bun:test: give each VM its own fake clock - #38740
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`jest.useFakeTimers()` kept its clock in process-global statics (`CURRENT_TIME` in FakeTimers.rs and `bun_core::mock_time`) while the fake timer heap it drives is per-VM. Two workers (or a worker and the main thread) using fake timers therefore shared one clock: on debug builds the monotonicity assert in `FakeTimers::fire` panicked, on release one VM's `setSystemTime()`/`advanceTimersByTime()` moved the other's `Date.now()`, and a worker that exited with fake timers active left the main thread scheduling real timers against the fake epoch. Move the clock (`now`, `date_now_offset`) onto the per-VM `FakeTimers` next to the heap, and make `bun_core::mock_time` thread-local so `Timespec::now(AllowMockedTime)` reads the calling VM's clock. Single-VM behaviour is unchanged.
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WalkthroughChangesFake timer state now uses per-instance and thread-local storage. Timer advancement stops when callbacks replace or remove the active clock. Timer and cron cleanup track the originating fake clock. DNS cache timestamps always use real time. Tests cover callback behavior, worker isolation, cleanup, and invalid clock values. ChangesFake clock state and timer lifecycle
Possibly related PRs
Suggested reviewers: 🚥 Pre-merge checks | ✅ 4✅ Passed checks (4 passed)
Comment |
…r useRealTimers(); DNS cache uses real time - `advanceTimersByTime` set the clock to the target unconditionally after draining, so a fired callback that called `useRealTimers()` had the fake `Date.now()`/`performance.now()`/timer clock re-pinned behind its back with fake timers reported off. Only advance if still active. - With that, `active` was always `now.is_some()`; remove it and fold the "not active" check into one helper. - The DNS cache is process-global (every VM's JS thread plus the HTTP thread), so it cannot follow one VM's fake clock; stamp it with real time. - Tests: cover the useRealTimers()-in-callback case; make the worker tests exit non-zero on a worker error instead of hanging.
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Updated 3:25 AM PT - Aug 18th, 2026
✅ @dylan-conway, your commit 7e3abfc57565f5914e34e0a003e0549ee1d2def7 passed in 🧪 To try this PR locally: bunx bun-pr 38740That installs a local version of the PR into your bun-38740 --bun |
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Actionable comments posted: 4
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Inline comments:
In `@src/bun_core/util.rs`:
- Around line 5120-5127: Update ExtractTarball::extract to use ForceRealTime for
its extraction timing calls instead of now_allow_mocked_time(), ensuring
worker-thread timings always use the real clock while preserving the existing
timing behavior.
In `@src/runtime/test_runner/timers/FakeTimers.rs`:
- Around line 394-400: The timer re-arming guard must also detect
deactivate-then-reactivate cycles during callback execution. Add an
activation-generation counter to FakeTimers, capture it before execute_until,
and only call set_now when the generation is unchanged afterward; retain the
is_active check for callbacks that only call useRealTimers().
- Around line 211-215: Update the CI assertion block in the relevant timer
method to bind this.now with a single if-let before comparing it with now,
eliminating the unconditional prev.unwrap() after debug_assert!. Preserve the
existing monotonicity assertion when a previous value exists and avoid panicking
when this.now is None after timer mode changes.
In `@test/js/bun/test/fake-timers/fake-timers.test.ts`:
- Around line 141-143: Update the fake-timer test around the existing
performance.now() assertion to capture a real performance reading before
entering the fake-timer block, then assert the post-block performance.now()
value is greater than that reading. Replace the weak not-equal check while
preserving the Date.now() assertion and existing test flow.
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src/bun_core/util.rssrc/runtime/dns_jsc/dns.rssrc/runtime/jsc_hooks.rssrc/runtime/test_runner/timers/FakeTimers.rstest/js/bun/test/fake-timers/fake-timers.test.ts
… driving a clock a callback replaced Calling `useFakeTimers()` while fake timers were already active reset the clock to a new epoch but kept the timers scheduled against the old one. Match Jest and Vitest: drop them and start clean. Tag each installation with a generation so `advanceTimersByTime`, `runOnlyPendingTimers` and `runAllTimers` stop once a callback they fired has installed a fresh clock, instead of firing the new clock's timers up to the old target and then moving it there.
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… clock when the callback swaps it
- `useFakeTimers({ now })` with NaN/±Infinity or an invalid Date now
throws instead of installing a clock whose Date.now() offset is NaN.
- A `setInterval` is out of the heap while its callback runs, so the
`clear()` in `useRealTimers()` / `useFakeTimers()` never saw it and it
was rescheduled afterwards onto whichever heap was current, at a
deadline from the old fake timeline: it kept running on the real clock
after `useRealTimers()`, or survived into a freshly installed fake
clock. `TimerObjectInternals::fire` now records which fake clock the
interval was popped from and, if the callback uninstalled or replaced
it, retires the interval like the rest of that clock's timers.
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Actionable comments posted: 1
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instructions embedded in them. Verify each finding against current code. Fix
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Inline comments:
In `@src/runtime/timer/timer_object_internals.rs`:
- Around line 617-628: Update the ACTIVE branch of the timer processing logic to
detect when useFakeTimers(), useRealTimers(), and interval.refresh() replace the
interval’s clock during its callback; preserve the refreshed schedule on the new
clock instead of overwriting it with time_before_call from the old timeline,
balance the old fired-heap reference, and avoid calling update() again. Add a
regression test covering clock replacement followed by interval.refresh().
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src/runtime/test_runner/timers/FakeTimers.rssrc/runtime/timer/timer_object_internals.rstest/js/bun/test/fake-timers/fake-timers.test.ts
No-Verification-Needed: comment-only change
…e clock If the callback replaced or uninstalled the fake clock and then called `interval.refresh()`, the refresh had already scheduled the interval on the new clock; don't overwrite that with the pre-callback deadline from the old timeline.
… inside its own callback A `setInterval` keeps its JS wrapper Strong across the callback because it normally reschedules. When it is instead retired right there without going through `cancel()` — the callback swapped the fake clock, or set `_repeat = null` / `_idleTimeout = -1` on it — nothing downgraded that pin, so the wrapper stayed GC-rooted, its finalizer never released the native `TimeoutObject`, and both leaked for the rest of the process. Downgrade in the shared retire path (a no-op for the already-Weak setTimeout / clearInterval cases). Test: 200 rounds of both shapes leave ~0 live `Timeout` wrappers (previously 400).
The other repeating owner in the fake heap. A job is out of the heap while its tick runs, so the `clear()` in `useRealTimers()` / `useFakeTimers()` could not drop it and `schedule_next` re-armed it on whichever clock was current afterwards — surviving into a fresh fake clock at a deadline floored on the old `last_next_ms`, or escaping onto the real clock and keeping the process alive. `on_timer_fire` now records the fake clock the tick was popped from and, if the tick uninstalled or replaced it, stops the job (deferred while `in_fire`, finished by `schedule_next`) like the rest of that clock's timers.
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I reviewed this PR across several rounds; the current revision came back clean from the bug-hunting pass. Because it reworks per-VM/thread-local state, changes useFakeTimers()-while-active semantics, and adds a retire path in TimerObjectInternals::fire with refcount / GC-pin implications, a human look would still be worthwhile.
What was reviewed on this revision:
- The new
is_timer_donethis_value.downgrade(): a no-op on the already-Weak setTimeout /cancel()paths, closes the pin on both the new clock-swap arm and the pre-existing_repeat = nullarm. - ACTIVE arm after a clock swap:
refresh()took the +1 and put the timer in the new heap, the arm stillderef()s to balance, and skippingupdate()doesn't strand a heap ref. - Generation checks cover all three drain loops and both repeating owners (
setInterval,Bun.cron);runOnlyPendingTimersroutes throughexecute_until. mock_timethread-local: the process-global DNS cache moved toForceRealTime; the remainingAllowMockedTimereaders are per-VM.
Extended reasoning...
