fix(jsc): fix data race on VirtualMachine::is_shutting_down

[DagmawiKK]

What does this PR do?

Fixes a data race on VirtualMachine::is_shutting_down.

is_shutting_down was a plain bool, written from the main JS thread and read from the HTTP background thread via &'static VirtualMachine. Under the Rust memory model this is undefined behavior. On ARM, the write may never propagate to the reading core without an atomic barrier, causing the HTTP thread to operate on JSC state (global_this, JSPromiseStrong) after the VM has begun destructing in global_exit().

The fix changes the field to AtomicBool:

• Reads: load(Ordering::Acquire) guarantees that seeing true synchronizes-with the release store, making all prior teardown writes visible
• Writes: store(true, Ordering::Release) prevents reordering of cleanup hooks past the flag

How did you verify your code works?

• Build succeeds (bun run build) with no new warnings
• bun bd test test/js/bun/http/serve.test.ts -t "should work" — 11 pass, 0 fail

[claude]

Claude Code Review

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[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

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📥 Commits

Reviewing files that changed from the base of the PR and between 172afa5 and 430c6d0.

📒 Files selected for processing (3)

• src/jsc/VirtualMachine.rs
• src/jsc/web_worker.rs
• src/runtime/cli/test_command.rs

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Walkthrough

This PR converts the VirtualMachine.is_shutting_down shutdown flag from a plain bool to an AtomicBool. All read operations now use Ordering::Acquire and all write operations use Ordering::Release to ensure proper cross-thread synchronization semantics during VM shutdown across multiple code paths.

Changes

Atomic shutdown flag synchronization

Layer / File(s)	Summary
Atomic shutdown contract and readers src/jsc/VirtualMachine.rs	VirtualMachine.is_shutting_down field type changes from bool to AtomicBool. The is_shutting_down() accessor and script_execution_status() branch now perform Ordering::Acquire reads on the atomic field.
Shutdown flag writers across exit paths src/jsc/VirtualMachine.rs, src/jsc/web_worker.rs, src/runtime/cli/test_command.rs	All shutdown signaling sites (global_exit(), WebWorker::shutdown(), and test command error paths) update the flag using store(true, Ordering::Release) instead of direct assignment, ensuring visibility to other threads.

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately and concisely describes the main change: fixing a data race on VirtualMachine::is_shutting_down by converting it to AtomicBool.
Description check	✅ Passed	The description covers both required template sections with detailed technical explanation of the data race issue, the fix implementation, and verification steps.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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