[robobun]

Problem

• A worker whose event loop runs dry emits process 'exit' after its parent can no longer stop it. In a listener, worker.terminate() and process.exit() do not stop script, and a throw is lost.
• Cause: WebWorker::shutdown() drops the VM's handle (src/jsc/web_worker.rs:1024) and exit_and_free sets is_shutting_down (src/jsc/VirtualMachine.rs:2424) before the listeners run.

Fix

• exit_and_free runs the 'exit' listeners, then WebWorker::unpublish(), then the rest of the exit sequence.
• Correct: process.exit(), an uncaught error, and Node already use this order.
• Verified: test/js/node/worker_threads/worker_threads.test.ts (16 new rows, 15 fail on main), test/cli/lint/js-plugins.test.ts, and the worker and process suites.
• Self-reviewed: 17 concerns raised, 13 addressed. Rejected: a stop rule for every VM (changes main-thread exit), failing rows for other PRs' gaps (theirs), a throwing capture callback (on every route), a stop lost in a nested process.emit() (also on main).

Background

• A parent stops its worker's VM only through the VmHandle that WebWorker publishes. unpublish() removes it and forbids script.
• Considered: WebWorker::exit only (one symptom of three), a dispatch in shutdown() (the flush still runs script).

Downsides

• An error in a drained worker's 'exit' listener now gives exit code 1. Node keeps the exit code (Report a loop turn's rejections before the loop-alive check, and keep the exit code when an 'exit' listener throws #42032). Node and current Bun ignore an EventTarget listener's throw there.
• After the listeners a drained worker runs no script: node:http2 over a JS Duplex flushed 1009 bytes there, now 0 (Node: 0).
• Per worker end: +26 instructions, +1 locked operation. Per main-thread exit: +14. .text: +512 bytes.

Notes

Repro (bun 1.4.3 and main 179664e against Node v26.3.0). Common first lines:

const { Worker, isMainThread, workerData } = require("node:worker_threads");
const fs = require("node:fs"); const say = s => fs.writeSync(1, s + "\n");

terminate() during the listener:

if (isMainThread) { const flag = new Int32Array(new SharedArrayBuffer(4)); const w = new Worker(__filename, { workerData: flag }); w.on("exit", c => say("parent exit " + c)); const t = setInterval(() => { if (Atomics.load(flag, 0) === 1) { clearInterval(t); say("parent: terminate()"); w.terminate(); } }, 1); }
else { process.on("exit", c => { say("L1 " + c); Atomics.store(workerData, 0, 1); const t = Date.now(); while (Date.now() - t < 3000) {} say("L1 ran to its end: the 3 s busy loop was not interrupted"); }); }

Node and this PR: L1 0, parent: terminate(), parent exit 1. Main: L1 0, parent: terminate(), L1 ran to its end: the 3 s busy loop was not interrupted, parent exit 0. With a loop that never ends, main never exits.

process.exit() in the listener:

if (isMainThread) { const w = new Worker(__filename); w.on("error", e => say("parent error " + e.message)); w.on("exit", c => say("parent exit " + c)); }
else { process.on("exit", c => { say("L1 " + c); process.exit(5); say("L1 statement after process.exit(5)"); }); process.on("exit", c => say("L2 " + c)); }

Node and this PR: L1 0, parent exit 5. Main: L1 0, L1 statement after process.exit(5), L2 0, parent exit 5.

A throw from the listener (process.on("exit", () => { throw new Error("boom"); }) in the worker): Node parent error boom, parent exit 0. This PR parent error boom, parent exit 1. Main parent exit 0.

The order. exit_and_free now does this for a worker:

1. If the worker saw a stop request, close the gate. terminate() publishes its flag before it closes the gate, and a terminated worker must run no 'exit' listener.
2. run_exit_handlers(): clear what unwound script, write profiles, emit 'exit'. The VM is still published, so process.exit() and the parent's terminate() stop a listener like any other script. dispatch_on_exit runs the emit under an exception scope and takes a termination that reaches it outside script.
3. WebWorker::unpublish(): under the handle's lock, take the handle and stop it, then null the worker's VM pointer. No script runs on the VM from here.
4. forbid_script() if the parent stopped the worker, is_shutting_down = true, finish_exit() (the flushes and cleanup hooks), teardown.