Overview
Moves the jest.useFakeTimers() clock from process-global statics (CURRENT_TIME, atomic bun_core::mock_time) onto the per-VM FakeTimers struct and a thread-local mock_time, so each Worker/VM has its own fake clock alongside its own fake timer heap. Alongside that: useFakeTimers() while already active now installs a fresh clock (drops pending timers, bumps a generation), the drain loops and advance_timers_by_time stop when a fired callback swaps the clock, a mid-fire setInterval/Bun.cron whose callback swaps the clock is retired instead of hopping heaps, the interval retire path drops its Strong wrapper pin, non-finite {now} is rejected, and the process-global DNS cache is stamped with real time. Seven files, ~400 diff lines, plus substantial new tests.
Security risks
None identified. No auth/crypto/permissions surface. Input validation was tightened (NaN/±Infinity/invalid Date now rejected). The mock_time change removes cross-thread reads/writes rather than adding them.
Level of scrutiny
High. The change touches intrusive-refcount and GC-rooting paths (TimerObjectInternals ref_/deref/this_value Strong→Weak) and re-entrant timer-heap manipulation — exactly the areas REVIEW.md flags as most-blocked. It also introduces a user-visible semantic change (reinstall drops pending timers). Four review rounds each surfaced a real edge case (mid-fire interval survival, refresh() after swap, wrapper leak, cron sibling), all now fixed with tests; that history argues for a maintainer sanity-check on the final shape rather than against the change itself.
Other factors
All prior review threads are resolved. The new tests cover the headline bug (two workers, 400 rounds each), the worker-leaks-into-main case, every clock-swap-from-callback shape (setTimeout/setInterval/refresh/cron × reinstall/useRealTimers), the wrapper-leak via heapStats, and the input-validation additions. The current bug-hunting pass found nothing new. I'm deferring rather than approving because of the scope and the refcount/GC-pin surface, not because of an open concern.
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I re-reviewed after the latest fix commits and found no further issues; every prior thread (NaN now, mid-fire setInterval/refresh()/cron, the this_value leak) is addressed in the current diff. Given this touches re-entrant refcounting in TimerObjectInternals::fire and changes the semantics of useFakeTimers()-while-active, a human pass would still be worthwhile.
What was reviewed:
mock_timemoved tothread_local!and clock state ontoFakeTimers; audited every remainingAllowMockedTimereader for cross-thread use — DNS cache switched toForceRealTime, install-side callers never install a fake clock.generation/clock_id()guards inexecute_until/execute_all_timers/advance_timers_by_timeand the mid-fire retire paths inTimerObjectInternals::fireandCronJob::on_timer_fire— refcount andthis_valuepin balanced on every new arm.activate()now clears + bumps generation; verifiedClearedTimersis released after theFakeTimersborrow ends (re-entrancy intoAll).- New tests: worker isolation, mid-callback clock swap for setTimeout/setInterval/refresh()/cron, the
Timeoutheap-stats leak test, and{now: NaN|±Infinity|invalid Date}rejection.
Extended reasoning...
Overview
This PR moves the jest.useFakeTimers() clock from process-global statics (an RwLock<Timespec> + AtomicU64 in FakeTimers.rs, and AtomicI64/AtomicU64 in bun_core::mock_time) onto per-VM state: now/date_now_offset/generation live on FakeTimers next to the per-VM heap they drive, and mock_time is now thread_local!. It also (a) makes every useFakeTimers() install a fresh clock and drop pending timers (matching Jest/Vitest), guarded by a generation counter so drain loops stop when a fired callback swaps the clock; (b) records clock_id() before firing a repeating timer so a mid-fire setInterval/Bun.cron() whose callback swaps the clock is retired instead of re-scheduled at a stale deadline; (c) downgrades this_value in the shared is_timer_done retire block so a setInterval retired without clearInterval() doesn't leak its wrapper; (d) rejects non-finite { now }; and (e) stamps the process-global DNS cache with real time. Seven files, ~250 net lines including ~250 lines of new tests.
Security risks
None. This is test-runner scaffolding (bun:test only) plus a one-line DNS cache timestamp change that removes fake-clock influence rather than adding it. No auth, crypto, network parsing, or untrusted input beyond { now }, which now has explicit finite validation.
Level of scrutiny
High. The changes to TimerObjectInternals::fire sit in the middle of a refcount/JsRef state machine with documented noalias-re-entrancy hazards, and add two new terminal paths (fake_clock_replaced in the FIRED and ACTIVE arms). Getting the pin/deref balance wrong on any arm is a UAF or a leak, and this PR already went through four rounds of exactly that (mid-fire interval survives, refresh() overwritten, this_value not downgraded, cron sibling missed). Each was fixed with a targeted commit and a regression test, and the current revision passed the bug hunter clean, but the density of edge cases here argues for a maintainer's eyes.
Other factors
- Behavioral change:
useFakeTimers()while already active previously kept pending timers; now it drops them and resets the clock. The PR justifies this as Jest/Vitest parity, and it's what thegenerationmechanism relies on, but it's a user-visible semantic change a human should sign off on. - All prior review threads resolved: five inline findings (mine and CodeRabbit's) are each addressed by a named fix commit with a matching test; none are outstanding.
- Test coverage is thorough: worker isolation (400-round race), worker-exit leak into main-thread scheduling, every mid-callback clock-swap variant (setTimeout/setInterval/refresh()/cron × reinstall/useRealTimers), a
heapStatsleak test for thethis_valuefix, andtest.eachover the four badnowinputs. - Deleted state: the
active: boolfield is removed (replaced bynow.is_some()), and theCURRENT_TIMEstatic /CurrentTimestruct /RwLock/Atomic*imports are gone — verified no remaining readers.
Jarred-Sumner
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that referenced
this pull request
Aug 24, 2026
### Problem
- Under `jest.useFakeTimers({ now })`, `Date.now()` returns the fake
time and `performance.now()` restarts at 0, but `performance.timeOrigin`
stays at the real process start. `performance.timeOrigin +
performance.now()` is then neither the fake time nor the real time: it
is the real process start, so it jumps backwards by the process age at
activation. Tracing code that computes `hrTime = timeOrigin +
performance.now()` records 2026 next to `Date` values of 2000 in one
test.
- The cause is `JSPerformance::finishCreation`
(`src/jsc/bindings/webcore/JSPerformance.cpp:258`): `timeOrigin` was a
read-only own data property, computed once at construction. The fake
clock (`src/runtime/test_runner/timers/FakeTimers.rs`) overrides
`Date.now()` and `performance.now()` but had no way to move it.
### Fix
- `timeOrigin` is now a getter on `Performance.prototype`, as in Node
and browsers. It reads `Bun__readOriginTimerStart` on each access.
`Performance::timeOrigin()` (used by `toJSON()`) reads the same
function.
- The VM gains `overridden_time_origin`, next to
`overridden_performance_now`. The fake clock sets it to
`date_now_offset`, the value that already satisfies `Date.now() ==
date_now_offset + performance.now()`. `useRealTimers()` clears it.
`setSystemTime()` under fake timers moves `Date.now()` but not
`performance.now()`, so it moves the origin too. `setSystemTime()`
without fake timers leaves the real origin alone, as before.
- Correct because `timeOrigin` is by definition the wall-clock time at
which `performance.now()` reads 0. With the fake clock that time is
`date_now_offset`, so `timeOrigin + now() == Date.now()` holds after
`useFakeTimers({ now })`, after `advanceTimersByTime`, and after
`setSystemTime`. `@sinonjs/fake-timers` (Jest) sets `timeOrigin` to the
install epoch too.
- Verified: `test/js/bun/test/fake-timers/fake-timers.test.ts` (two new
tests, the first fails on the released binary). Also
`test/js/web/timers/performance.test.js`,
`test/js/node/perf_hooks/perf_hooks.test.ts`,
`test/js/deno/performance/performance.test.ts`,
`test/js/bun/test/test-timers.test.ts`,
`test/cli/test/isolation.test.ts`, the cron and jsonwebtoken suites.
