bundler: route every cross-thread event to the bundle thread through one post() - #37997
bundler: route every cross-thread event to the bundle thread through one post()#37997alii wants to merge 8 commits into
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WalkthroughChangesThe bundler adds typed post events for parse completion and plugin load/resolve callbacks. JS and mini event-loop dispatch now use the shared Typed post-event completion
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LGTM — unifies the JS-loop and mini-loop defer-notify paths so load.deferred is set on both.
What was reviewed:
- Checked
Loadlifetime on the JS-loop path: arena-allocated, linked inoutstanding_loadsuntilon_load, and the plugin awaits the defer promise before its onLoad can complete — same guarantee the mini path already relies on for the identical*mut Loadpost. - Confirmed no other callers of the removed
on_notify_defer(&mut self)/on_notify_defer_mini;thread_lock.assert_locked()is preserved in the merged fn. Posted::Refusedbehavior unchanged: notify never runs,deferredstays false, sweep handles it as before.
Extended reasoning...
Overview
The PR merges BundleV2::on_notify_defer and on_notify_defer_mini into a single on_notify_defer(load, this) that sets load.deferred = true alongside the deferred_pending counter bump. The JS-loop path in Load::on_defer now posts *mut Load (instead of *mut BundleV2) via ConcurrentTask::from_callback, and the callback derefs load.bv2 to reach the bundler. The mini-loop wrapper is updated to call the merged function. Net: two functions become one, and a latent state divergence (flag not set on the JS-loop path) is closed.
Security risks
None. This is internal bundler bookkeeping — no user-controlled input reaches the changed lines, and the pointer being posted was already flowing through the sibling mini-loop path.
Level of scrutiny
Medium. The change touches an unsafe deref of a raw pointer that crosses an async task boundary, which is exactly the memory-safety category the repo review rules flag hardest. But the new JS-loop shape is a direct mirror of the existing mini-loop path at JSBundler.rs:1540, which already passes std::ptr::from_mut::<Load>(self) across the same boundary via enqueue_task_concurrent_with_extra_ctx. The SAFETY comment in on_notify_defer_raw states the invariant (arena-allocated, linked in outstanding_loads until on_load, which can only fire after this notify), and I verified it against bundle_v2.rs:1267 (push into outstanding_loads in run_on_js_thread), :4419 (unlink in on_load), and the defer-promise ordering in append_defer_promise. Ordering on the JS-loop path is additionally guaranteed because both tasks post FIFO to the same event loop and the plugin's onLoad awaits the defer promise.
Other factors
The PR description is precise about why this is latent (the cancellation sweep at bundle_v2.rs:2120 and the drain at Graph.rs:230 are the only readers of load.deferred, and the sweep runs only for mini-loop bundles today), so no new test can distinguish before/after — the existing test/bundler/bundler_defer.test.ts covers both paths. Grep confirms no other callers of the removed signatures. The Posted::Refused branch is unchanged in effect: the notify never runs, deferred stays false, and the sweep treats it as a non-deferred outstanding load, same as before.
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LGTM — collapses the two notify-defer paths into one so load.deferred is set on the JS-loop path too.
Checked that the new *mut Load payload on the JS-loop ConcurrentTask is the same pattern the mini-loop already used (arena-allocated Load, unit still in pending_items until this task runs, load.bv2 deref goes through the existing bv2_mut helper). Verified no other callers of the old on_notify_defer(&mut self) remain, and that the two consumers of load.deferred (fail_outstanding_plugin_requests and drain_deferred_tasks) are unaffected in semantics. The Posted::Refused arm is unchanged — the callback still doesn't run, same as before. New dev-server test drives the JS-loop defer path that previously had no coverage.
Extended reasoning...
Overview
Two source files touched. In bundle_v2.rs, on_notify_defer(&mut self) and on_notify_defer_mini(load, this) are folded into a single on_notify_defer(load, this) that sets load.deferred = true alongside the existing deferred_pending += 1; decrement_scan_counter(). In JSBundler.rs, the JS-event-loop arm of Load::on_defer now posts *mut Load (instead of *mut BundleV2) to ConcurrentTask::from_callback, and on_notify_defer_raw derefs it and reaches bv2 via load.bv2. A dev-server test in test/bake/dev/plugins.test.ts exercises args.defer() from an onLoad plugin under the dev server (JS loop), which was previously untested.
