Paper/patches/server/0747-Prevent-unload-calls-removing-tickets-for-sync-loads.patch

From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Spottedleaf <spottedleaf@spottedleaf.dev>
Date: Thu, 18 Jun 2020 18:23:20 -0700
Subject: [PATCH] Prevent unload() calls removing tickets for sync loads


diff --git a/src/main/java/net/minecraft/server/level/ServerChunkCache.java b/src/main/java/net/minecraft/server/level/ServerChunkCache.java
index 74836552406743c16ef9e510ad22f7ba5520ea7f..280ca8758cbaf710c2bf357e41dd2af6e14b49bc 100644
--- a/src/main/java/net/minecraft/server/level/ServerChunkCache.java
+++ b/src/main/java/net/minecraft/server/level/ServerChunkCache.java
@@ -725,6 +725,8 @@ public class ServerChunkCache extends ChunkSource {
         return completablefuture;
     }
 
+    private long syncLoadCounter; // Paper - prevent plugin unloads from removing our ticket
+
     private CompletableFuture<Either<ChunkAccess, ChunkHolder.ChunkLoadingFailure>> getChunkFutureMainThread(int chunkX, int chunkZ, ChunkStatus leastStatus, boolean create) {
         // Paper start - add isUrgent - old sig left in place for dirty nms plugins
         return getChunkFutureMainThread(chunkX, chunkZ, leastStatus, create, false);
@@ -743,9 +745,12 @@ public class ServerChunkCache extends ChunkSource {
             ChunkHolder.FullChunkStatus currentChunkState = ChunkHolder.getFullChunkStatus(playerchunk.getTicketLevel());
             currentlyUnloading = (oldChunkState.isOrAfter(ChunkHolder.FullChunkStatus.BORDER) && !currentChunkState.isOrAfter(ChunkHolder.FullChunkStatus.BORDER));
         }
+        final Long identifier; // Paper - prevent plugin unloads from removing our ticket
         if (create && !currentlyUnloading) {
             // CraftBukkit end
             this.distanceManager.addTicket(TicketType.UNKNOWN, chunkcoordintpair, l, chunkcoordintpair);
+            identifier = Long.valueOf(this.syncLoadCounter++); // Paper - prevent plugin unloads from removing our ticket
+            this.distanceManager.addTicketAtLevel(TicketType.REQUIRED_LOAD, chunkcoordintpair, l, identifier); // Paper - prevent plugin unloads from removing our ticket
             if (isUrgent) this.distanceManager.markUrgent(chunkcoordintpair); // Paper - Chunk priority
             if (this.chunkAbsent(playerchunk, l)) {
                 ProfilerFiller gameprofilerfiller = this.level.getProfiler();
@@ -756,13 +761,21 @@ public class ServerChunkCache extends ChunkSource {
                 playerchunk = this.getVisibleChunkIfPresent(k);
                 gameprofilerfiller.pop();
                 if (this.chunkAbsent(playerchunk, l)) {
+                    this.distanceManager.removeTicketAtLevel(TicketType.REQUIRED_LOAD, chunkcoordintpair, l, identifier); // Paper
                     throw (IllegalStateException) Util.pauseInIde(new IllegalStateException("No chunk holder after ticket has been added"));
                 }
             }
-        }
 
+        } else { identifier = null; } // Paper - prevent plugin unloads from removing our ticket
         // Paper start - Chunk priority
         CompletableFuture<Either<ChunkAccess, ChunkHolder.ChunkLoadingFailure>> future = this.chunkAbsent(playerchunk, l) ? ChunkHolder.UNLOADED_CHUNK_FUTURE : playerchunk.getOrScheduleFuture(leastStatus, this.chunkMap);
+        // Paper start - prevent plugin unloads from removing our ticket
+        if (create && !currentlyUnloading) {
+            future.thenAcceptAsync((either) -> {
+                ServerChunkCache.this.distanceManager.removeTicketAtLevel(TicketType.REQUIRED_LOAD, chunkcoordintpair, l, identifier);
+            }, ServerChunkCache.this.mainThreadProcessor);
+        }
+        // Paper end - prevent plugin unloads from removing our ticket
         if (isUrgent) {
             future.thenAccept(either -> this.distanceManager.clearUrgent(chunkcoordintpair));
         }
diff --git a/src/main/java/net/minecraft/server/level/TicketType.java b/src/main/java/net/minecraft/server/level/TicketType.java
index 3c1698ba0d3bc412ab957777d9b5211dbc555208..41ddcf6775f99c56cf4b13b284420061e5dd6bdc 100644
--- a/src/main/java/net/minecraft/server/level/TicketType.java
+++ b/src/main/java/net/minecraft/server/level/TicketType.java
@@ -31,6 +31,7 @@ public class TicketType<T> {
     public static final TicketType<Unit> PLUGIN = TicketType.create("plugin", (a, b) -> 0); // CraftBukkit
     public static final TicketType<org.bukkit.plugin.Plugin> PLUGIN_TICKET = TicketType.create("plugin_ticket", (plugin1, plugin2) -> plugin1.getClass().getName().compareTo(plugin2.getClass().getName())); // CraftBukkit
     public static final TicketType<Long> DELAY_UNLOAD = create("delay_unload", Long::compareTo, 300); // Paper
+    public static final TicketType<Long> REQUIRED_LOAD = create("required_load", Long::compareTo); // Paper - make sure getChunkAt does not fail
 
     public static <T> TicketType<T> create(String name, Comparator<T> argumentComparator) {
         return new TicketType<>(name, argumentComparator, 0L);