### Background
- `performance.now()` is a monotonic clock in milliseconds since
`timeOrigin`. `Bun__readOriginTimer`
(`src/jsc/virtual_machine_exports.rs`) returns it in nanoseconds, or the
fake value when `vm.overridden_performance_now` is set.
- `performance.timeOrigin` is the wall-clock time (ms since the Unix
epoch) that `performance.now() == 0` maps to.
`Bun__readOriginTimerStart` returns it from `vm.origin_timestamp`.
- The bun:test fake clock keeps one `Timespec` (`CURRENT_TIME`) for fake
monotonic time and one `date_now_offset` that maps it to the fake
`Date.now()`. `useFakeTimers` resets the monotonic value to 0 and sets
the offset to the requested `now`.
- A `DOMAttribute | CustomAccessor` entry in a prototype hash table is a
getter that JSC type-checks: `this` must be a `Performance` instance, or
JSC throws a `TypeError` before the getter runs.
<details><summary>Notes</summary>
Repro (released bun 1.4.0, `bun test`):
```js
const { test, expect, jest } = require("bun:test");
test("timeOrigin follows the fake clock", () => {
jest.useFakeTimers({ now: new Date("2000-01-01T00:00:00Z") });
console.log(new Date().toISOString(), new Date(performance.timeOrigin + performance.now()).toISOString());
// before: 2000-01-01T00:00:00.000Z 2026-08-22T14:04:35.616Z
// after: 2000-01-01T00:00:00.000Z 2000-01-01T00:00:00.000Z
expect(new Date(performance.timeOrigin + performance.now()).getUTCFullYear()).toBe(2000);
});
```
Observable shape change: `timeOrigin` moves from an own enumerable data
property of `performance` to an accessor on `Performance.prototype`,
which is where Node and browsers put it. `Object.keys(performance)` no
longer lists it. `JSON.stringify(performance)` and
`performance.toJSON()` still include it, and the value is the same.
`performance.now()` still restarts at 0 on `useFakeTimers()`. This
matches `@sinonjs/fake-timers` (the Jest engine) and the existing tests
in `fake-timers.test.ts` assert it. A consequence that this PR does not
change: `performance.mark()` entries recorded before `useFakeTimers()`
stay on the real timeline, so a `measure()` that spans the activation
has a negative duration. Jest stubs `mark()` and `measure()` under fake
timers instead. The alternative is to not reset `performance.now()` at
activation and let the fake monotonic clock continue from the real
reading, which keeps marks comparable across activation. That is a
one-line change in `FakeTimers::activate` plus the two assertions in the
existing tests, if that behaviour is preferred.
`setSystemTime()` under fake timers: `@sinonjs/fake-timers` pins
`timeOrigin` at the install epoch, so there `timeOrigin + now() !=
Date.now()` after `setSystemTime`. This PR moves the origin instead, so
the invariant also holds for the documented `useFakeTimers();
setSystemTime(date)` idiom.
`Bun__FakeTimers__setSystemTime` now takes the global object so it can
reach the VM. `reset_for_isolation` (the `--isolate` file boundary) goes
through `CurrentTime::clear` and so also clears the override.
Related open PR: #38740 moves the fake clock statics to per-VM storage
and touches the same lines in `FakeTimers.rs`. This change is
independent of it and rebases onto it mechanically (set the override
where `date_now_offset` is written).
Formatting: `prettier` and `clang-format` checks pass. `rustfmt` reports
pre-existing diffs in `FakeTimers.rs` (import order, `MIN_TIMESPEC`
layout) that this PR does not touch.
</details>
<!-- robobun:evidence:begin -->
---
**[review]** gate passed · iteration 0 · 7 files touched
<details><summary>fails on main (without fix)</summary>
```console
ASAN without fix: 1 FAILED
$ BUN_DEBUG_QUIET_LOGS=1 bun scripts/build.ts --profile=debug --quiet test "--reporter=junit" "--reporter-outfile=/tmp/mechgate.xml" test/js/bun/test/fake-timers/fake-timers.test.ts
bun test v1.4.1 (4448a2e)
test/js/bun/test/fake-timers/fake-timers.test.ts:
(pass) fake timers [26.51ms]
(pass) advanceTimersToNextTimer > one setTimeout [8.09ms]
(pass) advanceTimersToNextTimer > setInterval [7.11ms]
(pass) advanceTimersToNextTimer > sorted timeouts [10.97ms]
(pass) advanceTimersToNextTimer > alternating intervals [8.47ms]
(pass) advanceTimersByTime > setInterval [6.07ms]
(pass) runOnlyPendingTimers > two setIntervals [7.40ms]
(pass) runAllTimers > two setIntervals [7.75ms]
(pass) getTimerCount > returns correct count of pending timers [6.59ms]
(pass) getTimerCount > throws error if fake timers not active [3.63ms]
(pass) clearAllTimers > clears all pending timers [4.39ms]
(pass) clearAllTimers > throws error if fake timers not active [2.69ms]
(pass) AbortSignal.timeout > pending signals stay alive while the fake heap holds their timer [381.78ms]
(pass) AbortSignal.timeout > useRealTimers() releases the signals whose timers it dropped [401.83ms]
(pass) AbortSignal.tim
... (truncated)
release without fix: 1 FAILED
bun test v1.4.0-canary.1 (4448a2e)
test/js/bun/test/fake-timers/fake-timers.test.ts:
(pass) fake timers [10.42ms]
(pass) advanceTimersToNextTimer > one setTimeout [0.15ms]
(pass) advanceTimersToNextTimer > setInterval [0.09ms]
(pass) advanceTimersToNextTimer > sorted timeouts [0.10ms]
(pass) advanceTimersToNextTimer > alternating intervals [0.10ms]
(pass) advanceTimersByTime > setInterval [0.09ms]
(pass) runOnlyPendingTimers > two setIntervals [0.10ms]
(pass) runAllTimers > two setIntervals [0.06ms]
(pass) getTimerCount > returns correct count of pending timers [0.06ms]
(pass) getTimerCount > throws error if fake timers not active [0.06ms]
(pass) clearAllTimers > clears all pending timers [0.05ms]
(pass) clearAllTimers > throws error if fake timers not active [0.02ms]
(pass) AbortSignal.timeout > pending signals stay alive while the fake heap holds their timer [8.66ms]
(pass) AbortSignal.timeout > useRealTimers() releases the signals whose timers it dropped [6.36ms]
(pass) AbortSignal.timeout > clearAllTimers() releases the signals whose timers it cleared [6.30ms]
(pass) AbortSignal.timeout > a signal the program still holds is left unaborted once its fake timer
... (truncated)
```
</details>
<details><summary>passes on PR (with fix)</summary>
```console
ASAN with fix: all passed
$ BUN_DEBUG_QUIET_LOGS=1 bun scripts/build.ts --profile=debug --quiet test "--reporter=junit" "--reporter-outfile=/tmp/mechgate.xml" test/js/bun/test/fake-timers/fake-timers.test.ts
bun test v1.4.1 (4448a2e)
test/js/bun/test/fake-timers/fake-timers.test.ts:
(pass) fake timers [27.77ms]
(pass) advanceTimersToNextTimer > one setTimeout [7.82ms]
(pass) advanceTimersToNextTimer > setInterval [7.24ms]
(pass) advanceTimersToNextTimer > sorted timeouts [11.21ms]
(pass) advanceTimersToNextTimer > alternating intervals [8.63ms]
(pass) advanceTimersByTime > setInterval [6.18ms]
(pass) runOnlyPendingTimers > two setIntervals [7.32ms]
(pass) runAllTimers > two setIntervals [8.04ms]