Security risks
None. No user-controlled input parsing, no auth/crypto/permissions.
Level of scrutiny
Moderate — this is unsafe pointer plumbing in the bundler, which the review guidelines flag as high-signal. But the change is very small and strictly aligns the JS-loop arm with the mini-loop arm that already carried *mut Load and dereferenced it under the same lifetime argument (arena-allocated Load, bundle held alive by the load's own scan-counter unit). The load.bv2 deref goes through the pre-existing bv2_mut() helper whose safety doc already covers on_notify_defer_raw. The new SAFETY comment is accurate: Load sits in outstanding_loads from dispatch() until on_load runs, and on_load cannot run before this notify because the plugin is awaiting the defer promise, which only resolves after drain_deferred_tasks — which in turn requires pending_items == 0, blocked by this load's own unit until on_notify_defer moves it.
Other factors
- Confirmed via grep that no callers of the removed
on_notify_defer(&mut self)overload remain anywhere insrc/. ConcurrentTask::from_callbackis generic overT, so switching the payload type fromBundleV2toLoadis a straight type substitution.- The
Posted::Refusedbranch (VM torn down mid-bundle) still just releases the task; no counter/flag is touched, same as before. - Both readers of
load.deferred— the cancellation sweep atbundle_v2.rs:2123and the drain walk atGraph.rs:237— are semantically unaffected: the sweep doesn't fire for dev-server bundles today (no completion to cancel), and the drain resets the flag to the same value the old JS-loop path implicitly left it at. - The test follows the existing
devTestconventions in the file (same fixture shape as the neighbouring onLoad test) and asserts the observable defer contract (otherLoaded === trueby the time the deferred load returns), plus an incremental rebuild round-trip. - The bug-hunting pass found nothing.
- A duplicate-PR bot flagged #37731 as covering the same change; that's a process matter for the author, not a correctness concern here.
alii
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Actionable comments posted: 2
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Inline comments:
In `@src/bundler/bundle_v2.rs`:
- Around line 4360-4374: Prevent the same Load from being enqueued through both
PluginLoadDeferred and PluginLoadSettled when defer() and an onLoad result occur
before event processing; update the runOnLoadPlugins/event scheduling flow so
the deferred event is drained before settlement, or assign separate intrusive
queue nodes. Add a regression test covering an onLoad callback that calls
defer() and returns contents.
In `@src/bundler/post.rs`:
- Around line 68-78: Update MiniEventLoop::Drop to drain both task queues during
teardown before asserting they are empty, and invoke the appropriate refusal
cleanup for each queued task so non-owning raw pointers and heap::into_raw
allocations are released through ParseComplete::refused.
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Fix all unresolved CodeRabbit comments on this PR:
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📒 Files selected for processing (6)
src/bundler/ParseTask.rssrc/bundler/ServerComponentParseTask.rssrc/bundler/bundle_v2.rssrc/bundler/lib.rssrc/bundler/post.rssrc/runtime/api/JSBundler.rs
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Updated 10:05 PM PT - Aug 14th, 2026
❌ @alii, your commit 520fde1 has some failures in 🧪 To try this PR locally: bunx bun-pr 37997That installs a local version of the PR into your bun-37997 --bun |
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@robobun adopt |
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@robobun get this mergeable |
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✅ Mergeable and ready for a maintainer: main merged in, all review threads resolved, and a source lint (eab126a) pins the one-dispatch-site invariant. On the current head (520fde1) every CI lane that has run is green (177 jobs); the only two jobs outstanding are darwin 14 aarch64 test shards that keep expiring before any agent picks them up, which is lane capacity, not this change. The earlier Windows x64 segfault in bake/deinitialization symbolizes to a bun-usockets teardown double free unrelated to this PR (details in the PR body); it is filed separately. |
# Conflicts: # src/runtime/api/JSBundler.rs
LinkerContext::any_loop_mut took &self (with a clippy allow) so worker threads could reach the loop through a shared backref; post() reads the field raw now and the one remaining caller has &mut self, so give it the normal receiver. JSBundler's bv2_mut only served bv2_plugin, which now reads the plugins field through the raw pointer instead of forming a &mut BundleV2 on the JS thread. Drop the #[allow(non_snake_case)] that was attached to the deleted EventLoop module, and update the comments that still named on_complete, on_load_async/on_resolve_async, the old any_loop_mut callers, or a free of the ServerComponentParseTask that does not happen.
