Paper/nms-patches/RegionFile.patch

--- a/net/minecraft/server/RegionFile.java
+++ b/net/minecraft/server/RegionFile.java
@@ -224,11 +224,11 @@
         return i < 0 || i >= 32 || j < 0 || j >= 32;
     }
 
-    private int e(int i, int j) {
+    private synchronized int e(int i, int j) { // CraftBukkit
         return this.d[i + j * 32];
     }
 
-    public boolean c(int i, int j) {
+    public boolean c(int i, int j) { // PAIL chunkExists
         return this.e(i, j) != 0;
     }