From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Aikar <aikar@aikar.co>
Date: Mon, 25 May 2020 11:02:42 -0400
Subject: [PATCH] Unload leaked Cached Chunks

Due to some complexity in mojangs complicated chain of juggling
whether or not a chunk should be unloaded when the last ticket is
removed, many chunks are remaining around in the cache.

These chunks are never being targetted for unload because they are
vastly out of view distance range and have no reason to be looked at.

This is a huge issue for performance because we have to iterate these
chunks EVERY TICK... This is what's been leading to high SELF time in
Ticking Chunks timings/profiler results.

We will now detect these chunks in that iteration, and automatically
add it to the unload queue when the chunk is found without any tickets.

diff --git a/src/main/java/net/minecraft/server/ChunkProviderServer.java b/src/main/java/net/minecraft/server/ChunkProviderServer.java
index 54e89c9cc6c47ff2c4f4dd5d4c22a391f8a3d6e0..c9516d2d6724e84095e0e3c27c14870519fc05f9 100644
--- a/src/main/java/net/minecraft/server/ChunkProviderServer.java
+++ b/src/main/java/net/minecraft/server/ChunkProviderServer.java
@@ -898,6 +898,37 @@ public class ChunkProviderServer extends IChunkProvider {
                         if (chunksTicked[0]++ % 10 == 0) this.world.getMinecraftServer().midTickLoadChunks(); // Paper
                     }
                 }
+                // Paper start - remove inaccessible chunks leaked
+                else if (playerchunk.getTicketLevel() == playerchunk.oldTicketLevel &&
+                    playerChunkMap.unloadQueue.size() < 100 &&
+                    (playerchunk.lastStatusChange == 0 || world.getTime() - playerchunk.lastStatusChange > 20) &&
+                    PlayerChunk.getChunkState(playerchunk.getTicketLevel()) == PlayerChunk.State.INACCESSIBLE
+                ) {
+                    ChunkStatus chunkHolderStatus = playerchunk.getChunkHolderStatus();
+                    ChunkStatus desiredStatus = PlayerChunk.getChunkStatus(playerchunk.getTicketLevel());
+                    if (chunkHolderStatus != null && !chunkHolderStatus.isAtLeastStatus(desiredStatus)) {
+                        return;
+                    }
+
+                    if (playerchunk.lastStatusChange == 0) {
+                        playerchunk.lastStatusChange = world.getTime();
+                    } else {
+                        Chunk chunk = playerchunk.getChunk();
+                        if (chunk != null && chunk.isAnyNeighborsLoaded()) {
+                            playerchunk.lastStatusChange = world.getTime()+(20*5);
+                            return;
+                        }
+                        long key = playerchunk.location.pair();
+                        ArraySetSorted<Ticket<?>> tickets = playerChunkMap.chunkDistanceManager.tickets.get(key);
+                        if (tickets == null || tickets.isEmpty()) {
+                            playerchunk.lastStatusChange = world.getTime()+(20*30);
+                            playerChunkMap.unloadQueue.add(key);
+                        } else {
+                            playerchunk.lastStatusChange = world.getTime()+(20*5);
+                        }
+                    }
+                    // Paper end
+                }
             });
             this.world.getMethodProfiler().enter("customSpawners");
             if (flag1) {
diff --git a/src/main/java/net/minecraft/server/PlayerChunk.java b/src/main/java/net/minecraft/server/PlayerChunk.java
index b8fe42e8123e972b1ec97b048c35d90118076e66..7e4d37128738ad0ef44d14ef3b48d8c5aca0c2f5 100644
--- a/src/main/java/net/minecraft/server/PlayerChunk.java
+++ b/src/main/java/net/minecraft/server/PlayerChunk.java
@@ -44,6 +44,7 @@ public class PlayerChunk {
 
     long lastAutoSaveTime; // Paper - incremental autosave
     long inactiveTimeStart; // Paper - incremental autosave
+    long lastStatusChange; // Paper - fix chunk leak
 
     // Paper start - optimise isOutsideOfRange
     // cached here to avoid a map lookup
@@ -562,6 +563,7 @@ public class PlayerChunk {
     protected void a(PlayerChunkMap playerchunkmap) {
         ChunkStatus chunkstatus = getChunkStatus(this.oldTicketLevel);
         ChunkStatus chunkstatus1 = getChunkStatus(this.ticketLevel);
+        if (oldTicketLevel != ticketLevel) lastStatusChange = chunkMap.world.getTime(); // Paper - chunk leak
         boolean flag = this.oldTicketLevel <= PlayerChunkMap.GOLDEN_TICKET;
         boolean flag1 = this.ticketLevel <= PlayerChunkMap.GOLDEN_TICKET; // Paper - diff on change: (flag1 = new ticket level is in loadable range)
         PlayerChunk.State playerchunk_state = getChunkState(this.oldTicketLevel);