Server hang/deadlock if chunk load occurs in onEnable

[RoboMWM]

What behavior is expected:

no deadlock/eternal hang on server startup

What behavior is observed:

server startup hangs on either multiverse-core if keepspawninmemory is set to true, or if creativeparkour loads up (creativeparkour apparently checks/sets blocks in its world in onEnable).

Steps/models to reproduce:

• Have plugin load chunks/place blocks or something in a world that causes chunks to be loaded during onEnable
• That chunk must throw an exception when being loaded (i.e. chunk corruption, e.g. build 236, NBT issue)

Plugin list:

Let me know if you want my 100+ plugin list c:

Paper version:

[Server thread/INFO]: Starting minecraft server version 1.16.3
[Server thread/INFO]: Loading properties
[Server thread/INFO]: This server is running Paper version git-Paper-247 (MC: 1.16.3) (Implementing API version 1.16.3-R0.1-SNAPSHOT)

Anything else:

N​NY​aK​Np​Gm​s0​eU​Vp​iS​dH​z sees a hang on the chunk loading thread to print an error/crash report? - which it needs to get the plugin list - but this is locked by the server thread since it's still enabling plugins.

https://korobi.vq.lc/network/spigot/channel/paper-help/logs/2020/10/26/#L3187

jstack of the relevant threads:

CreativeParkour: https://gist.github.com/RoboMWM/beef47af98a91cba37685c0ba1d8f340
Multiverse: https://gist.github.com/RoboMWM/7c3f90181e11691129b721acef4e0187
RotatoR: https://gist.github.com/RoboMWM/edd98642e0886efa66f6f65e9421fa64

[aikar]

Yeah it sucks but this will never be fixed unless someone wants to come up with some extreme hack that doesn't suck.

[RoboMWM]

I'm not even sure what NBT issue I'd even have with these worlds, haven't had this issue until a week or so ago when I noticed this server wasn't starting - and is happening to any world.

[RoboMWM]

Removed/disabled all functions that cause chunk loads (setting keepSpawnInMemory in another plugin, etc.) and the server has started with no NBT issues or other crashes that I can see in the log. Unless I'm not looking for NBT issues properly, my guess is any plugin that loads chunks in onEnable is toast?

Edit: Mk I see the NBT issues now when joining the server and visiting the worlds. Not sure how this happened to every single chunk that's normally loaded on start was due to the build 236 issue.

[aikar]

No, only for a bad chunk. the server was trying to generate a crash report, and that's what lead to the deadlock.

main thread holds lock, chunk threads detect a fatal crash and tries to gen a crash report. crash report then wants to include the plugins in said report.

Only option here would be if crash reports checked that the server had finished starting already and DIDN'T include plugins, OR the plugins is cached in a way it no longer needs that same lock.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.