The same order is reached on every path into shutdown(). A failed load with a listener registered by a preload is one of them, and it has a row. on_exit() is the same two halves in the same order for its other callers: the main thread, and a bun lint thread that keeps its engine.

Designs weighed. A fix in WebWorker::exit alone repairs process.exit() in a listener and leaves terminate() and the throw. An emit at the end of spin() covers the drained route and not a failed load. A dispatch in shutdown() ahead of the unpublish keeps the order in two functions, and the flush after the listeners still runs script on a VM that the parent cannot stop. Every worker end passes through exit_and_free.

Behaviour that changes.

• terminate() that lands while a drained worker's 'exit' listener runs now stops the listener. The worker exits 1 and the rest of the listener does not run.
• A parent with no 'error' listener on the worker now gets an unhandled 'error' event when a drained worker's 'exit' listener throws, as in Node.
• An error that an EventTarget listener throws inside a drained worker's 'exit' listener now reaches the parent, as it already does when the worker calls process.exit(). Node reports such errors from a process.nextTick callback, so it drops them once 'exit' is emitted. That difference exists on every route and on the main thread, and this PR does not change it.
• bun lint: a thread that frees its engine (exit_and_free has this second caller) now prints a plugin 'exit' listener's throw, like a thread that keeps its engine. The exit code does not change.
• A failed load stays the worker's only 'error' when an 'exit' listener throws.

Exit code after a throw. Node's worker fatal handler sets exit code 1 only if (!process._exiting), so a throw from an 'exit' listener keeps 0 or the assigned code. An earlier version of this change gated the two stores in uncaught_exception in the same way. The gate regressed a worker that dies of an unhandled rejection and whose 'exit' listener throws (exit 1 on Node and main, 0 with the gate), because that route does not set the code before the listeners run. #42032 adds the gate for every route and #45575 sets the code in the worker's fatal hook, so this PR leaves the rule to them. Three rows assert exit code 1 after a throw. They change to the code in effect when that rule lands.

Not tested. A terminate() that races the end of the loop has no deterministic test. No row depends on the debug assertion in dispatch_on_exit or on its termination fold.

Still different from Node in the probe programs:

• The exit code after a throw or after process.emit("error") in an 'exit' listener (above).
• An EventTarget listener's throw in an 'exit' listener (above). Equal to Node on main, different now.
• Promise jobs that an 'exit' listener queues do not run (Run the promise jobs of 'exit' listeners and report their rejections when the event loop runs dry #46758).
• A later 'exit' listener still runs after one throws in three cases: an 'uncaughtException' listener handles the throw (the main thread has this case too), the worker already dies of an uncaught error, or the worker's load failed. Node ends the emit at the first throw. Main does the same as this PR in all three.
• A throw from an 'exit' listener after the entry called process.exit(3) exits 1. Node emits 'exit' a second time there and exits 3.
• A terminate() before the worker starts reports 0 or 1 from run to run on both builds. Node reports 0.
• A stop that lands in a listener of an event that script emits with process.emit() is lost when that emit returns. The script that called process.emit() continues, and a later terminate() does nothing. EventEmitter::innerInvokeEventListeners calls each listener through a JSC call() overload that clears the pending exception, the termination included (src/jsc/bindings/webcore/EventEmitter.cpp:271). Main does the same on every route, for example from a timer, so an 'exit' listener that emits another event still has this case.

Other open PRs. #42032 adds the exit-code rule above. #45575 sets exit code 1 in the worker's fatal hook before the listeners run. #46758 runs the promise jobs of 'exit' listeners, and its worker half needs the VM to stay published during the listeners, which this PR provides. Each of the three conflicts textually with this branch in VirtualMachine.rs or web_worker.rs.

Report. No issue reports this. Runs against Node v26.3.0 found it. process.on("beforeExit", () => process.exit()) in the worker avoids the hang on released versions.

Measurements (release builds with symbols, main 179664e against this PR, same toolchain, unless marked debug).

