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Paper/patches/server/0414-Fix-Chunk-Post-Processing-deadlock-risk.patch
MiniDigger 4104545b11 remove system property for book size limits
"It was from a different time before books were as jank as they are now. As time has gone on they've only proven to be worse and worse."
2021-06-17 21:12:40 +02:00

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From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Aikar <aikar@aikar.co>
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 538bb603b1a516f33bbe8c4e1974efc902c4bc85..7ef52d0ae501312590802acb5f54fcf6f7cdac9e 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<ServerPlayer> pooledLinkedPlayerHashSets = new com.destroystokyo.paper.util.misc.PooledLinkedHashSets<>();
// Paper start - no-tick view distance
@@ -1090,7 +1091,7 @@ 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 0c76218134bdf8d80e3680227934ff5f70c26df2..0bb931ae8faa8e1fe36895d8321a9b36d325c3ed 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