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WebWorker::spin calls script with no script frame beneath it in two places after the entry point settles: the entryEvaluated hook, and the report of an entry point that rejected. A process.exit() or a parent terminate() inside one of them returns to spin with a TerminationException pending. spin went on to its start-up GC, and debug and ASAN builds aborted there at vm.hasTerminationRequest(). spin now checks has_requested_terminate() after each of the two calls and goes to shutdown(), as it already does before the entry point loads and after each loop turn.
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Included review availability: This review used your included allowance. Your plan provides up to 10 included reviews per hour; 0 remain after this review. WalkthroughWorker startup now stops when entry-settling handlers request termination and flushes logs before shutdown. Entry rejection continues only when handled and termination was not requested. Subprocess tests cover handler-triggered termination, heap-snapshot rejection, and suppression of queued ChangesWorker startup termination
Suggested reviewers: Priority: ➖ Normal Merge Risk: ⚪ Minimal · up to Workers now stop startup when a handler requests termination, rather than continuing into startup work. The covered cases show no remaining merge-blocking concern; merge after normal checks. 🚥 Pre-merge checks | ✅ 4✅ Passed checks (4 passed)
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Updated 11:19 PM PT - Oct 2nd, 2026
✅ @robobun, your commit fa9690f7ae259879d57a58477c3dff3e454ef259 passed in 🧪 To try this PR locally: bunx bun-pr 44486That installs a local version of the PR into your bun-44486 --bun |
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I reviewed this PR and didn't find any bugs in the two new checks, but since it changes worker shutdown ordering in native lifecycle code (and was not run on macOS/Windows), a human look would still be worthwhile.
What was reviewed:
- Both new
has_requested_terminate()checks inspin(src/jsc/web_worker.rs:888 and :916): tracedprocess.exit()and parentterminate()throughexit()/request_termination()to the flag; the loop-side effect ofobserve_entrynow returningStopis equivalent to the existing post-tick terminate break, and exit code /stopped_by_parenthandling is unchanged. - One same-class site is not covered and the PR does not say it is excluded on purpose:
WebWorker__workerGlobalScopeStarted(line 940) delivers buffered Web Worker'message'events synchronously when the entry installed a listener (WorkerMessagingProxy.cppdeliver(context)), so aprocess.exit()/terminate()landing there still reaches the start-up GC at line 950 with the termination pending. I could not run a debug build here to confirm it aborts, so flagging it for a human to weigh rather than as a finding. - The getHeapSnapshot
ERR_WORKER_NOT_RUNNINGbehavior change matches Node and is pinned by a test row; all rows assertsignalCode: nulland drain pipes concurrently.
Extended reasoning...
The diff adds two termination checks to WebWorker::spin in src/jsc/web_worker.rs so a worker stopped from the entryEvaluated hook or an uncaughtException handler goes straight to shutdown() instead of running the start-up GC with a TerminationException pending, plus seven subprocess tests in test/js/node/worker_threads/worker_threads.test.ts. It touches no security-sensitive surface. The code change is small and consistent with the surrounding terminate-check pattern, and the tests follow harness conventions. Deferring rather than approving because it alters worker lifecycle ordering (a worker now never reaches Running in these cases, which changes getHeapSnapshot behavior), the author reports no macOS/Windows verification, and a sibling synchronous-script site (workerGlobalScopeStarted before the GC) remains unguarded without a stated reason.
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Status: ready for review. Reproduction on a debug build of main: // repro.cjs
const { Worker } = require("node:worker_threads");
const worker = new Worker(
'process.setUncaughtExceptionCaptureCallback(() => process.exit(42)); throw new Error("boom");',
{ eval: true },
);
worker.on("exit", code => console.log("exit", code));
The new rows: CI: the diff is green. The one failing job in builds 123036 and 123080 is |
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On the
A third check after line 940 would be a line that no test fails on. For such a worker |
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Actionable comments posted: 1
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Inline comments:
Review comments at @test/js/node/worker_threads/worker_threads.test.ts:
- Line 799: Replace the timed wait in the worker-thread test with an event-loop
turn by changing setTimeout to setImmediate and removing the delay argument.