• Calls per VM end (gdb hit counts, 10 empty workers): Process__dispatchOnExit 1 and 1, Bun__GlobalObject__clearExceptionsForExit 1 and 1 (debug build, LTO inlines it).
• Instructions from WebWorker::shutdown entry to VirtualMachine::teardown entry (gdb stepi, code of the exit-sequence functions only): 118 to 144 for a drained worker, lock-prefixed 5 to 6. 119 to 148 for a worker terminated while idle, lock-prefixed 6 to 8.
• Main-thread exit, on_exit entry to return, empty script: 200 to 214 instructions, lock-prefixed 2 and 2.
• .text 82,164,617 to 82,165,129 bytes. .rodata, .data and .eh_frame do not change. One copy of exit_and_free.
• Allocator calls in the same span: 3 and 3 (drained), 0 and 0 (terminated). Syscall instructions: 0 and 0. qemu-x86_64 -strace per-worker totals vary more between runs than any delta, so they show nothing.
• Equal to Node v26.3.0 in 9 of the 16 probe programs with a stable result (main: 6). The 17th is the early terminate() above. Programs that hang: 0 (main: 2).
• Exit flush, 15 drain-route probes (debug): 14 send the same bytes as main. node:http2 over a JS Duplex goes from 1009 to 0 bytes.
• Exception-check validation (debug, BUN_JSC_validateExceptionChecks=1): 0 reports in 15 runs.
• Stress: terminate() timed to land before, inside and after the 'exit' listeners, with listeners that spin, throw, call process.exit() or start a worker. More than 10,000 workers on the release build and about 400 on the ASAN debug build: no crash, no hang, no sanitizer report, and every exit code is one the rules allow.

Suites run on the debug build. worker_threads.test.ts (177 pass), test/cli/lint/js-plugins.test.ts (148 pass), process.test.js (196 pass, 1 fail: the Node version on this host), 56 vendored test-worker-* / test-process-exit* / event and abort tests, the source lints, repl.test.ts, test/js/web/abort/, event-emitter.test.ts. In test/js/web/workers/, four tests miss their 5 s budget on this machine's debug build with and without the change (they read the 1.2 GB debug executable or run LeakSanitizer at exit): "terminate() while fs.readFile completions keep arriving", "the worker runs and its thread exits without leaking", the funnels fs row in the concurrent run, and the late-completion fs.readFile row. The 16 rows and the lint test also pass with the environment of the sanitizer lanes (detect_leaks=1, BUN_DESTRUCT_VM_ON_EXIT=1, exception-check validation).

First version. This PR first changed only WebWorker::exit() to take the caller's VM, which fixed process.exit() in the listener and nothing else. A design review and a self-review replaced it with the order above.

---

no test proof · iteration 0 · platform-specific test(s) that do not run on this machine, deferring to CI, which covers all platforms: test/cli/lint/js-plugins.test.ts

[robobun]

Status: reworked. The head now fixes the three symptoms of one cause.

How it was reproduced, on main 179664e and bun 1.4.3 against Node v26.3.0: a node:worker_threads worker whose event loop runs dry, with a process 'exit' listener that does one of these.

• It is still running when the parent calls worker.terminate(). Main: the listener runs to its end and the worker exits 0. Node and this PR: the listener stops and the worker exits 1.
• It calls process.exit(5). Main: the next statement and the next listener run. Node and this PR: they do not run.
• It throws. Main: the parent never sees the error. Node and this PR: the parent gets 'error'. The worker then exits 1 with this PR, and Node keeps the exit code.

The three programs are in the PR description under Notes. The tests are 16 rows in test/js/node/worker_threads/worker_threads.test.ts (15 fail on main) and one test in test/cli/lint/js-plugins.test.ts.

[coderabbitai]

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Files selected for processing: 8

• src/jsc/VirtualMachine.rs
• src/jsc/bindings/BunProcess.cpp
• src/jsc/bindings/napi.h
• src/jsc/web_worker.rs
• src/runtime/napi/napi_body.rs
• test/cli/lint/js-plugins.test.ts
• test/js/node/worker_threads/worker-exit-listeners-fixture.js
• test/js/node/worker_threads/worker_threads.test.ts

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Walkthrough

Worker shutdown now separates exit-listener execution from final cleanup. The worker delegates VM exit and freeing to VirtualMachine::exit_and_free, which coordinates termination and unpublication. New subprocess tests cover worker exit listeners and plugin exit-handler exceptions.

