From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001 From: Aikar Date: Sat, 18 Apr 2020 04:36:11 -0400 Subject: [PATCH] Fix Chunk Post Processing deadlock risk See: https://gist.github.com/aikar/dd22bbd2a3d78a2fd3d92e95e9f28dc6 as part of post processing a chunk, we can call ChunkConverter. ChunkConverter then kicks off major physics updates, and when blocks that have connections across chunk boundries occur, a recursive risk can occur where A updates a block that triggers a physics request. That physics request may trigger a chunk request, that then enqueues a task into the Mailbox ChunkTaskQueueSorter. If anything requests that same chunk that is in the middle of conversion, it's mailbox queue is going to be held up, so the subsequent chunk request will be unable to proceed. We delay post processing of Chunk.A() 1 "pass" by re stuffing it back into the executor so that the mailbox ChunkQueue is now considered empty. This successfully fixed a reoccurring and highly reproduceable crash for heightmaps. diff --git a/src/main/java/net/minecraft/server/ChunkProviderServer.java b/src/main/java/net/minecraft/server/ChunkProviderServer.java index cc91266704043b46653bdd512637d001677ddc76..47a02737faa2eddca1b1f9063fe46afc91425169 100644 --- a/src/main/java/net/minecraft/server/ChunkProviderServer.java +++ b/src/main/java/net/minecraft/server/ChunkProviderServer.java @@ -995,6 +995,7 @@ public class ChunkProviderServer extends IChunkProvider { return super.executeNext() || execChunkTask; // Paper } } finally { + playerChunkMap.chunkLoadConversionCallbackExecutor.run(); // Paper - Add chunk load conversion callback executor to prevent deadlock due to recursion in the chunk task queue sorter playerChunkMap.callbackExecutor.run(); } // CraftBukkit end diff --git a/src/main/java/net/minecraft/server/PlayerChunkMap.java b/src/main/java/net/minecraft/server/PlayerChunkMap.java index 16e4acdb0f834883a480829a864ef7570035bc26..842f5ebad2a4d040b9912ec4841de426667cd91d 100644 --- a/src/main/java/net/minecraft/server/PlayerChunkMap.java +++ b/src/main/java/net/minecraft/server/PlayerChunkMap.java @@ -134,6 +134,8 @@ public class PlayerChunkMap extends IChunkLoader implements PlayerChunk.d { }; // CraftBukkit end + final CallbackExecutor chunkLoadConversionCallbackExecutor = new CallbackExecutor(); // Paper + // Paper start - distance maps private final com.destroystokyo.paper.util.misc.PooledLinkedHashSets pooledLinkedPlayerHashSets = new com.destroystokyo.paper.util.misc.PooledLinkedHashSets<>(); @@ -999,7 +1001,7 @@ public class PlayerChunkMap extends IChunkLoader implements PlayerChunk.d { return Either.left(chunk); }); }, (runnable) -> { - this.mailboxMain.a(ChunkTaskQueueSorter.a(playerchunk, runnable)); + this.mailboxMain.a(ChunkTaskQueueSorter.a(playerchunk, () -> PlayerChunkMap.this.chunkLoadConversionCallbackExecutor.execute(runnable))); // Paper - delay running Chunk post processing until outside of the sorter to prevent a deadlock scenario when post processing causes another chunk request. }); completablefuture1.thenAcceptAsync((either) -> {