Threadcore

0.0.1-alpha — first public release

Minecraft 1.20.1 · Fabric · server-side · Java 17

You need two mods

Threadcore now requires Threadcore API (threadcore-api >= 0.0.2) as a separate download, the same way mods require Fabric API. Install both on the server.

The API is split out because it is Apache-2.0 — free for anyone to build against — while Threadcore itself is All Rights Reserved. One jar could not honestly state both licences.

What it does

Each world is divided into regions, and regions tick in parallel on a pool of worker threads. Entities, block entities and scheduled ticks in different regions run at the same time. Everything that must be single-threaded still is: region threads never write a block directly, never spawn or remove an entity directly, and never touch another region's chunks — those are deferred to the main thread and replayed in order.

How it avoids corrupting your world:

• Thread domains. Every operation is tagged MAIN, REGION or ASYNC and asserted at runtime. In strict mode a violation is loud, not silent.
• Deferral queues for every cross-region mutation: block changes, entity spawn/removal/position, scheduled ticks, lighting, neighbour updates, path recalculation.
• Snapshot reads — off-thread readers get a per-tick frozen view rather than a racing one.
• Probation — an entity type that misbehaves is demoted and stops being offloaded.
• An audit layer that ledgers items and XP and reports anything that does not balance.
• Compatibility refusal — where another mod's internals make offloading unsafe, Threadcore refuses to arm rather than hoping. Lithium is detected and specific hazards are declined.

Before you install

• Back up your world. Not a formality — this moves the tick loop.
• This is an alpha. The 1.20.1 build has been running a production server since 2026-09-16, which is where the confidence comes from, but your modpack is not that server.
• It is not a universal speedup. The gain depends on how much of your tick is entities and block entities spread across regions. A server bottlenecked on chunk generation, on one enormous farm in a single chunk, or on one mod's main-thread work will see little.
• Offload stays off for modded entity types until they pass probation, deliberately. A heavy modpack starts conservative and opens up as types prove themselves.
• Every risky behaviour has an off switch, and the defaults are the safe ones. -Dthreadcore.offload=false disables the parallel tick entirely and makes Threadcore a no-op — the quickest way to tell whether Threadcore is involved in a problem at all.

Reporting problems

Include your Minecraft and Fabric Loader versions, the full mod list, and the server log. If you can reproduce it, say whether it still happens with -Dthreadcore.offload=false.