[robobun]

Fixes #44221

Problem

• process.hrtime() and process.hrtime.bigint() in a Worker count from the worker's start. A reading in a worker is as far behind the main thread as the main thread ran before it spawned the worker (about 1000 ms in the issue's repro). Node reads one clock (uv_hrtime) on every thread.
• The cause: VirtualMachine::init (src/jsc/VirtualMachine.rs:3191) sets origin_timer = Instant::now() for every VM, main and worker. Bun__readOriginTimer (src/jsc/virtual_machine_exports.rs:38) reads that per-VM field.
• process.uptime(), Bun.nanoseconds(), performance.now() and performance.timeOrigin read the same fields, so they differ across threads too. Node shares all of them (a worker's performance.timeOrigin equals the main thread's).

Fix

• Replace the per-VM origin_timer and origin_timestamp fields with one process-wide ProcessOrigin in a OnceLock. The first VirtualMachine::init call seeds it, on the main thread, so process.uptime() keeps its start point.
• read_origin_timer and read_origin_timer_start read the shared origin. The per-VM fake-timer overrides stay and are checked first, so bun:test fake timers still move process.hrtime() and performance.now().
• Correct because every reader goes through these two functions, so one origin fixes hrtime, uptime, Bun.nanoseconds, performance.now and timeOrigin together, as in node.
• Verified: test/js/node/process/process.test.js (new test, fails on 1.4.3). Also test/js/bun/test/fake-timers/, test/js/web/timers/performance.test.js, test/js/node/perf_hooks/, node's test-process-hrtime*.js.

Background

• A VirtualMachine is bun's per-thread runtime state. The main thread has one, and each Worker creates its own on its thread through the same init.
• Bun__readOriginTimer returns nanoseconds since the origin. Bun__readOriginTimerStart returns the origin as wall-clock milliseconds, for performance.timeOrigin.
• Considered reading CLOCK_MONOTONIC directly in Process_functionHRTime: that breaks the fake-timer override for hrtime and leaves uptime, Bun.nanoseconds and worker performance.now unchanged. Considered copying a shared origin into each VM's fields (the shape in node:worker_threads: per-thread --use-system-ca, real eventLoopUtilization, --cpu-prof in workers, node's online timing, error.code / stack-getter / timeOrigin fixes, async_hooks WORKER resource, worker_threads dc channel (+10 upstream tests) #34424): that keeps a second place that a future init path can re-seed. One static that every reader uses removes that.
• node:worker_threads: per-thread --use-system-ca, real eventLoopUtilization, --cpu-prof in workers, node's online timing, error.code / stack-getter / timeOrigin fixes, async_hooks WORKER resource, worker_threads dc channel (+10 upstream tests) #34424 carries the same idea as part of a larger change. This PR is the standalone fix. Self-reviewed: 3 concerns raised, 3 addressed (all were requests for PR body text).

Downsides

• A worker's performance.now(), Bun.nanoseconds() and process.uptime() now start at the process's elapsed time instead of near 0, and a worker's performance.timeOrigin equals the main thread's. This matches node. Code that treated a worker's performance.now() as "time since the worker started" sees larger values.
• Per call, OnceLock::get_or_init adds one atomic load (Acquire) and one branch in place of one field load. Counted from the code. perf and valgrind are not installed in the build container, so no instruction count.
• Per VM, 24 bytes removed (Instant plus u64).

Notes

Node check (v26.3.0), main thread sleeps 500 ms then spawns a worker that posts its readings:

node:  main now 1327.76  worker now 1326.66
       main origin 1790684962459.299  worker origin 1790684962459.299
       main uptime 1.328  worker uptime 1.326
bun 1.4.3:
       main now 571.46   worker now 46.26
       main origin 1790684963853.103  worker origin 1790684964377.878
       main uptime 0.572  worker uptime 0.046

Node's test/parallel/test-perf-hooks-worker-timeorigin.js asserts strictEqual(workerTimeOrigin, performance.timeOrigin).

The issue's repro with this branch: main - worker (ms): 20.5 (debug build, the worker's message hop), against about 1013 ms on 1.4.3.

Suites run with the debug build: test/js/node/process/process.test.js (the only failure is the pre-existing process test, which needs $USER in the environment and fails the same way on 1.4.3 in this container), test/js/bun/test/fake-timers/ (all files), test/js/web/timers/performance.test.js, test/js/node/perf_hooks/perf_hooks.test.ts, test/js/node/test/parallel/test-process-hrtime.js, test/js/node/test/parallel/test-process-hrtime-bigint.js.

No test under test/js/web/workers or test/js/node/worker_threads depends on a worker's performance.now() starting near zero.

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no test proof · iteration 2 · platform-specific test(s) that do not run on this machine, deferring to CI, which covers all platforms: test/js/node/process/process.test.js

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Walkthrough

Virtual machines now use a process-wide clock origin. Clock exports read from that shared origin. A new test compares clock readings between the main thread and a worker.

Changes

Process-wide clock origin

Layer / File(s)	Summary
Shared origin initialization src/jsc/VirtualMachine.rs	Removes per-VM origin fields. Adds a process-wide origin for monotonic and wall-clock timestamps, clamps failed or pre-Y2K wall-clock reads to zero, and initializes the origin during VM initialization.
Clock exports and cross-thread validation src/jsc/virtual_machine_exports.rs, test/js/node/process/process.test.js	Clock exports use the process-wide origin. The worker test checks that its hrtime, uptime, Bun.nanoseconds(), and performance.now() readings fall between main-thread readings, and that performance.timeOrigin matches. The test terminates the worker in a finally block.

Suggested reviewers: jarred-sumner

Priority: ➖ Normal

Severity of issue fixed: Medium

Merge Risk: ⚪ Minimal · up to 42f31

Clock readings now share a process-wide origin across workers while retaining fake-timer overrides. The inspected changes reveal no issue that blocks merging.

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely describes the main change: sharing one hrtime origin across worker threads.
Description check	✅ Passed	The description explains the problem, fix, verification steps, tradeoffs, and linked issue. It does not use the exact template headings, but it provides the required information in equivalent sections…
Linked Issues check	✅ Passed	The PR addresses issue [#44221]. ProcessOrigin provides one process-wide monotonic origin. read_origin_timer uses that origin for elapsed time reads. The added worker test compares `process.hrtime…
Out of Scope Changes check	✅ Passed	The source changes implement the shared process origin and preserve overridden performance-time behavior. The added test directly verifies the linked issue's cross-worker clock behavior. No unrelated …

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Review comments at @test/js/node/process/process.test.js:
- Around line 393-407: Add a local timeout to the Worker message wait in the
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can terminate it. Clear the timer when the message arrives or the worker emits
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[robobun]

^{Updated 8:37 AM PT - Sep 29th, 2026}

@robobun, your commit 42f31f8 is building: #121621

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[robobun]

#45802 makes process.hrtime() and process.hrtime.bigint() read uv_hrtime() on every thread, so it fixes what #44221 reports. This PR still applies for process.uptime(), performance.now(), performance.timeOrigin and Bun.nanoseconds() in a Worker. The two changes compose: a simulated merge conflicts only on the import line of process.test.js, where this branch already conflicts with main. The new test here still passes on top of #45802, because it brackets each clock with readings of the same clock.