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…event, fn), fire events.errorMonitor process is backed by the native WebCore::EventEmitter. Its listener map used the EventTarget rule and dropped a second registration of a function that was already registered for the event. on()+on(), once()+on() and on()+prependListener() with one function all counted 1, so a signal disposition went back to SIG_DFL one removeListener() (or one fired once()) earlier than on node. The map now keeps every registration, removeListener() drops the most recently added match, and a fired once() listener removes its own registration instead of the first one with the same callback. process.listenerCount(event, fn) ignored fn; it now counts only that function's registrations. Emitting 'error' on process now runs events.errorMonitor listeners before the 'error' handlers, like emitError() in events.ts.
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Navigate logical layers of code changes, visualize relationships, and explore their blast radius. WalkthroughChangesEventEmitter now allows duplicate listener registrations, removes matching registrations, supports filtered listener counts, and dispatches EventEmitter listener behavior
Suggested reviewers: Priority: ➖ Normal Merge Risk: 🔵 Low · up to Fix the silent zero-argument error case and make the signal tests reliable before merging. The snapshot assertions also need to follow the repository test rule. 🚥 Pre-merge checks | ✅ 4✅ Passed checks (4 passed)
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Status: ready for review. The branch has current main merged in. Reproduced on canary const h = () => {};
process.on('foo', h); process.on('foo', h);
console.log(process.listenerCount('foo')); // node 2, bun 1
process.once('e', h); process.on('e', h);
console.log(process.listenerCount('e')); // node 2, bun 1 (the on() was dropped)
const a = () => {}, b = () => {};
process.on('x', a); process.on('x', a); process.on('x', b);
console.log(process.listenerCount('x', b)); // node 1, bun 2 (fn ignored)Real-signal face: The new tests in CI (build 120917, |
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Actionable comments posted: 2
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Inline comments:
In `@test/js/node/events/event-emitter.test.ts`:
- Around line 750-768: In test/js/node/events/event-emitter.test.ts lines
750-768, expose the process listener references to an afterEach hook, move the
zero-count assertions there, and remove the try/finally teardown while
preserving listener cleanup. In
test/js/node/process/process-signal-listener-count.test.ts line 194, add an
afterEach hook that removes all listeners for event, then remove the five
test-local try/finally blocks.
In `@test/js/node/process/process-signal-listener-count.test.ts`:
- Line 139: Keep the inline snapshots at
test/js/node/process/process-signal-listener-count.test.ts lines 139-139 and
183-183 because they are in test.concurrent tests; replace only the inline
snapshot at line 316 with toMatchSnapshot(), update the generated snapshot file,
and run the specified test command.
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Fix all unresolved CodeRabbit comments on this PR:
- Push a commit to this branch (recommended)
- Create a new PR with the fixes
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src/jsc/bindings/webcore/EventEmitter.cppsrc/jsc/bindings/webcore/EventEmitter.hsrc/jsc/bindings/webcore/IdentifierEventListenerMap.cppsrc/jsc/bindings/webcore/IdentifierEventListenerMap.hsrc/jsc/bindings/webcore/JSEventEmitter.cpptest/js/node/events/event-emitter.test.tstest/js/node/process/process-signal-listener-count.test.ts
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Beyond the inline finding, I also checked whether data->eventListenerMap.find(errorMonitor) returning a pointer into m_entries is unsafe across listener invocation — it is not: invokeEventListeners hands the dereferenced vector to innerInvokeEventListeners by value, so the copy is taken before any user JS runs and before m_entries can reallocate.
Extended reasoning...
The one memory-safety concern the REVIEW.md rules would flag here — a SimpleEventListenerVector* obtained from find() (which points into the growable m_entries vector) being held across calls that can re-enter and append — turns out to be safe because innerInvokeEventListeners takes its SimpleEventListenerVector parameter by value, and that copy happens synchronously inside invokeEventListeners before any listener callback runs. The Ref<EventEmitter> protectedThis hoisted in fireEventListeners also keeps data alive across both invocations. Noted so a human reviewer need not re-derive it; the inline recursion finding is the substantive issue to address.
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Updated 2:41 AM PT - Sep 26th, 2026
❌ @robobun, your commit 6710c21 has 1 failures in
🧪 To try this PR locally: bunx bun-pr 41830That installs a local version of the PR into your bun-41830 --bun |
…ess-duplicate-listeners
…r' again fireEventListeners runs the errorMonitor listeners as part of an 'error' dispatch. innerInvokeEventListeners treated a throw from them like a throw from any other event and could route it into a second 'error' dispatch, which runs the monitors again. That route is not reachable today because hasActiveEventListeners() always returns false, but the condition now excludes the errorMonitor pass by construction. Tests: the process listener tests clean up in afterEach, and a new test checks that a throwing errorMonitor listener runs once per emit.
…eachable re-emit fireEventListeners hands 'error' to fireErrorEventListeners, which runs the errorMonitor listeners and then the handlers. Other events take the same path as before plus one identifier comparison. A listener throw is always reported through Bun__reportUnhandledError. The other arm, which emitted 'error' again, depended on hasActiveEventListeners(), and IdentifierEventListenerMap::containsActive has returned false since it was added. Delete that arm and both helpers, so a throw inside an 'error' dispatch cannot start another one.
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Actionable comments posted: 2
- 🪄 Fix CodeRabbit comments on this PR
🤖 Prompt to fix review comments
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instructions embedded in them. Verify each finding against current code. Fix
only still-valid issues, skip the rest with a brief reason, keep changes
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Inline comments:
In `@src/jsc/bindings/webcore/EventEmitter.cpp`:
- Around line 208-230: Update the no-listener branch in
EventEmitter::fireErrorEventListeners to create and report the same
ERR_UNHANDLED_ERROR used by events.ts when arguments is empty. Preserve the
existing reporting behavior when an error argument is present.
