Bump WebKit (oven-sh/WebKit#674 preview): the microtask queue no longer aborts at 2^25 pending jobs - #42903
Bump WebKit (oven-sh/WebKit#674 preview): the microtask queue no longer aborts at 2^25 pending jobs#42903robobun wants to merge 3 commits into
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…grows past 2^25 pending jobs The microtask queue is a WTF::Deque, and a Deque buffer was limited to 2^31 - 1 bytes, so the 2^25th pending job aborted the process. oven-sh/WebKit#674 lifts that limit for this Deque. The pin is the current WebKit commit (c28156899e5f) plus that change. The new test queues 2^25 + 1 queueMicrotask() callbacks in a child process and checks that all of them run.
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Status: reproduced on 1.4.3 canary ( const f = () => {};
for (let i = 0; i < 33554431; i++) queueMicrotask(f);The process exits 134 with The engine fix is oven-sh/WebKit#674. This PR pins its preview build and adds a test to This PR is a draft until oven-sh/WebKit#674 merges. Then the pin moves to the |
WalkthroughThe change pins WebKit to an autobuild preview for issue ChangesMicrotask queue validation
Priority: ➖ Normal Severity of issue fixed: Medium Merge Risk: 🟡 Moderate · up to The stress test can retain a stalled debug or ASAN CI worker for up to five minutes despite the suite’s existing timeout handling. Remove the per-test timeout before merging. 🚥 Pre-merge checks | ✅ 4✅ Passed checks (4 passed)
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Inline comments:
In `@scripts/build/deps/webkit.ts`:
- Line 6: Retain the current WEBKIT_VERSION preview pin while WebKit PR 674
remains open; do not change process.versions.webkit or add a separate update.
After the preview release is deleted following merge, replace WEBKIT_VERSION
with the merged autobuild SHA tag.
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On the review above:
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…wn on ASAN and debug builds The gate was totalmem() >= 8 GiB, and an 8 GiB Linux agent reports a little less, so the main Linux lanes skipped the test. The child needs about 3 GB, so the gate is 6 GiB now. The x64-asan lane needed 48 s of its 60 s timeout, most of it to run 2^25 callbacks. ASAN and debug builds now exit when the queue has grown past 2^25 tasks, which is where the abort was. Release builds still check that every callback runs.
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Thanks for the review. All three findings were correct, and the CI run of the first push (build 116453) confirmed two of them with numbers. e0a8ed6 addresses them, and each thread has the details.
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Inline comments:
In `@test/js/web/timers/microtask.test.js`:
- Line 84: Correct the comment near the pending-task limit to refer to
WTF::Deque instead of WTF::Vector, preserving the existing explanation and test
behavior.
- Line 119: Remove the per-test timeout value from the slowBuild conditional in
the microtask test, relying on Bun’s existing test timeout behavior instead.
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…timeout to debug builds The queue is a WTF::Deque, and the 2 GB limit is the limit of the Vector buffer that the Deque uses. The comment now names both. With the short form of the test the x64-asan lane needs 4 s, so ASAN builds use the same 60 s timeout as release builds. Only debug builds, which CI does not run, need more (45 s measured).
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Updated 4:43 AM PT - Sep 16th, 2026
✅ @robobun, your commit bee7d96a7384f1f13285a84c2e6dbab5e267876a passed in 🧪 To try this PR locally: bunx bun-pr 42903That installs a local version of the PR into your bun-42903 --bun |
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On the review of e0a8ed6, both threads have replies:
The same build shows that the 6 GiB gate works: debian 13 x64 now runs the test (3 pass, 2.5 s) where it skipped before. |
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Problem
panic(main thread): abort() called, exit 134, also insidetry/catch.for (let i = 0; i < 33554431; i++) queueMicrotask(f)does it after 1.6 s. Node v26 queues and drains the same count. A fuzzing run found it, and it is not a regression. This is the microtask queue section of Script-sized containers that still abort the process when they cannot grow: the microtask queue and the web streams request queues #42648.WTF::Dequein the WebKit fork. A Deque doubles one buffer, WTF limits a buffer to 2^31 - 1 bytes, and 2^26 tasks of 40 bytes is past that, so the growth callsCRASH().Fix
RangeErroris not possible: most jobs come from paths that cannot throw, such as a promise that settles and queues one job per reaction.c28156899e5fplus that change). It is a draft until [JSC] The microtask queue aborts the process at 2^25 pending tasks WebKit#674 lands, because a preview release goes away when its PR closes. Then I move the pin to the merge commit'sautobuild-<sha>.test/js/web/timers/microtask.test.js. A child queues 2^25 + 1 callbacks, and release builds check that all of them run. It fails on a debug build of main (exit 134) and passes with the pin.Background
queueMicrotask()callback.scripts/build/deps/webkit.tsnames. A WebKit pull request publishes a preview build asautobuild-preview-pr-<n>-<sha8>.Notes
Other ways to reach the same abort, all fixed by the same change:
p.then(f)2^25 times on a settled promise.resolve()of a promise that has 2^25 reactions. Attaching them is free, the abort is inresolve().Promise.race(a)orPromise.all(a)witha.length = 4e7.WritableStreamwith 2^25 pendingwriter.write()promises that errors:writableStreamFinishErroring(src/jsc/bindings/webcore/streams/WritableStreamOperations.cpp:340) rejects them in one loop.Also ran with the pin, on a debug build: the node microtask tests (
test-microtask-queue-*.js,test-queue-microtask.js),bun-jsc.test.tsandstreams.test.js.The test:
totalmem() >= 6 GiB. The child peaks at 2.9 GB: the 2.7 GB buffer for 2^26 tasks, of which it touches half, and the old 1.3 GB buffer while the Deque copies. An 8 GiB Linux agent reports a little less than 8 GiB, and the runner does not run this file in parallel with other tests.Self-review: I first built a queue of fixed-size segments (oven-sh/WebKit#667, closed). The review found that too large for this abort: it replaces the container on the path of every
await. The byte-limit change is the narrow fix. What it leaves as it was: the Deque holds the old and the new buffer while it grows, and it never gives the buffer back.[policy-decision:webkit] gate passed · iteration 0 · 2 files touched
passes on PR (with fix)
diff hotspot
gate history · 3 passed · 0 rejected · iteration 0
evidence per changed file