Windows Crash (Bun Segfault)

Danger

PizzaPi’s compiled Windows binary can crash with a segmentation fault shortly after starting. This is a known upstream bug in the Bun runtime, not a PizzaPi bug. It affects all applications that ship compiled Bun binaries on Windows.

Symptoms

The runner starts, connects to the relay, registers successfully, then crashes:

pizzapi runner: connecting to relay at https://example.com/runner…
pizzapi runner: connected. Registering as 9c0174ad-…
pizzapi runner: registered as 9c0174ad-…

panic(thread 41472): Segmentation fault at address 0x3C
oh no: Bun has crashed. This indicates a bug in Bun, not your code.

The crash address varies — common values include 0x3C, 0x18, 0x0, 0x30, and 0xFFFFFFFFFFFFFFFF. The crash may happen on a worker thread (not the main thread). It is non-deterministic — sometimes the runner works fine for hours, other times it crashes within seconds.

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Root Cause

The crash is caused by a JavaScriptCore (JSC) garbage collector use-after-free bug in Bun’s Windows builds. Specifically:

• Object finalizers fail to clear WriteBarrier fields before destroying objects
• The GC then accesses freed memory during sweep/marking phases
• This causes a segmentation fault at a small offset from a null/freed pointer

Three distinct crash families have been identified:

Family	Thread	Addresses	Trigger
Worker Thread Cleanup	Non-main	0x3C, 0x18, 0x108	Worker/thread shutdown races
GC Sweep Finalizer	Main or worker	0x0, 0x4, 0x30	ShellInterpreter finalizer bug
Heap Corruption	Main	0xFFFFFFFFFFFFFFFF	Double-free during Worker/VM destruction

Why PizzaPi Is Especially Affected

The runner daemon hits multiple known triggers:

• Long-lived process — runs continuously
• child_process.spawn() — spawns worker subprocesses for each session
• WebSocket threads — Socket.IO background I/O
• fetch() calls — usage cache refresh on background threads
• Compiled standalone binary — bun build --compile binaries are more affected than bun run

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Affected Versions

Every tested Bun version on Windows crashes: v1.2.18, v1.2.21, v1.3.0, v1.3.5, v1.3.6, v1.3.8, v1.3.9-canary, and v1.3.10.

Bun v1.3.10 (the latest release as of February 2026) shipped several GC safety fixes that reduced crash frequency, but did not fully resolve the issue — crashes are still reported on v1.3.10.

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Workarounds

1. Use WSL2 (Recommended)

The bug is Windows-specific. Running the runner inside WSL2 avoids it entirely:

wsl

# Inside WSL2:
pizza runner

Tip

WSL2 is the most reliable workaround. The Linux Bun binary does not have this crash.

2. Run from Source with Bun Runtime

Compiled standalone executables crash more frequently than bun run. If you have Bun installed on Windows, you can run from source:

# Install Bun for Windows
powershell -c "irm bun.sh/install.ps1 | iex"

# Clone and run from source
git clone https://github.com/badlogic/PizzaPi.git
cd PizzaPi
bun install
bun run build
bun packages/cli/src/index.ts runner

3. Retry

The crash is a race condition — non-deterministic. Simply restarting often works:

pizza runner

The supervisor process automatically restarts the daemon on crash, so the runner may recover on its own.

4. Remove .env Files

One confirmed trigger is standalone executables crashing when a .env file exists in the working directory. The dotenv loader mutates environment state across threads. Try removing or renaming any .env file in the directory where you run the runner.

5. Use a Linux or macOS Machine

If you have access to a Linux or macOS machine (including a cloud VM), run the runner there instead. The crash is Windows-specific.

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Upstream Tracking

This is tracked across multiple GitHub issues:

Bun Runtime Issues (oven-sh/bun)

Issue	Description
#18198	Original worker thread segfault after exit
#23177	ShellInterpreter finalizer GC use-after-free (root cause identified)
#23470	Crash during bun build --compile
#23904	Compiled exe crash at 0xFFFFFFFFFFFFFFFF
#26026	Bun v1.3.5 segfault on Windows 10 x64
#26625	GC finalizer crash persists in v1.3.8
#26853	Segfault 0xFFFFFFFFFFFFFFFF on Windows x64 canary
#27414	Bun v1.3.10 still crashing on Windows (Feb 2026)

Embedder Reports (Other Projects Experiencing Same Bug)

Issue	Description
claude-code#21875	78 crashes documented, 3 crash families catalogued
claude-code#27003	Confirms v1.3.10 fix is incomplete

Bun Release Notes

• Bun v1.3.10 blog post — Lists GC safety fixes and Windows-specific crash fixes (partial)

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When Will This Be Fixed?

The Bun team is aware of the issue and has been shipping incremental fixes. The v1.3.10 release addressed several crash variants but the underlying JSC GC use-after-free on Windows is not fully resolved. We will update the bundled Bun version when a complete fix ships.

In the meantime, WSL2 is the recommended way to run PizzaPi on a Windows machine.