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[BUG] enableAsyncSpawn can crash the server by blocking Async-Tick-Pool on sync chunk/structure loads #164

Description

@runningbird2

🐛 Describe the bug

With enableAsyncSpawn = true, the server can freeze and eventually watchdog.

In the crash reports, Async-Tick-Pool-Thread-* workers are stuck on sync chunk loads such as:

  • Sync load chunk [...] to status minecraft:structure_starts

At the same time, the main thread is blocked in Async’s entity ticking path. This looks like async spawning can block the same worker pool that async entity ticking later depends on.

Disabling async spawn (enableAsyncSpawn = false) stops this crash on my server.

🔁 Reproducibility

  • This bug is not consistently reproducible

📋 Steps to reproduce (skip if checked above)

  1. Enable enableAsyncSpawn = true
  2. Have active players with normal mob spawning/chunk activity
  3. After some time, the server may freeze and watchdog

✅ Expected behavior

Async spawning should not be able to stall the same worker pool that entity ticking depends on.

❌ Actual behavior

The server freezes, Async-Tick-Pool-Thread workers get stuck on sync chunk/structure loads, the main thread blocks waiting on Async entity ticking, and the watchdog kills the server.

🖥️ Environment

  • 🔧 Async version: 0.2.0+alpha-1.21.11
  • 🎮 Minecraft version: 1.21.11
  • ⚙️ Modloader & version: Fabric Loader 0.18.4
  • 📦 Other mods installed (if relevant): C2ME, Lithium, ScalableLux, ServerCore, VMP, Carpet, Async

📜 Logs

Crash report: https://mclo.gs/qKnuEMG

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T: BugFixType: Bug and/or bug fixes.

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