MessagePort: close a port whose peer closed, so it is rejected as a transferable - #38066
MessagePort: close a port whose peer closed, so it is rejected as a transferable#38066robobun wants to merge 6 commits into
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When one side of a channel is close()d, node closes the other side as well once the close has propagated: from then on the port is rejected as a transferable, postMessage() on it is dropped and its loop refs are released. Bun only fired 'close' on the peer and left it entangled, so a port whose peer had closed could still be transferred, and a port with no listeners was never told at all (a ref()'d one pinned the loop forever). peerClosed() now closes the port through close() once nothing the peer sent is still queued. A port that is not receiving keeps what is queued and stays open until it is drained, like node, where the close notification is an entry behind the data: attach() re-notifies once the port starts, and tryTakeMessage() closes on the receiveMessageOnPort() call that finds the queue empty. The pipe learns the port's context when the MessagePort is created instead of when a 'close' listener is added, so the notification reaches a port without listeners too. A peer that was garbage collected rather than closed still does not close the port (node never closes a channel over a collection); it only releases the loop refs of a port that is started or listening for 'close', and leaves an idle port untouched so a later close(cb) still gets its event.
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Status: reproduced on bun 1.4.0 and main with the repro in the description (node v26.3.0 throws DataCloneError, bun accepts the transfer); the listenerless variant hangs on 1.4.0. Fix and tests are in this PR (current revision 5db54a9): 17 of the 22 new tests fail on the release build, the other 5 pin behaviour kept from main; the full worker_threads suite, the neighbouring MessagePort suites and the 28 upstream port tests pass on the debug+ASAN build. CI for 5db54a9 (build 94691): every lane that ran is green (the remaining entries are unrelated tests that passed on retry); the two darwin 14 aarch64 test jobs expired without an agent picking them up, so that lane has not run yet. |
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WalkthroughMessagePort peer-close handling now registers close contexts at creation, drains queued messages before closure, distinguishes explicit closure from garbage-collected peers, and adds lifecycle coverage for transfers, callbacks, and loop references. ChangesMessagePort lifecycle
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In `@test/js/node/worker_threads/worker_threads.test.ts`:
- Around line 1950-1966: Update the collected-peer test around the existing
port1 close listener to await a close event before asserting transferability.
Use the listener on port1 as proof that MessagePort::peerClosed observed peer
collection, then retain the isRejectedAsDetached(port1) assertion and transfer
flow.
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src/jsc/bindings/webcore/MessagePort.cppsrc/jsc/bindings/webcore/MessagePort.hsrc/jsc/bindings/webcore/MessagePortPipe.cppsrc/jsc/bindings/webcore/MessagePortPipe.htest/js/node/worker_threads/worker_threads.test.ts
…tests A WeakRef on the dropped port has to clear before the assertions run, so the tests fail instead of passing vacuously if the peer is not collected.
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Additional findings (outside current diff — PR may have been updated during review):
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🔴
src/jsc/bindings/webcore/MessagePort.cpp:555-557— RemovingregisterCloseContext()here, combined with the new idle-port no-op inpeerClosed()'s collected-peer branch, leaks: if the peer is GC'd while this port is idle,peerClosed()returns without settingm_closeEventDispatched, and a'close'listener added afterwards makesvirtualHasPendingActivity()(m_hasCloseEventListener && !m_closeEventDispatched) return true forever — nothing re-notifies (attach()only runs from'message'/start(),tryTakeMessage()ignoresCollected, andregisterCloseContext()would early-return onContextKnownanyway). Pre-PR the retroactive call here re-delivered and setm_closeEventDispatched, so this is a leak regression; it is distinct from the :296 finding (that one needs a listener present at collection time plus a buffered message, and its fix does not reach this case). Re-notifying fromaddEventListener('close')when the peer isClosed-but-not-ClosedByRequestrestores the pre-PR release; settingm_closeEventDispatched = truein the idle no-op instead would break the newclose(cb)-after-collected-peer test.Extended reasoning...
What the bug is
This PR makes two changes that together open a permanent-pin path:
MessagePort::create()now callsregisterCloseContext(), soContextKnownis set from birth (MessagePort.cpp:55).addEventListener('close')no longer callsregisterCloseContext()(:555-557).peerClosed()'s collected-peer branch now no-ops on an idle port — "An idle port is left alone: its 'close' belongs to whoever eventually closes it" (:306-310).