Keep the nextTick callbacks and their behavior unchanged.
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| ], | ||
| // The abort needs an Error whose stack nothing has read yet: the GC formats it. | ||
| [ | ||
| "process.exit() in a 'workerMessage' listener, message buffered while the entry point loaded", | ||
| `globalThis.unreadStack = new Error("kept"); process.on("workerMessage", () => process.exit(7)); setInterval(() => {}, 1000);`, | ||
| `postMessageToThread(worker.threadId, "hello").catch(() => {});`, | ||
| ["exit 7"], | ||
| ], | ||
| [ | ||
| "terminate() landing in a 'workerMessage' listener, message buffered while the entry point loaded", | ||
| `globalThis.unreadStack = new Error("kept"); process.on("workerMessage", () => { ${spinUntilTerminated} }); setInterval(() => {}, 1000);`, | ||
| `postMessageToThread(worker.threadId, "hello").catch(() => {}); ${terminateOnMessage}`, |
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🟡 nit (optional): on a release build, deleting the new check at src/jsc/web_worker.rs:888 breaks no test, so a release-only CI lane cannot catch its regression. The two 'workerMessage' rows here print "exit 7" / "exit 1" with or without that check; only debug and ASAN builds abort, and the single row that differs on release (getHeapSnapshot) exercises the observe_entry clause, not this one. Fix: make each load-bearing clause fail a test on every build, e.g. add a 'workerMessage' row whose parent also holds a pending worker.getHeapSnapshot() and expects "snapshot rejected ERR_WORKER_NOT_RUNNING", since without the check the worker still reaches Running and the snapshot resolves.
Why this was flagged
Without the check at src/jsc/web_worker.rs:888 on a release build, the 'workerMessage' process.exit(7) row runs: WebWorker__entrySettled runs the listener, process.exit(7) sets exit_code and requests termination, observe_entry at web_worker.rs:923 sees a fulfilled entry promise and returns Continue, WebWorker__workerGlobalScopeStarted at web_worker.rs:939 moves the proxy to Running, run_gc at web_worker.rs:949 does not assert on release, the loop breaks at web_worker.rs:959 and shutdown reports exit 7. The row's expected lines are identical, so the test passes both ways on release; the getHeapSnapshot row only covers the observe_entry change at web_worker.rs:916. REVIEW.md asks that deleting each load-bearing clause of the fix break at least one test. A pending getHeapSnapshot() in the 'workerMessage' rows would distinguish: with the check the proxy never reaches Running and rejectAllCrossVMRequests (WorkerMessagingProxy.cpp:564) rejects it; without it the pending task runs after workerGlobalScopeStarted and resolves.
Verification: Without the new check at src/jsc/web_worker.rs:888-891, the two 'workerMessage' rows take observe_entry line 902 -> Continue, run_gc line 949 (the ASSERT in VMTraps.cpp is compiled out in release), then the loop at 957-961 breaks and shutdown() runs with exit_code already 7. Stdout is "exit 7"/"exit 1", exactly what the test at test/js/node/worker_threads/worker_threads.test.ts:775 expects.