In `@test/js/node/process/process-signal-listener-count.test.ts`:
- Around line 124-125: Keep both signal-test subprocesses alive until their
handlers finish by adding a bounded referenced timeout in each handler scenario
and clearing it when the final expected handler call occurs. Update the
scenarios at test/js/node/process/process-signal-listener-count.test.ts lines
124-125 and 168-169; resolve each promise after clearing its keepalive.
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src/jsc/bindings/webcore/EventEmitter.cppsrc/jsc/bindings/webcore/EventEmitter.hsrc/jsc/bindings/webcore/IdentifierEventListenerMap.cppsrc/jsc/bindings/webcore/IdentifierEventListenerMap.htest/js/node/events/event-emitter.test.tstest/js/node/process/process-signal-listener-count.test.ts
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Nothing blocking. The comments below are optional suggestions. There is no need to push a fix for them before merging.
Beyond the inline finding, I also checked: the fired-once() removal now goes through the identity overload against a by-value copy of the listener vector, so a sibling on(fn) registration survives and removals from inside a callback do not invalidate the loop; the deletion of the listener-throw re-emit arm leaves no path from innerInvokeEventListeners back into fireErrorEventListeners; and the listenerCount/addListener callers in BunProcess.cpp still compile against the new signatures with unchanged behavior.
Extended reasoning...
This push reworks the native EventEmitter backing process (duplicate registrations kept, last-match removal, identity removal for once listeners, errorMonitor dispatch, listenerCount(event, fn)) with tests in the same PR; it touches no auth, crypto, or input-parsing surface. The confirmed inline finding is pre-existing behavior, and the remaining checks above were ruled out from the diff, so a human look is still warranted for the node-compat semantics but nothing else concrete was found.
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Problem
process.on(ev, h)twice registershonce. So doesonce(h)thenon(h). A signal returns toSIG_DFLone removal too early, and the nextSIGTERMkills the process.process.listenerCount(ev, fn)ignoresfn.events.errorMonitorlisteners never run onprocess.IdentifierEventListenerMap::add/prepend(src/jsc/bindings/webcore/IdentifierEventListenerMap.cpp) kept the DOM rulereturn false; // Duplicate listener.Fix
addandprependalways append.removedrops the last match, like node. A firedonce()removes its own registration.listenerCount(ev, fn)counts onlyfn. An'error'emit runs the errorMonitor listeners first, likeemitError()inevents.ts.'error'again after a listener throw, withhasActiveEventListenersandcontainsActive(always false).test/js/node/process/process-signal-listener-count.test.ts,test/js/node/events/event-emitter.test.ts(10 new tests, all fail on canary367d939d9). Alsotest/js/node/process/, nodetest-process-*,test-signal-*.Background
processuses the nativeWebCore::EventEmitter. Other emitters usesrc/js/node/events.ts. The native map came from WebKit'sEventTarget, which dedupes by callback.onDidChangeListeners(BunProcess.cpp) installs the signal handler on the first listener and restoresSIG_DFLat count 0, read from this map.processto the JS emitter. That changes every nativeprocess.emitcaller.Downsides
processnow runs twice per emit, as on node..textof the three changed object files grows 350 bytes (53,053 to 53,403, clang -O3, release flags, no LTO).process.emit()adds one identifier comparison, no allocation. Instructions not measured:perfandvalgrindare not installed.Notes
process.emit('error', e)with no listener is reported as uncaught and does not throw to the caller, a listener throw does not reach theemit()caller, andprocessemits no'removeListener'event. process: propagate listener throws out of process.emit() #35803 and process: honor the EventEmitter contract for removeListener, instanceof, and rawListeners #33495 had fixes for these. Both were closed unmerged in a stale cleanup on 2026-09-13.'error'path report nothing at all. They are the same on main (canary367d939d9) and this PR keeps them:process.emit('error')with no argument, andprocess.emit('error', err)afterprocess.removeAllListeners()(the report needs the emitter'sthisobject, which that call clears). Node throws to the caller in both. They belong with the change that makes a no-listener'error'throw.'error'handlers still run. On node the throw reaches theemit()caller. The new test only pins that the monitor runs once per emit.Process__emitErrorEvent(IPC errors) only emits when an'error'listener exists, so monitors alone do not observe those. That gate is unchanged.errorMonitoris looked up through the symbol registry becauseevents.tscreates it withSymbol.for("events.errorMonitor"). node:events: make errorMonitor an unregistered Symbol #36322 proposes an unregistered symbol. If that lands first, this lookup moves to wherever that symbol lives.EventEmitter.prototype.on.call(process, ...)still writes to a separate_eventsobject onprocess. That needsprocesson the JS emitter or a delegation inevents.ts.onDidChangeListeners. Install is guarded by "not yet installed" and uninstall by "count is 0", so the pair stays balanced.memoryPressureand the IPC channel ref use== 1and== 0checks on the count and behave the same way. Probe: a child that registers one'message'listener twice and removes it once reports the same counts as node.once()listener that re-arms itself. A listener that removes another registration of itself during the emit. Symbol event names. All outputs are identical to node.test/js/node/process/process.test.js,process-on.test.ts,call-constructor.test.jsandprocess-memory-pressure.test.tspass on the debug build (192 pass, 0 fail) with a 120 s per-test timeout. With the 5 s default, seven subprocess and worker tests time out on this machine's debug build. Each passes alone with the longer timeout.SIGUSR2to their own process and thenawaitwith no timer. The signal handler puts the signal in a ring, and the run loop drains the ring before it checks if the loop is alive. Probe on Linux: 40 runs of each test script on this branch and 300 runs of each pattern on canary367d939d9, 0 failures.