If the peer is garbage-collected while this port has no listeners, (1) means the notification is delivered, (3) means it does nothing, and (2) means a
'close'listener added afterwards has no way to re-trigger it.m_hasCloseEventListeneris then true,m_closeEventDispatchedstays false, andvirtualHasPendingActivity()at :449 returns true for the rest of the context's life.Step-by-step proof
let p; (() => { const ch = new MessageChannel(); p = ch.port1; })(); // port2 unreachable Bun.gc(true); // ~MessagePort → pipe->close(1, Collected) → notifyPeerClosed(0) await new Promise(r => setImmediate(r)); // peerClosed() task runs p.on('close', () => {}); // m_hasCloseEventListener = true p = null; // wrapper is now unrooted from JS… Bun.gc(true); // …but virtualHasPendingActivity() keeps it alive forever
port2has no listeners, so itsvirtualHasPendingActivity()is false and the wrapper is collected.~MessagePort()→m_pipe->close(1, CloseKind::Collected)→ side 1 becomesClosed(notClosedByRequest) →notifyPeerClosed(0).- Side 0 has
ContextKnown(set by this PR'screate()), sonotifyPeerClosed()posts the task. - Task runs →
port1.peerClosed(): not detached/closing;m_started == false→ skip flush;queuedCount == 0→ no early return;!isOtherSideClosedByRequest→ collected-peer branch;m_started || m_hasCloseEventListeneris false → return without touchingm_closeEventDispatched. p.on('close', ...)setsm_hasCloseEventListener = true. TheregisterCloseContext()call that used to be here is gone; even if it were still there, it early-returns onContextKnown(MessagePortPipe.cpp:252).virtualHasPendingActivity():m_hasCloseEventListener && !m_closeEventDispatched→ true, permanently.
Why nothing recovers it
attach()re-notifies on aClosedpeer (MessagePortPipe.cpp:241), but is only reached fromstart()/addEventListener('message')— never from a'close'listener.tryTakeMessage()closes only onisOtherSideClosedByRequest()(:411) — false forCollected.registerCloseContext()early-returns onContextKnown, whichcreate()already set.- The retroactive-close-on-listener-add path is exactly what this PR deletes.
The wrapper, its
'close'listener closure and everything that closure captures, and the pipe are pinned until context teardown. (Not a loop-ref hang — a bare'close'listener does not ref the loop — but a per-port memory leak.)Regression
Pre-PR,
create()did not setContextKnown, so at step 2notifyPeerClosed()early-returned on!(st & ContextKnown)and the collection-time notification was dropped. At step 4 the oldaddEventListener('close')calledregisterCloseContext(), which setContextKnown, observed the peerClosed, and re-notified; the oldpeerClosed()then unconditionally calleddispatchCloseEvent()→m_closeEventDispatched = true→ not pinned. The PR description says the retroactive'close'was "deliberately dropped" because "for a collected peer node fires nothing at all" — that is fine for observable behaviour (node never collects an entangled port, so there is nothing to match), but it does not account for thevirtualHasPendingActivity()pin the retroactive dispatch used to release.Distinct from the existing :296 finding
The :296 finding needs the
'close'listener present at collection time plus a buffered message soqueuedCount > 0gates the collected-peer branch. Its proposed fix (guard the queuedCount check withisOtherSideClosedByRequest()) reaches the collected-peer branch, which then seesm_hasCloseEventListener == trueand dispatches — so that fix works for that scenario. HerequeuedCount == 0and the collected-peer branch is reached but no-ops because the listener is not present yet; the :296 fix does not help.Fix
Re-notify from
addEventListener('close')for the collected-peer case only, e.g.:} else if (eventType == eventNames().closeEvent) { m_hasCloseEventListener.store(true, std::memory_order_release); // A collected peer's notification may have reached us while we were idle and no-opped; // now that we're listening, let the collected-peer branch fire and release the GC pin. if (isEntangled() && !m_closeEventDispatched && (m_pipe->state(1 - m_side) & MessagePortPipe::Closed) && !m_pipe->isOtherSideClosedByRequest(m_side)) { queueTaskKeepingObjectAlive(*this, TaskSource::PostedMessageQueue, [](MessagePort& p) { p.peerClosed(); }); } }
This restores the pre-PR release for the bun-specific collected-peer scenario and is consistent with the rule the collected-peer branch already follows ("a port that is … listening for 'close' is still told"). The
!isOtherSideClosedByRequestguard keeps the explicit-close path unchanged (there the port is already closed by the time a late listener is added, soisEntangled()is false anyway).The simpler-looking alternative — set
m_closeEventDispatched = truein the idle no-op — would make a laterclose(cb)'sdispatchCloseEvent()early-return and never callcb, breaking the new"a port whose peer was garbage collected still delivers close(cb) when it is closed later"test.