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I re-reviewed after cf1ef56 and found no new issues — that commit addressed all the earlier doc-comment/dead-code nits (stale any_loop_mut/on_complete references, orphaned #[allow(non_snake_case)], Resolve.task doc, bv2_mut caller list). Given this reworks the bundler's cross-thread unsafe dispatch (raw addr_of! reads of BundleV2 fields from other threads, intrusive offset_of! queue nodes, the new Event trait), a human pass on the concurrency/ownership story in post.rs and the bv2_plugin change is still worthwhile.
Checked: post() preserves the prior per-loop dispatch semantics for all four events; ParseComplete::refused matches the old JS-loop Posted::Refused cleanup; PluginLoadDeferred and PluginLoadSettled sharing Load.task as their queue node is fine because a load defers at most once and the drain runs before settlement re-posts it; the &self → &mut self change on LinkerContext::any_loop_mut compiles at both remaining call sites; no stale references to the deleted on_*_async/on_notify_defer* remain in src/.
Extended reasoning...
Overview
The PR consolidates five hand-rolled "which loop is the bundle running on?" match sites (parse-worker completion ×2, plugin resolve/load settled, plugin defer) into one bundler::post module: an Event trait with Item/NODE/bundle()/run()/refused(), and one unsafe fn post<E>() that reads linker.r#loop and js_poster via addr_of! and enqueues on either the JS loop (ConcurrentTask::from_callback) or the Mini loop (enqueue_task_concurrent_with_extra_ctx). Four Event impls — ParseComplete, PluginLoadSettled, PluginResolveSettled, PluginLoadDeferred — replace ~10 free-function callbacks. The follow-up commit cf1ef56 tightens LinkerContext::any_loop_mut to &mut self (drops the clippy::mut_from_ref allow), deletes bv2_mut in favor of a raw addr_of!((*bv2).plugins) read in bv2_plugin, and prunes the stale doc comments the earlier review flagged. It also fixes parse_task::Result.task's type to AnyTaskWithExtraContext (the field was declared as the larger ConcurrentTask but written as the smaller type), and adds a bake dev-server defer() test.
Security risks
None. No user-input parsing, no auth/crypto, no external I/O. This is internal thread-hop plumbing between the bundle thread and worker/JS threads.
Level of scrutiny
High. This is memory-safety-critical: unsafe cross-thread dispatch with raw pointers into an arena-owned BundleV2, intrusive queue nodes located by offset_of!, and a subtle change to how the JS thread reads BundleV2 fields (addr_of! on individual set-once fields instead of forming &mut BundleV2). REVIEW.md's "know the thread affinity of every line" and "never let a pointer outlive the memory" both apply directly. The refactor is well-motivated (five drifting duplicates → one dispatch point) and the diff reads correctly to me — each new Event::run is line-for-line the body of the deleted per-loop callback pair, and the SAFETY comments state the actual invariants — but the surface area of unsafe changed here is more than I'd auto-approve.
Other factors
All five earlier inline nits from this bot were resolved in cf1ef56. The one behavior change (Load.deferred = true now set on the JS-loop path too) is covered by the new test/bake/dev/plugins.test.ts case; the PR description says the bundler plugin/defer/loader/edgecase suites and bake plugin tests were run on the debug build. The two CodeRabbit comments (Mini-loop teardown leak of queued Results; shared Load.task node between defer/settle) describe pre-existing conditions the refactor doesn't change — the Mini loop already asserted empty on drop, and defer/settle already shared the node with the same drain-before-settle ordering.
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I re-reviewed after cf1ef56 and found no issues — all five earlier nits are addressed and the two coderabbit threads are resolved with the pre-existing-behavior rationale. Given this reworks the bundler's cross-thread event dispatch (raw addr_of! reads of BundleV2 from worker/JS threads, intrusive-node ownership, the ParseComplete free path), a human pass is still worth having.
