 2020 03:51:53 -0400
+Subject: [PATCH] Allow multiple callbacks to schedule for Callback Executor
+
+ChunkMapDistance polls multiple entries for pendingChunkUpdates
+
+Each of these have the potential to move a chunk in and out of
+"Loaded" state, which will result in multiple callbacks being
+needed within a single tick of ChunkMapDistance
+
+Use an ArrayDeque to store this Queue
+
+We make sure to also implement a pattern that is recursion safe too.
+
+diff --git a/src/main/java/net/minecraft/server/level/ChunkMap.java b/src/main/java/net/minecraft/server/level/ChunkMap.java
+index 2cb807f7095648948527b5b9151770193970cc00..7fa35cba408d036e649e6d63bace88e6047c02b4 100644
+--- a/src/main/java/net/minecraft/server/level/ChunkMap.java
++++ b/src/main/java/net/minecraft/server/level/ChunkMap.java
+@@ -172,15 +172,27 @@ public class ChunkMap extends ChunkStorage implements ChunkHolder.PlayerProvider
+     public final CallbackExecutor callbackExecutor = new CallbackExecutor();
+     public static final class CallbackExecutor implements java.util.concurrent.Executor, Runnable {
+ 
+-        private final java.util.Queue<Runnable> queue = new java.util.ArrayDeque<>();
++        // Paper start - replace impl with recursive safe multi entry queue
++        // it's possible to schedule multiple tasks currently, so it's vital we change this impl
++        // If we recurse into the executor again, we will append to another queue, ensuring task order consistency
++        private java.util.Queue<Runnable> queue = new java.util.ArrayDeque<>(); // Paper - remove final
+ 
+         @Override
+         public void execute(Runnable runnable) {
++            if (this.queue == null) {
++                this.queue = new java.util.ArrayDeque<>();
++            }
+             this.queue.add(runnable);
+         }
+ 
+         @Override
+         public void run() {
++            if (this.queue == null) {
++                return;
++            }
++            java.util.Queue<Runnable> queue = this.queue;
++            this.queue = null;
++            // Paper end
+             Runnable task;
+             while ((task = this.queue.poll()) != null) {
+                 task.run();