… close A collected peer is handled the way main handled it: a started or 'close'-listening port is told right away even with messages queued, since nothing would re-notify a 'close'-listening port that never starts, and it stays pinned until 'close' has been dispatched. tryTakeMessage() re-reads this side's queue after seeing the peer's ClosedByRequest, so a message the peer sent between takeOne() and its close() is not dropped by closing the port.
…er, keep transfers on a closed port
Whether a peer's close waits behind the queued messages now follows
node's receiving_messages_ (m_receiving): set by start() or a 'message'
listener, cleared when the last 'message' listener is removed. A port
paused that way keeps the messages for its next listener, as before; a
port that was start()ed and never listened closes right away, since
nothing would ever drain it.
peerClosed()'s flush stops when a handler removes the last listener, as
the drain does, so a once() handler on a received port leaves the rest
of the queue for the next listener instead of dispatching it to nobody.
registerCloseContext() re-reports an already closed peer even when the
side is registered, and addEventListener('close') calls it again, so a
port that ignored a collected peer while it had no listener is told once
it listens for 'close' (and is not kept alive waiting for that event).
postMessage() on a closed port disentangles the ports in its transfer
list before dropping the message, as node does; previously a port in the
list stayed usable and its peer was never told.
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Summary of the review rounds so far, all addressed in f0af4bc and d2851de (threads replied to and resolved):
Each fix has a test that fails on the revision before it; the description lists them and now describes the current state, with the earlier revisions summarized in a details block. |
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d2851de addresses both prior open findings: the start()ed-but-listenerless hang is now gated on m_receiving (with the new "start()ed port without a 'message' listener" test), and the late-'close'-listener leak after a collected peer is fixed by registerCloseContext() re-notifying past ContextKnown (with the new "'close' listener added after the peer was garbage collected" test). One gap remains in the m_receiving mechanism — see the inline comment.
Extended reasoning...
The latest commit introduced m_receiving and restored the registerCloseContext() re-notify in addEventListener('close'), which resolves the two inline findings I left at 07:02 and 07:38 (both still marked unresolved in the thread but verified fixed against the current diff, each with a new test covering the exact repro). The remaining inline finding this run is a residual in the same fix: start() sets m_receiving = true only after the m_started early-return, so an explicit start() following on()/off() leaves the port paused and the !m_receiving && queuedCount > 0 deferral hangs a .ref()'d port. Not approving given the open finding and the scope of the change (MessagePort lifecycle / GC / cross-thread state).
start() only turned receiving on the first time it ran, so start() on a port whose 'message' listeners had been removed left it paused and a peer close on hold for good. Every call now sets m_receiving and re-attaches, which is also what re-adding a 'message' listener relied on, so addEventListener just calls start().
| // Not receiving with messages queued: node's close notification waits behind them. The | ||
| // next 'message' listener (attach()) or the receiveMessageOnPort() that empties the queue | ||
| // (tryTakeMessage()) completes the close. | ||
| if (!m_receiving && MessagePortPipe::queuedCount(m_pipe->state(m_side)) > 0) | ||
| return; |
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🔴 The !m_receiving && queuedCount > 0 deferral models node's receiving_messages_, but node's same removeListener hook that clears it (stopMessagePort) also calls port.unref() — so a not-receiving port never holds a loop ref there. Bun's removeEventListener (:562-568) clears m_receiving but leaves m_hasRef untouched, so port1.ref(); port1.on('message',h); port1.off('message',h); port2.postMessage('m'); port2.close(); (or .once() + two peer messages) defers here forever with refKeepAlive(+1) never balanced — process hangs. Pre-PR peerClosed() unconditionally jsUnref()'d and it exited; node exits because the pause unref'd the port. Fix: mirror node — release the loop ref when the last 'message' listener is removed (or jsUnref() here even when deferring, so the port stays open/transferable but stops pinning the loop).
Extended reasoning...