(pass) getTimerCount > returns correct count of pending timers [6.75ms]
(pass) getTimerCount > throws error if fake timers not active [3.89ms]
(pass) clearAllTimers > clears all pending timers [5.08ms]
(pass) clearAllTimers > throws error if fake timers not active [2.61ms]
(pass) AbortSignal.timeout > pending signals stay alive while the fake heap holds their timer [389.08ms]
(pass) AbortSignal.timeout > useRealTimers() releases the signals whose timers it dropped [404.88ms]
(pass) AbortSignal.tim
... (truncated)
release with fix: all passed
$ bun scripts/build.ts --profile=release
[configured] bun-profile → bun (stripped) in 694ms (unchanged)
ninja: Entering directory `/workspace/bun/build/release'
[1/10] gen generated_host_exports.rs
generated_host_exports.rs: 92 exports (host=3, lazy=10, generic=79, rust=0); 241 extern-C blocks audited
[2/10] gen cpp.rs (cppbind)
[2/10] cargo bun_runtime → libbun_runtime.a (--target x86_64-unknown-linux-gnu)
nightly-2026-07-20-x86_64-unknown-linux-gnu unchanged - rustc 1.99.0-nightly (9f36de775 2026-07-19)
�[1m�[92m Compiling�[0m bun_install v0.0.0 (/workspace/bun/src/install)
�[1m�[92m Compiling�[0m bun_jsc v0.0.0 (/workspace/bun/src/jsc)
�[1m�[92m Compiling�[0m bun_ast_jsc v0.0.0 (/workspace/bun/src/ast_jsc)
�[1m�[92m Compiling�[0m bun_js_parser_jsc v0.0.0 (/workspace/bun/src/js_parser_jsc)
�[1m�[92m Compiling�[0m bun_http_jsc v0.0.0 (/workspace/bun/src/http_jsc)
�[1m�[92m Compiling�[0m bun_semver_jsc v0.0.0 (/workspace/bun/src/semver_jsc)
�[1m�[92m Compiling�[0m bun_sql_jsc v0.0.0 (/workspace/bun/src/sql_jsc)
�[1m�[92m Compiling�[0m bun_sourcemap_jsc v0.0.0 (/workspace/bun/src/sourcemap_jsc)
�[1m�[92m Compiling�[0m bun_patch_jsc v0.0.0 (/
... (truncated)
```
</details>
<details><summary>diff hotspot</summary>
```
src/jsc/VirtualMachine.rs | 4 +++
src/jsc/bindings/JSMockFunction.cpp | 4 +--
src/jsc/bindings/webcore/JSPerformance.cpp | 19 +++++++++----
src/jsc/bindings/webcore/Performance.cpp | 4 +--
src/jsc/virtual_machine_exports.rs | 4 +++
src/runtime/test_runner/timers/FakeTimers.rs | 12 ++++++--
test/js/bun/test/fake-timers/fake-timers.test.ts | 36 ++++++++++++++++++++++++
7 files changed, 70 insertions(+), 13 deletions(-)
```
</details>
**gate history** · 1 passed · 0 rejected · iteration 0
<details><summary>evidence per changed file</summary>
```
file reads edits tests
src/jsc/VirtualMachine.rs 1 1 0
src/jsc/bindings/JSMockFunction.cpp 1 2 0
src/jsc/bindings/webcore/JSPerformance.cpp 2 4 0
src/jsc/bindings/webcore/Performance.cpp 1 1 0
src/jsc/virtual_machine_exports.rs 1 2 0
src/runtime/test_runner/timers/FakeTimers.rs 1 3 0
test/js/bun/test/fake-timers/fake-timers.test.ts 1 2 0
```
</details>
<!-- robobun:evidence:end -->
alii
pushed a commit
that referenced
this pull request
Aug 25, 2026
### Problem
- `jest.useFakeTimers({ now: NaN })` (or `{ now: new Date(NaN) }`)
leaves `Date.now()` on the real clock but sets `performance.timeOrigin`
to `NaN`. `performance.toJSON()` then fails `ASSERTION FAILED:
!std::isnan(value)` (`JSDOMConvertNumbers.h:349`, `IDLDouble`) in an
assert build. A release build returns `NaN`.
- The cause is `use_fake_timers`
(`src/runtime/test_runner/timers/FakeTimers.rs:362`). It accepts any
number or Date as `now`. `CurrentTime::set` then computes
`date_now_offset = NaN` and stores it as `overridden_time_origin =
Some(NaN)` (line 77). The Date path never sees the override, because
`NaN` is the "no override" sentinel of
`JSGlobalObject::overridenDateNow`. The two clocks disagree.
- Since #40104 (post-1.4.0). 1.4.0 left `timeOrigin` real for the same
input. `advanceTimersByTime(NaN)` has the same class of hole: its range
check is `<` and `>`, both false for `NaN`, so the call passes and
advances by nothing.
### Fix
- `use_fake_timers` throws a `TypeError` for a non-finite `now`: `'now'
must be a finite number or a valid Date`. This covers `NaN`, `Infinity`,
`-Infinity` and an Invalid Date (its timestamp is `NaN`).
- `advance_timers_by_time` rejects `NaN` as out of range. Its two error
messages now name `advanceTimersByTime()` instead of
`advanceTimersToNextTimer()`.
- Correct because user input must not be able to produce the internal
sentinel, and a non-finite clock has no meaning: `Date.now()` cannot
return it and `new Date()` is invalid. `setSystemTime(NaN)` is not
changed. It is documented to reset the Date override, and
`Bun__FakeTimers__setSystemTime` already returns early for `NaN`.
- Verified: `test/js/bun/test/fake-timers/fake-timers.test.ts` (eight
new cases, the `NaN` ones fail on main). Also
`test/js/bun/test/test-timers.test.ts`,
`test/js/web/timers/performance.test.js`,
`test/js/node/perf_hooks/perf_hooks.test.ts`.
### Background
- The bun:test fake clock keeps one fake monotonic `Timespec`
(`CURRENT_TIME`) and one `date_now_offset` that maps it to the fake
`Date.now()`. `useFakeTimers({ now })` resets the monotonic value to 0
and sets the offset to `now`.
- `performance.timeOrigin` is the wall-clock time at which
`performance.now()` reads 0. Under fake timers it is `date_now_offset`
(#40104).
- `JSGlobalObject::overridenDateNow` is a `double`. `jsDateNow()`
returns the real time when it is `NaN`. So a `NaN` offset disables the
Date override but still reaches `overridden_time_origin`.
<details><summary>Notes</summary>
Repro on main (debug build):
```ts
import { test, jest } from "bun:test";
test("nan clock", () => {
jest.useFakeTimers({ now: NaN });
console.log(Date.now()); // real wall clock
console.log(performance.timeOrigin); // NaN
performance.toJSON(); // ASSERTION FAILED: !std::isnan(value)
});
```
`advanceTimersByTime(NaN)` on main (debug build, `useFakeTimers({ now:
1000 })` first): no throw, `Date.now()` stays 1000, `performance.now()`
stays 0, a pending 1 ms timer does not fire. `add_ms_float` floors `NaN`
and the `as i64` cast saturates to 0, so the clock does not move and no
`NaN` reaches `date_now_offset`. The new check makes the mistake
visible. `Infinity` and negatives were already rejected by the range
check.
The `advanceTimersByTime` test asserts on `ms is out of range. It must
be >= 0 and <= 4294967295` and not on the function name, so the `-1`,
`Infinity` and `2 ** 32` cases pass on main and the `NaN` case is the
one that fails there.
The other option for `now` was to treat `NaN` as "no Date override",
which is what 1.4.0 did by accident. That state is odd: timers and
`performance.now()` are fake, `Date.now()` is real, and `timeOrigin +
performance.now()` is neither. Nobody asks for it on purpose, so the
error is the more useful response.
`Infinity` was accepted as the clock on 1.4.0 too (`Date.now() ===
Infinity`). The `is_finite()` check rejects it as well.
Jest with `@sinonjs/fake-timers` maps a `NaN` `now` to epoch 0 (a falsy
check in `getEpoch`) and an Invalid Date to a `NaN` clock. Neither is a
contract to match.