Changes

Worker exit lifecycle

Layer / File(s)	Summary
Worker publication and shutdown handoff src/jsc/web_worker.rs	WebWorker::shutdown delegates VM exit and freeing to VirtualMachine::exit_and_free. New helpers check and clear VM publication. Failed entry-point loading installs the quiet unhandled-rejection capture handler.
VM exit-handler and teardown phases src/jsc/VirtualMachine.rs, src/jsc/bindings/BunProcess.cpp, src/jsc/bindings/napi.h, src/runtime/napi/napi_body.rs	Exit handling is split into run_exit_handlers and finish_exit. exit_and_free coordinates termination and worker unpublication. Exit listeners run through the generic host-call wrapper. Related comments identify the updated phases.
Exit-listener regression coverage test/js/node/worker_threads/worker-exit-listeners-fixture.js, test/js/node/worker_threads/worker_threads.test.ts, test/cli/lint/js-plugins.test.ts	Subprocess tests cover worker exit-listener scenarios and check output, stderr, and exit status. A lint test covers throwing plugin exit handlers with VM destruction enabled and disabled.

Suggested reviewers: jarred-sumner, alii

Priority: Normal

Merge Risk: Minimal · up to 8f3f8

The worker exit changes have no identified merge-blocking issue. The subprocess test reports stdout alongside exit status, and the inspected exit paths preserve error reporting and exit codes.

Pre-merge checks: 4

Check name	Status	Explanation
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.
Title check		The title clearly and concisely describes the primary change: running worker 'exit' listeners before the VM is unpublished.
Description check		The description is complete and relevant. It explains the problem, cause, fix, behavior changes, trade-offs, and verification results. It does not use the template headings exactly, but the required i…

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Actionable comments posted: 2

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In `@test/js/node/worker_threads/worker_threads.test.ts`:
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[claude]

LGTM — small, well-reasoned fix that makes WebWorker::exit() request termination unconditionally by taking the caller's VM instead of reading the already-nulled self.vm.

What was reviewed:

• Confirmed node_process.rs is the only caller of WebWorker::exit(); the passed vm is the same thread-local VM that self.vm pointed at when non-null.
• Checked VmHandle::request_termination() is idempotent (stop() CAS is a no-op when already Stopping; enter() still succeeds so the trap fires) and the post-listener state matches what the non-reentrant path already reaches shutdown() in.
• Test spawns a subprocess, drains pipes concurrently, and covers both the bug route (loop-drain) and the unchanged process.exit() route as a regression guard.

Extended reasoning...

Overview

The PR fixes a Node compat divergence: process.exit() called from a worker's process.on('exit') listener returned to the listener instead of stopping it. Root cause: WebWorker::exit() only called request_termination() when self.vm was non-null, but shutdown() nulls that pointer before running the 'exit' listeners via vm.on_exit(). The fix changes exit() to take the caller's &VirtualMachine (which Bun__Process__exit already has via global_object.bun_vm()) and call vm.handle_ref().request_termination() unconditionally. Four files touched: the signature change in web_worker.rs, the sole call site in node_process.rs (which also drops a now-resolved @190n TODO), a comment-only update in BunProcess.cpp, and a new two-variant test in worker_threads.test.ts.

Security risks

None. This is thread-lifecycle / termination-ordering code, not attacker-reachable input handling. No new unsafe blocks; the change actually removes an unsafe raw-pointer deref in favour of a safe &VirtualMachine parameter.

Level of scrutiny

Worker termination touches JSC traps and teardown ordering, so I traced the mechanism end to end rather than trusting the diff in isolation. Verified: (1) node_process.rs:71 is the only caller of WebWorker::exit, so the signature change is complete; (2) when self.vm was non-null the old and new code call the same handle_ref().request_termination() on the same VM, so the non-reentrant path is unchanged; (3) VmHandle::request_termination() is idempotent — stop() is a CAS Open→Stopping (no-op if already there) and enter() returns Some while state ≠ Closed, so re-arming the trap is safe; (4) the state on_exit() continues in after the listener unwinds (gate Stopping, trap consumed at the outermost VMEntryScope exit, no pending exception) is exactly what the non-reentrant process.exit() path already produces before reaching shutdown(), so teardown() sees nothing new. The PR description independently documents each of these and reports verification under BUN_JSC_validateExceptionChecks=1.