What was reviewed:
post()'s raw reads oflinker.r#loop/js_poster/plugins— confirmed each is written once atBundleV2::initand never again.- No stale references to the deleted
on_complete/on_*_async/on_notify_defer*/*_minihandlers remain undersrc/bundler. ParseComplete::run's dealloc-without-Drop path matches the two paths it replaced;refusedcorrectly runs full Drop instead.PluginLoadDeferred::NODE = PluginLoadSettled::NODEpreserves the pre-PR shared node; the un-awaited-defer fix is deferred to #37731 as stated.
Extended reasoning...
Overview
This PR consolidates the bundler's cross-thread event delivery. Previously five call sites each open-coded a match AnyEventLoop { Js => …, Mini => … } with a separate handler per arm (10 handlers total); those are replaced by a single post::<E>() in the new src/bundler/post.rs and four Event impls (ParseComplete, PluginLoadSettled, PluginResolveSettled, PluginLoadDeferred). Along the way it fixes Result.task's declared type, deletes bv2_mut in JSBundler.rs in favor of a raw addr_of! field read, tightens LinkerContext::any_loop_mut to &mut self, adds a dev-server defer() test, and adds a source-lint test that keeps the AnyEventLoop match confined to post.rs. Net −70 lines. The follow-up commit cf1ef56 addressed all five doc/dead-code nits from my earlier passes plus the coderabbit threads.
Security risks
None identified. This is internal bundler plumbing; no user input parsing, auth, or crypto is touched.
Level of scrutiny
High. The change is almost entirely unsafe: it forms &mut BundleV2 on the bundle thread from a raw backref, reads three BundleV2 fields via addr_of! while another thread may hold &mut to the rest of the struct, and reshapes the ownership/free path for heap-allocated parse_task::Result. The SAFETY comments are thorough and the refactor is a strict deduplication of existing logic (I diffed each Event::run against the pair of handlers it replaces), and I verified the write-once claim for linker.r#loop/js_poster/plugins by grepping for assignments — each is set exactly once at init. But this is precisely the class of change (cross-thread lifetime, intrusive queue nodes, raw-pointer field reads under concurrent &mut) where a maintainer's eyes are warranted, and REVIEW.md flags cross-thread lifetime and &mut-aliasing as the most-blocked category.
Other factors
A maintainer (alii) is already actively shepherding the PR. The robobun CI comment noted a Windows x64 segfault in test/bake/deinitialization.test.ts on the pre-cf1ef56 build, with CI for cf1ef56 still running at the time; whether that is related to this change or pre-existing flake is worth confirming before merge. The added dev-server defer() test and the source-lint test are both reasonable and follow harness conventions.
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I reviewed the latest revision (post-cf1ef56/eab126a/520fde16) and found no bugs; all earlier nits are addressed and resolved. Because this refactors the bundler's cross-thread dispatch — new unsafe code in post.rs that reads linker.r#loop/js_poster via raw pointers while the bundle thread may hold &mut BundleV2, plus the bv2_plugin rewrite that avoids forming &mut BundleV2 on the JS thread — a human look at the soundness argument is still worthwhile.
What was reviewed:
post::<E>()dispatch: rawaddr_of!reads of write-once fields, both loop arms, and therefusedpath vs. the old per-site handling — behavior matches.ParseComplete::run/refused: the dealloc-without-Drop path is preserved from the two old copies;refusedcorrectly uses full Drop since nothing was swapped out.PluginLoadDeferrednow setsload.deferredon both loops (the one intentional behavior change);NODEaliasing withPluginLoadSettledis pre-existing and left to #37731.- The source-lint test's comment-stripping and
tracked/realpathguards, and the new bake devdefer()test's assertion shape.
Extended reasoning...