Related open PR: #38740 moves the fake clock statics to per-VM storage
and touches `FakeTimers.rs`. This change is in `use_fake_timers` and
`advance_timers_by_time` only and rebases onto it mechanically.
</details>
This was referenced Aug 26, 2026
This was referenced Sep 8, 2026
Jarred-Sumner
pushed a commit
that referenced
this pull request
Sep 15, 2026
…llback 1ms later (#42728) ### Problem - Under `jest.useFakeTimers()`, `advanceTimersByTime()` and `runOnlyPendingTimers()` never return when a timer callback arms the next timer with no delay: an `AbortSignal.timeout(0)` armed again by its own `abort` listener, or a `while (!done) await Bun.sleep(0)` loop. Bun spins inside one host call, so no test timeout fires. Fuzz-found, no user report. - `FakeTimers::execute_until` (`src/runtime/test_runner/timers/FakeTimers.rs:274`) fires every timer due at or before its target. Such a timer lands on the current fake instant, so it is due again. ### Fix - While a fake timer's callback runs, a timer armed with no delay gets 1ms (`FakeTimers::min_delay_ms`). Both arm sites that accept 0 use it: `AbortSignal::Timeout::init` (new `RuntimeHooks` slot) and `TimerObjectInternals::reschedule` (`Bun.sleep`). - `@sinonjs/fake-timers` has this rule (`addTimer`: `delay || (duringTick ? 1 : 0)`). Each re-armed timer is 1ms later, so the drain ends. Real timers and interval re-arms do not change. - Verified: `test/js/bun/test/fake-timers/fake-timers.test.ts` (11 new cases, 8 fail without the fix). Also the rest of that directory, `test-timers`, `sleep`, cron, `web/abort`. - Self-reviewed: 15 concerns raised, 9 addressed, 5 needed no change, 1 rejected. ### Background - The `jest` timer controls pop due timers from a fake heap and run each through `FakeTimers::fire`, which first sets the fake clock. - `setTimeout(fn, 0)` is always 1ms. Only `AbortSignal.timeout(0)` and `Bun.sleep(0)` arm with no delay. - `RuntimeHooks` is the function table through which `bun_jsc` (`AbortSignal`) calls up into `bun_runtime` (the timer heap). - With no event loop task on the stack (the first tests of a file), `fire` also drains the callback's microtasks. The `Bun.sleep(0)` loop re-arms there. <details><summary>Notes</summary> Repro (the bound keeps it from hanging): ```js const { jest } = Bun.jest(); jest.useFakeTimers(); let fires = 0; const arm = () => AbortSignal.timeout(0).addEventListener("abort", () => { if (++fires < 20000) arm(); }); arm(); jest.advanceTimersByTime(1); // same with jest.runOnlyPendingTimers() console.log(fires, performance.now()); ``` | | 1.4.3 | this PR | lolex 5.1.2, `setTimeout(fn, 0)` re-armed | |---|---|---|---| | `advanceTimersByTime(1)` / `tick(1)` | 20000 fires, all at 0 | 2 fires, at 0 and 1 | 2 fires, at 0 and 1 | | `runOnlyPendingTimers()` / `runToLast()` | 20000 fires, all at 0 | 1 fire, at 0 | 1 fire, at 0 | | `advanceTimersToNextTimer()` twice / `next()` twice | fires at 0 and 0 | fires at 0 and 1 | fires at 0 and 1 | The `Bun.sleep(0)` loop, as the first test of a file: `setTimeout(() => (done = true), 3)`, then `(async () => { while (!done) await Bun.sleep(0); })()`, then `advanceTimersByTime(5)`. 1.4.3 polls forever at instant 0. This PR polls at 0, 0, 1, 2 and returns with the clock at 5. After a test that awaited a real timer, the controls run inside an event loop task and do not drain microtasks between timers. There the loop never spun, and it does not change. Behavior changes beyond the hang. Each equals what `setTimeout(fn, 0)` already does in Bun and in Jest: - An `AbortSignal.timeout(0)` that a fake timer callback arms fires 1ms after that callback. Before, it fired at the same fake instant, inside the same `advanceTimersByTime()` call. - A `Bun.sleep(0)` (any value below 1) that a fake timer callback calls resolves 1ms after that callback. - `advanceTimersToNextTimer()` moves the clock to the re-armed timer, 1ms later. Before, the clock stayed. The rule is on the requested delay, and not on the deadline. A first version compared the deadline with the fake clock in `All::insert`. That also moved a `setInterval(fn, 10)` whose callback calls `advanceTimersByTime(10)` (its next deadline equals the clock) from 10, 20, 30 to 10, 21, 31, and an `_idleStart` write that lands on the clock. Neither is a zero delay. Two of the new tests hold the interval case. `firing` is a depth counter and not a flag. A listener can call a nested timer control, which fires another timer and returns into the listener. A flag is clear from then on, and a zero-delay timer that the listener arms afterwards spins the outer drain again. One of the new tests covers this. The count spans the whole `EventLoopTimer::fire` call, which includes the microtask drain on return. Timer control calls that still do not return, and where they stand: - `runAllTimers()` with a timer that always re-arms (`setInterval`, `Bun.cron`, the repro above). Unbounded by design, in Jest too. Jest stops at `timerLimit`. #34325 added that cap and is closed. This PR does not change `runAllTimers()`. `tick()` has no loop limit in Jest or sinon, so a count cap on `execute_until` is not the right shape. - A callback that writes `_idleStart` so that a timer is due at the current instant, in a cycle. That is an explicit absolute deadline. Not changed. - The test timeout cannot interrupt any synchronous spin: #30598, #21277. That is the rejected review concern. It is a backstop for all of these, and a separate change. Related PRs. None of them is a prerequisite. Each pair needs a textual merge only: - #42045 (never move the fake clock backwards) changes `fire()` and `advance_timers_by_time`. Its tests arm no zero-delay timer, so this change cannot move their values. - #38740 (per-VM fake clock) moves the clock into `FakeTimers`. It also covers a callback that installs the fake clock again. - #41571 adds an `execute_until(now)` step to `advanceTimersToNextTimer()`. Without this rule that step has the same hang. - #40187 (timer: remove unsafe) rewrites the timer module. `node:test` `mock.timers` (#32631) is a separate implementation in `src/js/internal/test_runner/mock_timers.ts`. It replaces `AbortSignal.timeout` with its own timers and has its own `tick()`. This PR does not touch it. Suites run on the debug ASAN build: `test/js/bun/test/fake-timers/` (the sinon port gives the same pass, fail and todo sets with `--todo` as 1.4.3), `test/js/bun/test/test-timers.test.ts`, `test/js/bun/util/sleep.test.ts`, `test/js/bun/cron/in-process-cron.test.ts`, `test/js/bun/cron/cron-local-time.test.ts`, `test/regression/issue/26284.test.ts`, `test/regression/issue/25869.test.ts`, `test/js/third_party/jsonwebtoken/`, `test/js/web/abort/`, the fake timers case of `test/cli/test/isolation.test.ts`, `test/internal/source-lints/`, and `cargo clippy -p bun_jsc -p bun_runtime`. `test/js/web/timers/setTimeout.test.js`, `setInterval.test.js` and `timer-gc-roots.test.ts` have 5 failures on my machine under the debug ASAN build (RSS thresholds and one 5s timeout). The same 5 fail with `src/` at `main`. </details> <!