Other factors

The test follows harness conventions (test.concurrent.each, bunExe()/bunEnv, concurrent pipe drain via Promise.all, single {stdout, stderr, exitCode} assertion) and covers both the bug route (process.exitCode = 3 → loop drain → shutdown() runs listeners with self.vm null) and the already-working route (process.exit(3) at top level, where self.vm is still live) as a regression guard. The PR body cross-checks output against Node v26 and reports the full worker_threads.test.ts and related suites pass. No CODEOWNERS cover these files. The bug-hunting system found nothing.

[robobun]

^{Updated 1:12 PM PT - Oct 25th, 2026}

✅ @robobun, your commit 8f3f8388fe3d971bbf2c864fd022cd1f1815a7b2 passed in Build #132719! 🎉

---

🧪   To try this PR locally:

bunx bun-pr 40132

That installs a local version of the PR into your bun-40132 executable, so you can run:

bun-40132 --bun

[claude]

I reviewed this PR and didn't find any bugs. The fix is well-reasoned and thoroughly tested, but since it touches worker-thread termination and the process exit path (both critical lifecycle code), a human look would still be worthwhile.

What was reviewed:

• WebWorker::exit() has exactly one caller (Bun__Process__exit), updated in the same PR; VmHandle::request_termination() is idempotent, so the removed null-guard is safe.
• The dispatch_on_exit wrapper matches the established from_js_host_call_generic + report_error_or_terminate pattern already used in flush_logs and dispatch_on_before_exit; the emit loop clears per-listener exceptions, so this is defensive on the main-thread path.
• The test covers both routes to the 'exit' listeners (loop drain — the bug — and outer process.exit()), drains pipes concurrently, and uses the file's combined-object assertion pattern.

Extended reasoning...

Overview

The PR fixes a Node compat bug where process.exit() inside a worker's process.on('exit') listener returned instead of stopping. Root cause: WebWorker::exit() gated the termination request on self.vm being non-null, but shutdown() nulls that pointer before running the 'exit' handlers. The fix passes the caller's &VirtualMachine (which is always live at the call site) and requests termination unconditionally. A secondary defensive change wraps Process__dispatchOnExit in from_js_host_call_generic so a termination that escapes the emit loop lands cleanly in on_exit() rather than riding through subsequent teardown.

Files touched: src/jsc/web_worker.rs (signature change + comment), src/runtime/node/node_process.rs (single call site update, dead TODO removed), src/jsc/VirtualMachine.rs (dispatch wrapper), src/jsc/bindings/BunProcess.cpp (comment correction — the old parenthetical is no longer true), and a new test.concurrent.each block in worker_threads.test.ts.

Security risks

None. No user-controlled input, no auth/crypto/permissions, no new resource acquisition. The change tightens the termination contract; it does not open any new surface.

Level of scrutiny

High. Worker-thread termination and the process exit sequence are critical, subtle lifecycle paths where re-entrancy, exception scopes, and cross-thread state interact. The core fix (pass vm instead of reading self.vm) is straightforward once the problem is understood, and request_termination() is idempotent. The dispatch_on_exit wrapper also runs on the main thread; I verified that (a) the emit loop already clears per-listener exceptions so the new fold is defensive there, (b) report_error_or_terminate short-circuits via is_shutting_down() in the worker case, and (c) the PR body reports main-thread throwing-'exit'-listener behavior is unchanged. Still, this is exactly the kind of path where a maintainer familiar with the JSC termination model should sign off.

Other factors

The PR body demonstrates a deep understanding of the mechanism (VmHandle gate vs. NeedTermination trap, where the TerminationException lands, why the emit loop currently clears it). Verification is thorough: the new test fails on main and passes with the fix; the full worker_threads.test.ts (139 tests), process.test.js, worker.test.ts, worker-terminate-lifetime.test.ts, and 19 vendored Node exit tests were run; BUN_JSC_validateExceptionChecks=1 was checked. All CodeRabbit and comment-cop feedback has been addressed and resolved. No prior review from me on this PR.

[claude]

Nothing blocking. The comments below are optional suggestions. There is no need to push a fix for them before merging.