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Problem
ASSERTION FAILED: vm.hasTerminationRequest()(VMTraps.cpp(540),deferTerminationSlow) whenprocess.exit()or a parentterminate()stops a worker inside anuncaughtExceptioncapture callback for an entry point that throws, or inside a'workerMessage'listener that the start sequence runs.WebWorker::spin(src/jsc/web_worker.rs) calls both with no script frame beneath, so the TerminationException is still pending whenspinruns its start-up GC. Since Preserve a pending exception across the GC stack-trace finalizer #33584 that GC asserts.Fix
spincheckshas_requested_terminate()after each of the two calls and goes toshutdown(), as it does after each loop turn.Running. AgetHeapSnapshot()that waits for it rejects withERR_WORKER_NOT_RUNNING, as in Node.test/js/node/worker_threads/worker_threads.test.ts. Withsrc/at main, 6 rows fail on a debug build (SIGABRT) and 1 on a release build. Also the other worker test files and 111 vendored Node worker tests.Background
shutdown()does.entryEvaluatedhook (it delivers bufferedpostMessageToThreadmessages), the report of a rejected entry point, a GC, then the first loop turn.VirtualMachine::uncaught_exception. A pending termination is what stopsJSNextTickQueue::drain, so a queued tick then ran afterprocess.exit().Downsides
getHeapSnapshot()above resolved before..textstays 58,185,397 bytes.Notes
Reach. Assertions are on in debug and ASAN builds only. A release build prints the same lines with and without the fix in every row except the
getHeapSnapshot()row. No released version has the abort: the asserting scope (DeferTerminationForAWhileincomputeErrorInfoWrapperToString,src/jsc/bindings/FormatStackTraceForJS.cpp) came with #33584 (d27fef0), after bun-v1.4.2. The abort also needs anErrorwhose stack nothing has read yet, because that is what the GC formats. The thrown entry error is one. The'workerMessage'rows keep one in a global.Measured on linux x64. The fix runs are on main 519963e. The runs with
src/at main are on bc7a813.process.exit(42), CommonJS entry throwsexit 42exit 42exit 42exit 42exit 42exit 42'workerMessage'listener callsprocess.exit(7)exit 7exit 7exit 7terminate()lands in the capture callbackexit 1exit 1exit 1terminate()lands in the'workerMessage'listenerexit 1exit 1getHeapSnapshot()pending, capture callback exitsERR_WORKER_NOT_RUNNING,exit 42exit 42ERR_WORKER_NOT_RUNNING,exit 42terminate()src/at main 152 pass, 6 fail. With the fix 158 pass, 0 fail.observe_entry, the 2'workerMessage'rows fail.terminate()rows are why the predicate ishas_requested_terminate()and notexit_called.WebWorker__workerGlobalScopeStartedalso runs script with no frame beneath it: amessagelistener, for a message that arrived during load. It needs no check.drainInboxruns the microtask checkpoint after each message, andZig::GlobalObject::drainMicrotaskstakes the termination there (seen in a debugger). 5 programs withprocess.exit()orterminate()in that listener, 3 runs each on a debug build: no abort.process.exit()) passes on main. It pins the behavior that the rejected shape broke: no existing test failed on it.'uncaughtException'listener that callsprocess.exit()for an entry point that throws takes the same path. It did not abort before. A pendinggetHeapSnapshot()now rejects there too, as in Node.BUN_JSC_validateExceptionChecks=1on the new rows: no report (a control file reports, so the validator was active).test/js/web/workers/*, the othertest/js/node/worker_threads/*files andmodule-graph-workers.test.ts. Every failure was a 1 s or 5 s timeout under host load that passes on a rerun or with a longer timeout, except two tests inworker-terminate-lifetime.test.tsthat fail the same way on main. 111 vendoredtest-worker*files pass..text58,185,397 bytes, both unchanged (size -A). Byobjdumpthe worker thread function goes from 916 to 902 instructions. One of the four entry checks moves out of line (291 bytes, 75 instructions) and runs once per worker start. The three checks in the loop stay inline.Self-review. The first shape wrapped the call of
Bun__handleUncaughtExceptionso that the reporter took the termination. The review built it and several alternatives. It found that the take lets aprocess.nextTickcallback queued behind the throwing one run afterprocess.exit(), that it changes an exit code, and that the'workerMessage'case still aborts. Rejected: raising JSC's VM entry guard where bun forbids execution, and generated exception checks for every raw extern. Both support a take inside the reporter, which this PR does not make.Not verified. macOS and Windows were not run.
Separate defects seen, not changed here. Observed on bun 1.4.3-canary.1+367d939d9 (release):
process.on("uncaughtException", () => process.exit(42))lets a tick that was queued behind the throwing tick run. Node runs none.worker.terminate()never resolves. Node ends the worker._fatalExceptiongetter that callsprocess.reallyExit(7)in a worker gives exit code 1. Node gives 7.'workerMessage'listener runs before a throwing entry point's error is reported, so a listener that exits hides the error (exit 7). Node prints the error and exits 1.Open PRs #40128 and #44252 may cover the first two. They were not run against these programs.
Found while working on #44170. This PR does not change that issue.