-- robobun:evidence:begin --> --- **[human-review]** gate passed · iteration 0 · 6 files touched <details><summary>fails on main (without fix)</summary> ```console ASAN without fix: 8 FAILED $ BUN_DEBUG_QUIET_LOGS=1 bun scripts/build.ts --profile=debug --quiet test "--reporter=junit" "--reporter-outfile=/tmp/pr_gate.xml" test/js/bun/test/fake-timers/fake-timers.test.ts bun test v1.4.3 (09bb546) test/js/bun/test/fake-timers/fake-timers.test.ts: (pass) fake timers [25.32ms] (pass) advanceTimersToNextTimer > one setTimeout [9.05ms] (pass) advanceTimersToNextTimer > setInterval [8.07ms] (pass) advanceTimersToNextTimer > sorted timeouts [13.08ms] (pass) advanceTimersToNextTimer > alternating intervals [9.95ms] (pass) advanceTimersByTime > setInterval [6.35ms] (pass) advanceTimersByTime > advanceTimersByTime(NaN) throws and does not move the clock [5.91ms] (pass) advanceTimersByTime > advanceTimersByTime(-1) throws and does not move the clock [1.24ms] (pass) advanceTimersByTime > advanceTimersByTime(Infinity) throws and does not move the clock [0.91ms] (pass) advanceTimersByTime > advanceTimersByTime(4294967296) throws and does not move the clock [1.47ms] (pass) runOnlyPendingTimers > two setIntervals [7.85ms] (pass) runAllTimers > two setIntervals [9.60ms] (pass) getTimerCount > returns correct count of pending timers [8.65ms] (pass) getTimerCount > throw ... (truncated) release without fix: 8 FAILED bun test v1.4.3-canary.1 (09bb546) test/js/bun/test/fake-timers/fake-timers.test.ts: (pass) fake timers [10.41ms] (pass) advanceTimersToNextTimer > one setTimeout [0.14ms] (pass) advanceTimersToNextTimer > setInterval [0.09ms] (pass) advanceTimersToNextTimer > sorted timeouts [0.11ms] (pass) advanceTimersToNextTimer > alternating intervals [0.08ms] (pass) advanceTimersByTime > setInterval [0.07ms] (pass) advanceTimersByTime > advanceTimersByTime(NaN) throws and does not move the clock [0.10ms] (pass) advanceTimersByTime > advanceTimersByTime(-1) throws and does not move the clock (pass) advanceTimersByTime > advanceTimersByTime(Infinity) throws and does not move the clock (pass) advanceTimersByTime > advanceTimersByTime(4294967296) throws and does not move the clock (pass) runOnlyPendingTimers > two setIntervals [0.13ms] (pass) runAllTimers > two setIntervals [0.07ms] (pass) getTimerCount > returns correct count of pending timers [0.06ms] (pass) getTimerCount > throws error if fake timers not active [0.02ms] (pass) clearAllTimers > clears all pending timers [0.05ms] (pass) clearAllTimers > throws error if fake timers not active [0.02ms] (pass) AbortSignal.timeout ... (truncated) ``` </details> <details><summary>passes on PR (with fix)</summary> ```console ASAN with fix: all passed $ BUN_DEBUG_QUIET_LOGS=1 bun scripts/build.ts --profile=debug --quiet test "--reporter=junit" "--reporter-outfile=/tmp/pr_gate.xml" test/js/bun/test/fake-timers/fake-timers.test.ts bun test v1.4.3 (09bb546) test/js/bun/test/fake-timers/fake-timers.test.ts: (pass) fake timers [26.39ms] (pass) advanceTimersToNextTimer > one setTimeout [9.05ms] (pass) advanceTimersToNextTimer > setInterval [8.23ms] (pass) advanceTimersToNextTimer > sorted timeouts [13.11ms] (pass) advanceTimersToNextTimer > alternating intervals [10.00ms] (pass) advanceTimersByTime > setInterval [6.67ms] (pass) advanceTimersByTime > advanceTimersByTime(NaN) throws and does not move the clock [6.56ms] (pass) advanceTimersByTime > advanceTimersByTime(-1) throws and does not move the clock [1.29ms] (pass) advanceTimersByTime > advanceTimersByTime(Infinity) throws and does not move the clock [0.91ms] (pass) advanceTimersByTime > advanceTimersByTime(4294967296) throws and does not move the clock [1.56ms] (pass) runOnlyPendingTimers > two setIntervals [8.18ms] (pass) runAllTimers > two setIntervals [9.79ms] (pass) getTimerCount > returns correct count of pending timers [8.87ms] (pass) getTimerCount > thro ... (truncated) release with fix: all passed $ bun scripts/build.ts --profile=release [configured] bun-profile → bun (stripped) target linux-x64-gnu build type Release build dir ./build/release revision b23c2c8 features baseline 23 deps, 131 codegen, 1176 objects in 692ms ninja: Entering directory `/workspace/bun/build/release' [1/1248] install /workspace/bun bun install v1.4.3-canary.1 (09bb546) Checked 22 installs across 61 packages (no changes) [14.00ms] [2/1248] install /workspace/bun/packages/bun-error bun install v1.4.3-canary.1 (09bb546) Checked 1 install across 2 packages (no changes) [1.00ms] [3/1248] gen ErrorCode+*.h [4/1248] gen bindgenv2 [5/1248] install /workspace/bun/src/node-fallbacks bun install v1.4.3-canary.1 (09bb546) Checked 111 installs across 104 packages (no changes) [4.00ms] [6/1248] fetch zlib [zlib] up to date [7/1248] fetch tinycc [tinycc] up to date [8/1247] fetch libjpeg-turbo [libjpeg-turbo] up to date [9/1220] gen node-fallbacks/react-refresh.js Bundled 1 module in 7ms react-refresh.js 4.81 KB (entry point) [10/1220] gen .bind.ts → GeneratedBindings.cpp [11/1220] gen bake.{client,server,error}.js -> bake.client.js, bake.server ... (truncated) ``` </details> <details><summary>diff hotspot</summary> ``` src/jsc/AbortSignal.rs | 1 + src/jsc/VirtualMachine.rs | 9 ++ src/runtime/jsc_hooks.rs | 11 ++ src/runtime/test_runner/timers/FakeTimers.rs | 13 ++ src/runtime/timer/timer_object_internals.rs | 5 +- test/js/bun/test/fake-timers/fake-timers.test.ts | 189 ++++++++++++++++++++++- 6 files changed, 226 insertions(+), 2 deletions(-) ``` </details> **gate history** · 1 passed · 0 rejected · iteration 0 <details><summary>evidence per changed file</summary> ``` file reads edits tests src/jsc/AbortSignal.rs 2 2 24 src/jsc/VirtualMachine.rs 4 5 23 src/runtime/jsc_hooks.rs 2 3 23 src/runtime/test_runner/timers/FakeTimers.rs 3 7 22 src/runtime/timer/timer_object_internals.rs 3 1 22 test/js/bun/test/fake-timers/fake-timers.test.ts 5 5 22 ``` </details> <!-- robobun:evidence:end --> --------- Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>
usrbinkat
pushed a commit
to usrbinkat/bun
that referenced
this pull request
Sep 15, 2026
…llback 1ms later (oven-sh#42728) ### Problem - Under `jest.useFakeTimers()`, `advanceTimersByTime()` and `runOnlyPendingTimers()` never return when a timer callback arms the next timer with no delay: an `AbortSignal.timeout(0)` armed again by its own `abort` listener, or a `while (!done) await Bun.sleep(0)` loop. Bun spins inside one host call, so no test timeout fires. Fuzz-found, no user report. - `FakeTimers::execute_until` (`src/runtime/test_runner/timers/FakeTimers.rs:274`) fires every timer due at or before its target. Such a timer lands on the current fake instant, so it is due again. ### Fix - While a fake timer's callback runs, a timer armed with no delay gets 1ms (`FakeTimers::min_delay_ms`). Both arm sites that accept 0 use it: `AbortSignal::Timeout::init` (new `RuntimeHooks` slot) and `TimerObjectInternals::reschedule` (`Bun.sleep`). - `@sinonjs/fake-timers` has this rule (`addTimer`: `delay || (duringTick ? 