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/level/ChunkMap.java b/src/main/java/net/minecraft/server/level/ChunkMap.java index dbd256b7be670d30fc68ceaa9e498bf55b405b56..9e17cfcf24d3c4358e650adac45d0ade81119fc2 100644 --- a/src/main/java/net/minecraft/server/level/ChunkMap.java +++ b/src/main/java/net/minecraft/server/level/ChunkMap.java @@ -195,6 +195,7 @@ public class ChunkMap extends ChunkStorage implements ChunkHolder.PlayerProvider }; // 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<>(); // Paper start - no-tick view distance @@ -1092,7 +1093,7 @@ public class ChunkMap extends ChunkStorage implements ChunkHolder.PlayerProvider return Either.left(chunk); }); }, (runnable) -> { - this.mainThreadMailbox.tell(ChunkTaskPriorityQueueSorter.message(holder, runnable)); + this.mainThreadMailbox.tell(ChunkTaskPriorityQueueSorter.message(holder, () -> ChunkMap.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) -> { diff --git a/src/main/java/net/minecraft/server/level/ServerChunkCache.java b/src/main/java/net/minecraft/server/level/ServerChunkCache.java index b464db85829f2f97926791056b339b937e25ed03..c8c873f9e7fd1a8ea2d32f37be6d221408b7687d 100644 --- a/src/main/java/net/minecraft/server/level/ServerChunkCache.java +++ b/src/main/java/net/minecraft/server/level/ServerChunkCache.java @@ -1001,6 +1001,7 @@ public class ServerChunkCache extends ChunkSource { return super.pollTask() || execChunkTask; // Paper } } finally { + chunkMap.chunkLoadConversionCallbackExecutor.run(); // Paper - Add chunk load conversion callback executor to prevent deadlock due to recursion in the chunk task queue sorter chunkMap.callbackExecutor.run(); } // CraftBukkit end