What the bug is
peerClosed() at MessagePort.cpp:310-311 defers closing when !m_receiving && queuedCount > 0, keeping the port open until a later 'message' listener (via attach()) or receiveMessageOnPort() (via tryTakeMessage()) drains the queue. m_receiving is modeled on node's receiving_messages_, which node's stopMessagePort clears when the last 'message' listener is removed. But node's setupPortReferencing removeListener hook does two things at that point: it calls stopMessagePort and port.unref(). Bun's removeEventListener at :562-568 replicates only the first — it clears m_receiving but leaves m_hasRef (the explicit .ref() keepalive) alone. So a .ref()'d port paused by removing its last listener still holds Bun__eventLoop__refKeepAlive(+1), and if the peer closes with a message left queued, peerClosed() defers here forever without ever reaching close() — the process hangs.
Step-by-step proof
const { port1, port2 } = new (require('worker_threads').MessageChannel)();
port1.ref();
const h = () => {};
port1.on('message', h);
port1.off('message', h);
port2.postMessage('queued');
port2.close();
setTimeout(() => { console.log('hung, hasRef=' + port1.hasRef()); process.exit(1); }, 3000).unref();port1.ref()→jsRef():isEntangled()true,isOtherSideClosedByRequest()false →m_hasRef=true, self-ref(),Bun__eventLoop__refKeepAlive(vm, +1).port1.on('message', h)→addEventListenercallsstart()(setsm_started=true,m_receiving=true,attach());onDidChangeListenerImplbumpsm_messageEventCountto 1 →m_listenerLoopRefActive=true.port1.off('message', h)→removeEventListenerat :559-568: no more'message'listeners →m_hasMessageEventListener=false,m_receiving=false.onDidChangeListenerImpldrops count to 0 →m_listenerLoopRefActive=false.m_hasRefstays true — nothing in this path touches it.port2.postMessage('queued')→send()appends to side 0's inbox (queued=1), setsDrainScheduled, posts a drain task.port2.close()→pipe->close(1, Explicit)setsClosed | ClosedByRequeston side 1,notifyPeerClosed(0)posts a task.- Drain task runs →
drainAndDispatchhits!port->hasMessageEventListener()(MessagePortPipe.cpp:127-131), clearsDrainScheduled, returns without consuming. queued stays 1. peerClosed()task runs →m_started && hasMessageEventListener()is (true && false) → skip flush.isOtherSideClosedByRequest()is true → skip collected-peer branch.!m_receiving && queuedCount > 0is (true && 1>0) → return at :311.close()at :312 (which would have releasedm_hasRef) is never reached.
Result: m_hasRef's Bun__eventLoop__refKeepAlive(+1) is never balanced → process hangs.
The .once() variant is arguably more realistic and hits the identical path: port1.ref(); port1.once('message', ()=>{}); then the peer sends two messages and closes — the once() consumes the first (its self-removal clears m_receiving), the second is left queued, peerClosed() defers forever.
Why nothing recovers it
attach()re-notifies on aClosedpeer, but is only reached fromstart()or a new'message'listener — the user never adds one and never callsstart().tryTakeMessage()requires a userreceiveMessageOnPort()call; there isn't one.registerCloseContext()(from a late'close'listener) would just re-postpeerClosed(), which hits the same deferral.virtualHasPendingActivity()returns false (no listeners,DrainScheduledclear, peer closed, but queued>0 → actually true on the last line, but irrelevant): even if the wrapper were collected,m_hasRef's self-ref()keeps the C++ object alive and~MessagePort()doesn't release the keepalive.
Why this is a regression
- Pre-PR:
peerClosed()unconditionally calledjsUnref(globalObject), which clearedm_hasRefandBun__eventLoop__refKeepAlive(-1)→ process exited. - Node:
setupPortReferencing'sremoveListenerhandler callsport.unref()alongsidestopMessagePort. libuv ref is a single bit, so this undoes the earlier explicit.ref()— the port stays open (deferred close, matching this PR's intent) but its handle is unref'd → process exits. - The
onmessage = fn; onmessage = nullvariant doesn't hit this becausesetJSMessagePort_onmessageSettercallsjsUnref()on the null assignment; only.ref()+.on/.off(or a fired.once) reaches it.
This is the remaining gap in the m_receiving fix from the previous review rounds: the earlier hangs (start()-only, and pause+start()) were fixed by making start() set m_receiving on every call, but a paused port the user never resumes still holds m_hasRef forever. The three "paused by …" tests don't .ref(), and the two "start() on a paused port" tests .ref() but explicitly resume via start(), so no test in the PR covers .ref() + paused + queued message + peer close + never resumed.