Overview
This PR consolidates five hand-written cross-thread dispatch sites in the bundler (parse completion ×2, plugin resolve/load settled, plugin defer()) into a single post::<E>(item) function backed by an Event trait. Each event now has one run() regardless of whether the bundle runs on the owning VM's JS loop (bake/dev server) or its own mini loop (Bun.build, bun build). Files touched: src/bundler/{post.rs (new), ParseTask.rs, ServerComponentParseTask.rs, bundle_v2.rs, LinkerContext.rs, lib.rs}, src/runtime/api/JSBundler.rs, plus a new bake dev-server defer() test and a source-lint test that pins post.rs as the sole matcher on AnyEventLoop::Js / caller of enqueue_task_concurrent_with_extra_ctx in bundler code.
Along the way it fixes Result.task's declared type (was ConcurrentTask, actually held AnyTaskWithExtraContext), deletes bv2_mut (its &mut BundleV2 on the JS thread was unsound while the bundle thread also holds &mut), tightens LinkerContext::any_loop_mut to &mut self now that worker-thread callers are gone, and updates ~a dozen doc comments that named the deleted machinery.
Security risks
None. No user-facing input parsing, no network/auth/crypto surface. The concern class here is memory safety and data races (Rust unsafe), not security.
Level of scrutiny
High. The new post() is a small function but it is entirely unsafe: it reads two fields of *bv2 through raw pointers from a thread that does not own *bv2, forms &mut AnyEventLoop from a backref that another thread may be ticking, and relies on trait-level contracts (Event::NODE, Event::bundle) for the intrusive queue node offset and lifetime. The SAFETY arguments look correct — both fields are write-once in BundleV2::init, both loop enqueue paths are MPSC-safe, and the mini-loop node write lands inside caller-owned *item — but this is exactly the kind of concurrency-sensitive refactor the repo's review guidance flags for a human pass. The bv2_plugin change similarly trades a &mut BundleV2 (unsound aliasing) for a raw-pointer field read, which is an improvement but changes the aliasing model.
Other factors
- All seven prior review threads (five of mine, two from CodeRabbit) are resolved; cf1ef56 addressed every nit and the diff now reflects those fixes.
- The one intentional behavior change (
Load.deferred = trueon the JS-loop path too) is covered by the new bake dev test; the sharedLoad.tasknode between defer and settle is documented as pre-existing and deferred to #37731. - The Windows x64 CI flake in
test/bake/deinitialization.test.tsis credibly unrelated per the PR description's symbolized stack. - Net -70 lines with a source-lint that fails on main and passes here, so the abstraction is enforced going forward.
Given the unsafe-heavy cross-thread nature and that this is a new abstraction (per REVIEW.md, "new cross-cutting abstractions need maintainer agreement"), deferring to a human reviewer rather than auto-approving.
2 participants
The bundle thread runs on one of two event loops: the owning VM's JS loop (dev server) or its own mini loop (
Bun.build,bun build). Every event another thread posts to it (a parse finished, a plugin resolve/load settled, adefer()) picked the loop at its own call site, with a separate handler per loop: five sites, ten handlers, nothing keeping each pair in step.defer()had already drifted (it set a flag on the mini-loop path only; harmless today because nothing reads it on the other path yet).Now there is one
post()and each event is one type with onerun();post()is the only place that looks at which loop is in use. Four event types replace the ten handlers, about 70 lines go away, and a source lint test fails CI if a sixth hand-written dispatch appears in the bundler.No behavior change beyond the drifted flag now being set on both paths. Two small things fell out: a parse-result free path that was written twice, and a task field declared as one type with a larger one written into it (worked by size luck).
Ran the bundler plugin/defer/loader/edge-case tests and the bake dev plugin tests on a debug build; added a dev-server
defer()test, which that path did not have.[review] gate passed · iteration 1 · 9 files touched
fails on main (without fix)
passes on PR (with fix)
diff hotspot
gate history · 1 passed · 1 rejected · iteration 1
evidence per changed file
The Windows x64 segfault in
test/bake/deinitialization.test.tson the cf1ef56 build (#94863) is not this PR: symbolized against that build's pdb, the crash isus_poll_start_rc(bun-usocketseventing/libuv.c:243) understart_connections/us_internal_socket_after_resolve, a client connect for the next test case hitting a block the previous case's socket teardown had freed twice. No bundler frame is on the stack, and the same fixture already flakes on main on Windows (a hang in build 94142). Filed separately.