1 : 0)`). Each re-armed timer is 1ms later, so the drain ends. Real timers and interval re-arms do not change. - Verified: `test/js/bun/test/fake-timers/fake-timers.test.ts` (11 new cases, 8 fail without the fix). Also the rest of that directory, `test-timers`, `sleep`, cron, `web/abort`. - Self-reviewed: 15 concerns raised, 9 addressed, 5 needed no change, 1 rejected. ### Background - The `jest` timer controls pop due timers from a fake heap and run each through `FakeTimers::fire`, which first sets the fake clock. - `setTimeout(fn, 0)` is always 1ms. Only `AbortSignal.timeout(0)` and `Bun.sleep(0)` arm with no delay. - `RuntimeHooks` is the function table through which `bun_jsc` (`AbortSignal`) calls up into `bun_runtime` (the timer heap). - With no event loop task on the stack (the first tests of a file), `fire` also drains the callback's microtasks. The `Bun.sleep(0)` loop re-arms there. <details><summary>Notes</summary> Repro (the bound keeps it from hanging): ```js const { jest } = Bun.jest(); jest.useFakeTimers(); let fires = 0; const arm = () => AbortSignal.timeout(0).addEventListener("abort", () => { if (++fires < 20000) arm(); }); arm(); jest.advanceTimersByTime(1); // same with jest.runOnlyPendingTimers() console.log(fires, performance.now()); ``` | | 1.4.3 | this PR | lolex 5.1.2, `setTimeout(fn, 0)` re-armed | |---|---|---|---| | `advanceTimersByTime(1)` / `tick(1)` | 20000 fires, all at 0 | 2 fires, at 0 and 1 | 2 fires, at 0 and 1 | | `runOnlyPendingTimers()` / `runToLast()` | 20000 fires, all at 0 | 1 fire, at 0 | 1 fire, at 0 | | `advanceTimersToNextTimer()` twice / `next()` twice | fires at 0 and 0 | fires at 0 and 1 | fires at 0 and 1 | The `Bun.sleep(0)` loop, as the first test of a file: `setTimeout(() => (done = true), 3)`, then `(async () => { while (!done) await Bun.sleep(0); })()`, then `advanceTimersByTime(5)`. 1.4.3 polls forever at instant 0. This PR polls at 0, 0, 1, 2 and returns with the clock at 5. After a test that awaited a real timer, the controls run inside an event loop task and do not drain microtasks between timers. There the loop never spun, and it does not change. Behavior changes beyond the hang. Each equals what `setTimeout(fn, 0)` already does in Bun and in Jest: - An `AbortSignal.timeout(0)` that a fake timer callback arms fires 1ms after that callback. Before, it fired at the same fake instant, inside the same `advanceTimersByTime()` call. - A `Bun.sleep(0)` (any value below 1) that a fake timer callback calls resolves 1ms after that callback. - `advanceTimersToNextTimer()` moves the clock to the re-armed timer, 1ms later. Before, the clock stayed. The rule is on the requested delay, and not on the deadline. A first version compared the deadline with the fake clock in `All::insert`. That also moved a `setInterval(fn, 10)` whose callback calls `advanceTimersByTime(10)` (its next deadline equals the clock) from 10, 20, 30 to 10, 21, 31, and an `_idleStart` write that lands on the clock. Neither is a zero delay. Two of the new tests hold the interval case. `firing` is a depth counter and not a flag. A listener can call a nested timer control, which fires another timer and returns into the listener. A flag is clear from then on, and a zero-delay timer that the listener arms afterwards spins the outer drain again. One of the new tests covers this. The count spans the whole `EventLoopTimer::fire` call, which includes the microtask drain on return. Timer control calls that still do not return, and where they stand: - `runAllTimers()` with a timer that always re-arms (`setInterval`, `Bun.cron`, the repro above). Unbounded by design, in Jest too. Jest stops at `timerLimit`. oven-sh#34325 added that cap and is closed. This PR does not change `runAllTimers()`. `tick()` has no loop limit in Jest or sinon, so a count cap on `execute_until` is not the right shape. - A callback that writes `_idleStart` so that a timer is due at the current instant, in a cycle. That is an explicit absolute deadline. Not changed. - The test timeout cannot interrupt any synchronous spin: oven-sh#30598, oven-sh#21277. That is the rejected review concern. It is a backstop for all of these, and a separate change. Related PRs. None of them is a prerequisite. Each pair needs a textual merge only: - oven-sh#42045 (never move the fake clock backwards) changes `fire()` and `advance_timers_by_time`. Its tests arm no zero-delay timer, so this change cannot move their values. - oven-sh#38740 (per-VM fake clock) moves the clock into `FakeTimers`. It also covers a callback that installs the fake clock again. - oven-sh#41571 adds an `execute_until(now)` step to `advanceTimersToNextTimer()`. Without this rule that step has the same hang. - oven-sh#40187 (timer: remove unsafe) rewrites the timer module. `node:test` `mock.timers` (oven-sh#32631) is a separate implementation in `src/js/internal/test_runner/mock_timers.ts`. It replaces `AbortSignal.timeout` with its own timers and has its own `tick()`. This PR does not touch it. Suites run on the debug ASAN build: `test/js/bun/test/fake-timers/` (the sinon port gives the same pass, fail and todo sets with `--todo` as 1.4.3), `test/js/bun/test/test-timers.test.ts`, `test/js/bun/util/sleep.test.ts`, `test/js/bun/cron/in-process-cron.test.ts`, `test/js/bun/cron/cron-local-time.test.ts`, `test/regression/issue/26284.test.ts`, `test/regression/issue/25869.test.ts`, `test/js/third_party/jsonwebtoken/`, `test/js/web/abort/`, the fake timers case of `test/cli/test/isolation.test.ts`, `test/internal/source-lints/`, and `cargo clippy -p bun_jsc -p bun_runtime`. `test/js/web/timers/setTimeout.test.js`, `setInterval.test.js` and `timer-gc-roots.test.ts` have 5 failures on my machine under the debug ASAN build (RSS thresholds and one 5s timeout). The same 5 fail with `src/` at `main`. </details> <!-- robobun:evidence:begin --> --- **[human-review]** gate passed · iteration 0 · 6 files touched <details><summary>fails on main (without fix)</summary> ```console ASAN without fix: 8 FAILED $ BUN_DEBUG_QUIET_LOGS=1 bun scripts/build.ts --profile=debug --quiet test "--reporter=junit" "--reporter-outfile=/tmp/pr_gate.xml" test/js/bun/test/fake-timers/fake-timers.test.ts bun test v1.4.3 (09bb546) test/js/bun/test/fake-timers/fake-timers.test.ts: (pass) fake timers [25.32ms] (pass) advanceTimersToNextTimer > one setTimeout [9.05ms] (pass) advanceTimersToNextTimer > setInterval [8.07ms] (pass) advanceTimersToNextTimer > sorted timeouts [13.08ms] (pass) advanceTimersToNextTimer > alternating intervals [9.95ms] (pass) advanceTimersByTime > setInterval [6.35ms] (pass) advanceTimersByTime > advanceTimersByTime(NaN) throws and does not move the clock [5.91ms] (pass) advanceTimersByTime > advanceTimersByTime(-1) throws and does not move the clock [1.24ms] (pass) advanceTimersByTime > advanceTimersByTime(Infinity) throws and does not move the clock [0.91ms] (pass) advanceTimersByTime > advanceTimersByTime(4294967296) throws and does not move the clock [1.47ms] (pass) runOnlyPendingTimers > two setIntervals [7.85ms] (pass) runAllTimers > two setIntervals [9.60ms] (pass) getTimerCount > returns correct count of pending timers [8.65ms] (pass) getTimerCount > throw ... (truncated) release without fix: 8 FAILED bun test v1.4.3-canary.1 (09bb546) test/js/bun/test/fake-timers/fake-timers.test.ts: (pass) fake timers [10.41ms] (pass) advanceTimersToNextTimer > one setTimeout [0.14ms] (pass) advanceTimersToNextTimer > setInterval [0.09ms] (pass) advanceTimersToNextTimer > sorted timeouts [0.11ms] (pass) advanceTimersToNextTimer > alternating intervals [0.08ms] (pass) advanceTimersByTime > setInterval [0.07ms] (pass) advanceTimersByTime > advanceTimersByTime(NaN) throws and does not move the clock [0.10ms] (pass) advanceTimersByTime > advanceTimersByTime(-1) throws and does not move the clock (pass) advanceTimersByTime > advanceTimersByTime(Infinity) throws and does not move the clock (pass) advanceTimersByTime > advanceTimersByTime(4294967296) throws and does not move the clock (pass) runOnlyPendingTimers > two setIntervals [0.13ms] (pass) runAllTimers > two setIntervals [0.07ms] (pass) getTimerCount > returns correct count of pending timers [0.06ms] (pass) getTimerCount > throws error if fake timers not active [0.02ms] (pass) clearAllTimers > clears all pending timers [0.05ms] (pass) clearAllTimers > throws error if fake timers not active [0.02ms] (pass) AbortSignal.timeout ... (truncated) ``` </details> <details><summary>passes on PR (with fix)</summary> ```console ASAN with fix: all passed $ BUN_DEBUG_QUIET_LOGS=1 bun scripts/build.ts --profile=debug --quiet test "--reporter=junit" "--reporter-outfile=/tmp/pr_gate.xml" test/js/bun/test/fake-timers/fake-timers.test.ts bun test v1.4.3 (09bb546) test/js/bun/test/fake-timers/fake-timers.test.ts: (pass) fake timers [26.39ms] (pass) advanceTimersToNextTimer > one setTimeout [9.05ms] (pass) advanceTimersToNextTimer > setInterval [8.23ms] (pass) advanceTimersToNextTimer > sorted timeouts [13.11ms] (pass) advanceTimersToNextTimer > alternating intervals [10.00ms] (pass) advanceTimersByTime > setInterval [6.67ms] (pass) advanceTimersByTime > advanceTimersByTime(NaN) throws and does not move the clock [6.56ms] (pass) advanceTimersByTime > advanceTimersByTime(-1) throws and does not move the clock [1.29ms] (pass) advanceTimersByTime > advanceTimersByTime(Infinity) throws and does not move the clock [0.91ms] (pass) advanceTimersByTime > advanceTimersByTime(4294967296) throws and does not move the clock [1.56ms] (pass) runOnlyPendingTimers > two setIntervals [8.18ms] (pass) runAllTimers > two setIntervals [9.79ms] (pass) getTimerCount > returns correct count of pending timers [8.87ms] (pass) getTimerCount > thro ... (truncated) release with fix: all passed $ bun scripts/build.ts --profile=release [configured] bun-profile → bun (stripped) target linux-x64-gnu build type Release build dir ./build/release revision b23c2c8 features baseline 23 deps, 131 codegen, 1176 objects in 692ms ninja: Entering directory `/workspace/bun/build/release' [1/1248] install /workspace/bun bun install v1.4.3-canary.1 (09bb546) Checked 22 installs across 61 packages (no changes) [14.00ms] [2/1248] install /workspace/bun/packages/bun-error bun install v1.4.3-canary.1 (09bb546) Checked 1 install across 2 packages (no changes) [1.00ms] [3/1248] gen ErrorCode+*.h [4/1248] gen bindgenv2 [5/1248] install /workspace/bun/src/node-fallbacks bun install v1.4.3-canary.1 (09bb546) Checked 111 installs across 104 packages (no changes) [4.00ms] [6/1248] fetch zlib [zlib] up to date [7/1248] fetch tinycc [tinycc] up to date [8/1247] fetch libjpeg-turbo [libjpeg-turbo] up to date [9/1220] gen node-fallbacks/react-refresh.js Bundled 1 module in 7ms react-refresh.js 4.81 KB (entry point) [10/1220] gen .bind.ts → GeneratedBindings.cpp [11/1220] gen bake.{client,server,error}.js -> bake.client.js, bake.server ... (truncated) ``` </details> <details><summary>diff hotspot</summary> ``` src/jsc/AbortSignal.rs | 1 + src/jsc/VirtualMachine.rs | 9 ++ src/runtime/jsc_hooks.rs | 11 ++ src/runtime/test_runner/timers/FakeTimers.rs | 13 ++ src/runtime/timer/timer_object_internals.rs | 5 +- test/js/bun/test/fake-timers/fake-timers.test.ts | 189 ++++++++++++++++++++++- 6 files changed, 226 insertions(+), 2 deletions(-) ``` </details> **gate history** · 1 passed · 0 rejected · iteration 0 <details><summary>evidence per changed file</summary> ``` file reads edits tests src/jsc/AbortSignal.rs 2 2 24 src/jsc/VirtualMachine.rs 4 5 23 src/runtime/jsc_hooks.rs 2 3 23 src/runtime/test_runner/timers/FakeTimers.rs 3 7 22 src/runtime/timer/timer_object_internals.rs 3 1 22 test/js/bun/test/fake-timers/fake-timers.test.ts 5 5 22 ``` </details> <!-- robobun:evidence:end --> --------- Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>
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What does this PR do?
jest.useFakeTimers()kept its clock in process-global statics (CURRENT_TIMEinFakeTimers.rsandbun_core::mock_time) while the fake timer heap it drives is per-VM. Two workers — or a worker and the main thread — that both used fake timers therefore shared one clock:FakeTimers::firepanics (assertion failed: now.eql(&prev.unwrap()) || now.greater(&prev.unwrap()), reached fromrunOnlyPendingTimers);setSystemTime()/advanceTimersByTime()silently moves the other VM'sDate.now();setTimeouts against the fake epoch, so they fire immediately.The clock (
now,date_now_offset) now lives on the per-VMFakeTimersnext to the heap it drives, andbun_core::mock_timeis thread-local soTimespec::now(AllowMockedTime)reads the calling VM's clock.Date.now()/performance.now()overrides were already per-global. Single-VM behaviour is unchanged.Two related fixes found while auditing the readers of the fake clock:
advanceTimersByTimere-pinned the clock to its target unconditionally after draining, so a fired callback that calleduseRealTimers()leftDate.now()/performance.now()/ the timer clock fake whileisFakeTimers()reported false. It now only advances if fake timers are still active (which also lets the redundantactiveflag go — it was alwaysnow.is_some()).useFakeTimers()now installs a fresh clock, as in Jest and Vitest: calling it while fake timers are already active drops the timers pending on the old clock instead of keeping them scheduled against a reset epoch. Each installation carries a generation, soadvanceTimersByTime/runOnlyPendingTimers/runAllTimersstop draining if a callback they fired installed a new clock.setInterval,Bun.cron()) is out of the heap while its callback runs, souseRealTimers()/useFakeTimers()called from that callback couldn't drop it and it was rescheduled afterwards at a deadline from the old fake timeline — escaping onto the real clock (a cron job also kept the process alive), or surviving into the new fake clock. It is now retired/stopped with the rest of its clock's timers.setIntervalretired from inside its own callback withoutclearInterval()(the clock swap above, or the pre-existing_repeat = null/_idleTimeout = -1path) kept its JS wrapper pinned, leaking the wrapper and the nativeTimeoutObject; the retire path now drops the pin.useFakeTimers({ now })rejects NaN / ±Infinity / invalid Date instead of installing a clock with a NaNDate.now()offset.How did you verify your code works?
New tests in
test/js/bun/test/fake-timers/fake-timers.test.ts: two eval workers run 400 rounds ofuseFakeTimers/setSystemTime/runOnlyPendingTimerswith different clocks and report any round whereDate.now()isn't where their own clock puts it; and a worker exits with fake timers active, after which a main-threadsetTimeout(20)must not fire early; anduseRealTimers()from inside a callback fired byadvanceTimersByTimesticks;useFakeTimers()from a fired callback / while already active installs a fresh clock.Both fail before this change (
bun bd test: panic infire;USE_SYSTEM_BUN=1: hundreds of mismatched rounds andfiredEarly: true) and pass after; the rest of the file andtest-timers.test.tsstill pass. Also diffed the output of a single-VMuseFakeTimers({now})/advanceTimersByTime/setSystemTime/runAllTimers/useRealTimersscript between the debug build and the current release — identical.