How to fix it
Two options that both match node's observable state (port stays open/transferable, but does not pin the loop):
(a) Mirror node — call jsUnref() (or at least release m_hasRef) in removeEventListener when the last 'message' listener goes, alongside clearing m_receiving. This is exactly what makes node's deferral safe: a not-receiving port never holds a loop ref there. addEventListener's start() path would need to reacquire it (or the user calls .ref() again), which is also what node does.
(b) Release the loop refs when deferring — in peerClosed(), jsUnref() even when taking the !m_receiving && queuedCount > 0 early return. The port stays open/transferable (the close is still deferred), but stops pinning the loop.
Either way, add a spawned-process test alongside the existing "a ref()'d port with no listeners…" one: port1.ref(); port1.once('message', ()=>{}); port2.postMessage('a'); port2.postMessage('b'); port2.close(); and assert the process exits.
| auto result = EventTarget::removeEventListener(eventType, listener, options); | ||
| if (!hasEventListeners(eventNames().messageEvent)) | ||
| if (!hasEventListeners(eventNames().messageEvent)) { | ||
| m_hasMessageEventListener = false; | ||
| // Node stops the port when its last 'message' listener goes. | ||
| if (eventType == eventNames().messageEvent) | ||
| m_receiving = false; | ||
| } |
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🟡 m_receiving = false is set whenever !hasEventListeners(messageEvent) after the base call, without checking result — so port.start(); port.removeEventListener('message', neverAddedFn) spuriously flips m_receiving to false even though nothing was removed (node's [kRemoveListener] → stopMessagePort only fires when the listener was actually found). A subsequent port2.postMessage('m'); port2.close() then defers at the !m_receiving && queuedCount > 0 check in peerClosed() and the port stays open/transferable where node closes it. Gate the assignment on result: if (result && eventType == eventNames().messageEvent) m_receiving = false;.
Extended reasoning...
What the bug is
MessagePort::removeEventListener at MessagePort.cpp:561-567 does:
auto result = EventTarget::removeEventListener(eventType, listener, options);
if (!hasEventListeners(eventNames().messageEvent)) {
m_hasMessageEventListener = false;
if (eventType == eventNames().messageEvent)
m_receiving = false; // ← not gated on `result`
}The m_receiving = false assignment models node's stopMessagePort (which clears receiving_messages_), but node only calls that from the [kRemoveListener] hook, and lib/internal/event_target.js's removeEventListener only invokes this[kRemoveListener] inside the matched-handler branch of its linked-list walk — a not-found removal returns without calling it. So in node, port.removeEventListener('message', fnThatWasNeverAdded) leaves receiving_messages_ untouched; here it flips m_receiving to false whenever there happen to be no 'message' listeners left afterwards (which is trivially true if there never were any).
Step-by-step proof
const { port1, port2 } = new MessageChannel();
port1.start(); // m_receiving = true (set in start())
port1.removeEventListener('message', () => {}); // not found: result = false
port2.postMessage('m');
port2.close();port1.start()→m_started = true,m_receiving = true,attach().port1.removeEventListener('message', neverAdded)→EventTarget::removeEventListenerfinds nothing and returns false.!hasEventListeners(messageEvent)is true (there never were any) andeventType == messageEvent→m_receiving = false.port2.postMessage('m'); port2.close()→ drain task runs,drainAndDispatchbails on!port->hasMessageEventListener()without consuming (queuedCount stays 1).peerClosed()runs:m_started && hasMessageEventListener()is (true && false) → skip flush;isOtherSideClosedByRequest()→ true;!m_receiving && queuedCount > 0at :310 is (true && true) → return.close()is never reached.
Node's behavior for the same sequence: receiving_messages_ stays true after step 2 (not-found removal is a no-op on the hook), so the started port drops 'm' into the void and processes the close — port is closed and rejected as a transferable. This is exactly the case the PR's own "a start()ed port without a 'message' listener is closed even with a message queued" test exercises; that test would fail if a bogus .removeEventListener('message', () => {}) were inserted after port1.start().
Why existing code doesn't prevent it
The .off() fallback at src/js/node/worker_threads.ts:183-184 does const wrapper = byListener?.get(listener) ?? listener; this.removeEventListener(event, wrapper), so .off('message', neverAdded) reaches this path with the raw (never-registered) listener. Nothing in removeEventListener distinguishes "the last listener was removed" from "there were never any listeners and this call removed nothing" — both satisfy !hasEventListeners(messageEvent).
Impact
- Without
.ref(): the port stays open and transferable after its peer closed, where node closes and rejects it — a node-compat divergence in the exact semantics this PR is implementing (m_receivingwas added specifically to model node'sreceiving_messages_). - With
.ref(): the deferral never completes and the process hangs — but that hang is the same mechanism as the separate "deferral doesn't releasem_hasRef" issue; once that is addressed the hang here goes away, leaving only the transferable-vs-rejected divergence.
The trigger (calling removeEventListener/.off() with a function that was never added, on a start()ed port that has no 'message' listeners) is unusual — it's a user-side no-op call — so this is filed as a nit rather than a blocker.
How to fix
Gate the m_receiving = false assignment on result, matching node's [kRemoveListener] semantics:
if (result && eventType == eventNames().messageEvent)
m_receiving = false;(Or equivalently, move the whole m_receiving = false line under an if (result) — the m_hasMessageEventListener = false line above it is idempotent and safe to leave un-gated, since it just re-states !hasEventListeners(messageEvent).)
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Problem
MessageChannelisclose()d, the other port can still be put in a transfer list:carrier.postMessage(port, [port]),structuredClone(x, { transfer: [port] }),worker.postMessage(port, [port])andnew Worker(f, { transferList: [port] })all accept it and ship a dead endpoint. Node throwsDataCloneError: MessagePort in transfer list is already detachedonce the peer's close has been processed (by the time the port's own'close'has fired), because in node the peer's close closes this port too.ref()'d one keeps the process alive forever (port1.ref(); port2.close();hangs; node exits).MessagePort::peerClosed()(src/jsc/bindings/webcore/MessagePort.cpp) dispatched'close'and released the loop refs but left the port entangled (m_isDetached/m_isClosingstayed false), which is the state every transfer path checks: the pre-check inMessagePort::postMessage,SerializedScriptValue::create(src/jsc/bindings/webcore/SerializedScriptValue.cpp, shared by all the entry points above) andMessagePort::disentanglePorts. And the pipe only learned which context to notify fromaddEventListener('close')orstart(), so a listenerless port was never notified.Fix
peerClosed()closes the port throughclose()once nothing the peer sent is left to deliver, so it ends up in the same state as an explicitly closed port: rejected by every transfer path,postMessage()on it dropped, loop refs released,'close'dispatched fromclose()'s task (so inside the'close'handler the port is already closed, as in node).once()handler), exactly as the regular drain does, and leaves the rest queued.receiving_messages_(newm_receiving): never started, or the last'message'listener was removed (node stops the port then, sooff(), a firedonce()andonmessage = nullall defer);start()or a new'message'listener turns it back on (everystart()call re-attaches, which also re-reports a peer that closed while the port was paused). A port that wasstart()ed and never given a listener is receiving: node emits its messages into the void and closes, and bun has no drain for it at all, so it closes right away too (otherwise aref()'d one would pin the loop forever). The deferred close is completed by the next'message'listener (MessagePortPipe::attach()already re-notifies once its drain has run) or by thereceiveMessageOnPort()call that finds the queue empty (tryTakeMessage()closes on it, which is node's behaviour for that call).tryTakeMessage()reads the peer's state before re-reading its own queue, the orderingvirtualHasPendingActivity()already documents, so a message a worker sent right before closing cannot be dropped.MessagePort::create()registers the port's context with the pipe, so the notification reaches a port whether or not it ever gets a listener.registerCloseContext()also re-reports a peer that is already closed, andaddEventListener('close')still calls it (see the next bullet).DataCloneError, the linejsRef()and the existing "hasRef() survives collection of the unreferenced peer" test already draw. As on main, such a port fires'close'and releases its loop refs if it is started or listening for'close'(a listening peer must not pin the process), with no queue deferral. Since the notification now also reaches idle ports, those are left untouched (firing their one'close'early would swallow a laterclose(cb); node's test-worker-message-port.js caught that) and are told once they add a'close'listener, as on main, so they are not kept alive waiting for an event that would never come.postMessage()on a closed port still disentangles the ports in its transfer list before dropping the message, as node does and as main did for a peer-closed port (which was still open); otherwise closing the port here would have left such a port usable and its peer uninformed. This also covers a port closed by its ownclose().'close'listener added after an explicitly closed peer's notification was processed no longer fires (the port is closed by then; node fires nothing either), and a port paused by removing its listener now closes, and is rejected, once a later listener has drained it (main left it open forever).describe("a port whose peer closed is closed too")in test/js/node/worker_threads/worker_threads.test.ts, 22 tests: the report (with the transfer staying atomic andstructuredClone), a receiving port, rejection inside the port's own'close'handler, no listeners at all, a late'close'listener,postMessage()on the closed port consuming its transfer list,Worker.postMessage()and theWorkerconstructor, the deferred cases (never started with a late listener orreceiveMessageOnPort(), the three paused variants,start()without a listener,start()on a paused port before and after the peer's close, transferring the port left open, aonce()handler on a received port), the collected-peer cases (transferable, unread message,close(cb)later, late'close'listener) and theref()hang as a spawned process. 17 fail on the release build; the four collected-peer tests and thepostMessage()one pass there and exist to pin the behaviour kept from main (each failed on the intermediate revision whose mistake it guards against).test-messagechannel/test-worker-message-*/test-worker-workerdata-messageport/test-worker-messagingfiles pass on the debug+ASAN build.hasRef()flips relative to'close'; it reorders the tail ofpeerClosed(), which now goes throughclose()for an explicit peer close, so they compose after a textual rebase), structured clone: re-check the transfer list after serializing so a failed transfer detaches nothing #37966 (re-checking the transfer list after serializing; sameisDetached() || isClosing()predicate this PR makes true for a peer-closed port), worker_threads: MessagePort.postMessage() returns true like Node.js #34011 (postMessage()return value), MessagePort: drain a started port even with no 'message' listener #34912 (draining a started port without listeners; with it, thestart()-only case drains instead of being dropped at close, same outcome), MessagePort: don't close a listening peer when its sibling is GC'd #32564 / MessagePort: pin the entangled peer while a side holds a loop ref #36434 (what a collected peer should do; this PR keeps main's behaviour there).Background
MessageChannelin bun is oneMessagePortPipewith two sides; each JSMessagePortowns one side. Closing a side marks itClosedin the pipe and posts a task to the other side's context, which callspeerClosed()on the port owning that side. The pipe can only post that task if it knows the side's context (registerCloseContext()/attach()).CloseKind::Explicit(close(), context teardown, a transferred port that was never received) additionally setsClosedByRequest;CloseKind::Collected(the owning wrapper was garbage collected while entangled) does not.isOtherSideClosedByRequest()tells them apart.'message'listener, andreceiveMessageOnPort()pops one synchronously.start()is the Web API that turns delivery on; adding a'message'listener calls it implicitly.close()marks the port detached synchronously and dispatches'close'from a queued task, so listeners added right after (andclose(cb)) still see it; the event is dispatched at most once per port.virtualHasPendingActivity()keeps a port's wrapper alive while it is listening for'close'and that event has not been dispatched; this is why an idle port that will never get a peer-side'close'has to be notified once it starts listening.SerializedScriptValue::create, which rejects a port withisDetached() || isClosing()set; closing the port is what makes all of them reject it.node v26.3.0 vs this branch vs bun 1.4.0: a port whose peer posts "x" and then closes
Each line: the port's state a few turns after the peer closed, what a listener added afterwards receives, and the final state (
REJECTED= rejected as a transferable).node v26.3.0 and this branch print the same thing:
bun 1.4.0:
Repro from the report
node v26.3.0 and this branch:
bun 1.4.0:
Listenerless variant (hangs on 1.4.0; exits with
hasRef=falseon node and this branch):Earlier revisions of this PR
peerClosed()deferred behind the queue for collected peers too, which left a'close'-listening port with an unread message pinned forever, andtryTakeMessage()read its own queue before the peer's state (a worker'spostMessage(); close()landing in between dropped the message). Both fixed in f0af4bc.start()ed port without a listener (aref()'d one hung), an idle port whose peer was collected was never told even after it added a'close'listener (pinned),peerClosed()'s flush dispatched past aonce()handler, andpostMessage()on the now-closed port no longer consumed the ports in its transfer list. All fixed in d2851de, each with a test that fails on f0af4bc.start()only turned receiving on the first time it ran, sostart()on a paused port left the close on hold (aref()'d one hung). Fixed in 5db54a9, with a test for both orders relative to the peer's close.