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The leak fixtures count live GlobalObject cells after Bun.gc(true) in each of 8 isolated files. The CI runner sets BUN_GARBAGE_COLLECTOR_LEVEL=1 and bunEnv forwards it, so every expect() matcher in the child requested one more collection. JSC runs that collection on the JS thread from the stack depth of the next allocation, and processing its conservative roots there leaves pointers to the finishing file's global in stack slots that the next file's Bun.gc(true) frames do not overwrite. That scan keeps the global alive and each later extra collection carries the retained globals forward, so the count reached 6-7 on alpine x64 with nothing pinning the globals. Run the child at level 0, so the fixture's own collections are the only ones in the run, and report the per-file counts when the bound fails.
WalkthroughChangesGC isolation tests
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Status: ready for review. This fixes the alpine x64 failure of the leak block from build 102214. How it was reproduced: the fixture files from the block, run with the release build from before #39818, keep an extra global in 27 of 40 runs with Current revision (4038c5a): CI: |
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LGTM — targeted test de-flake with the assertion strength preserved.
What was reviewed
- The
<= 4bound is unchanged; the refactor only moves it intoexpectGlobalsCollectablewithMAX_LIVE_GLOBALS = 4and adds a per-file-count failure message. { ...bunEnv, BUN_GARBAGE_COLLECTOR_LEVEL: "0" }follows the harness spread convention and matches the precedent ingc-controller-cadence.test.ts.- Confirmed no remaining
maxLiveGlobalscall sites in the tree; the #39871 conflict noted in the description is the only external caller to reconcile.
Extended reasoning...
Overview
This PR touches a single test file, test/cli/test/isolation.test.ts, and only the --isolate: collects globals pinned by leaked handles describe block. It (1) forces the spawned child to run with BUN_GARBAGE_COLLECTOR_LEVEL=0 so the fixture's own Bun.gc(true) calls are the only collections, (2) folds the per-call-site expect(await maxLiveGlobals(...)).toBeLessThanOrEqual(4) into a helper expectGlobalsCollectable that asserts the same bound and prints the per-file counts on failure, (3) hoists the magic 4 into MAX_LIVE_GLOBALS, and (4) adds a comment explaining the conservative-stack-scan mechanism that made level 1 noisy on alpine x64.
Security risks
None. Test-only change; no runtime, network, filesystem-permission, or auth surface is touched.
Level of scrutiny
Low. This is a small, mechanical de-flake of an existing test block with no production code changes. The key REVIEW.md concern for de-flakes — "keep asserting the property the original assertion protected" — is satisfied: the bound is still <= 4, and the PR description demonstrates that a pre-#39818 build (which had real Strong pins) still fails the mock and plugin cases at level 0 with the telltale 1 2 3 4 5 6 7 8 sequence. So the test is not being weakened to pass; the noise source is being removed while the signal remains.
Other factors
- The env override uses the required
{...bunEnv, KEY: value}spread pattern. - Setting
BUN_GARBAGE_COLLECTOR_LEVEL: "0"on a spawned child is an established pattern in the suite (e.g.test/js/bun/gc/gc-controller-cadence.test.tsand several others). - The root-cause analysis is thorough (async collection at arbitrary stack depth → stale stack slot survives conservative scan) and was verified with
BUN_JSC_logGC, heap snapshots, and 40-run comparisons at both levels — this is a proven mechanism, not a correlated workaround. - Grep confirms no other call sites of the renamed
maxLiveGlobalsremain; the author already flagged the pending #39871 conflict. - No prior human or bot review comments to address.
…C timer Three open PRs append cases to this block through maxLiveGlobals(), so the helper keeps its name and signature and the env change lives inside it. The child also gets BUN_GC_TIMER_DISABLE=1: at any GC level Bun.serve()'s listen hint and the idle timer request collections through GarbageCollectionController, and the serve fixture ran 8 of them per run at level 0. With both knobs BUN_JSC_logGC shows only the fixture's own 16 collections in every fixture.
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Updated 10:39 AM PT - Aug 21st, 2026
❌ @robobun, your commit 4038c5a has 1 failures in
🧪 To try this PR locally: bunx bun-pr 39875That installs a local version of the PR into your bun-39875 --bun |
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LGTM — test-only de-flake with a well-traced root cause. The inline nit about the now-vacuous caller assertions is cosmetic and can be folded into whichever of this or #39871 lands second.
Extended reasoning...
Overview
This PR touches only test/cli/test/isolation.test.ts, specifically the "collects globals pinned by leaked handles" describe block. It (1) forces the spawned child to run with BUN_GARBAGE_COLLECTOR_LEVEL=0 and BUN_GC_TIMER_DISABLE=1 so the fixture's own Bun.gc(true) calls are the only collections, (2) hoists the <= 4 bound into a MAX_LIVE_GLOBALS constant and asserts it inside maxLiveGlobals() with a per-file diagnostic message, and (3) adds a comment block explaining the conservative-stack-scan mechanism that produced the alpine x64 flake in build 102214.
Security risks
None. Test-only change; no runtime code paths, no untrusted input handling, no auth/crypto surface.
Level of scrutiny
Low-to-moderate. This is a CI de-flaking change to a test harness helper. The two questions that matter for a de-flake are (a) does it silence a real signal, and (b) are the env knobs it sets actually read. On (a): the PR description demonstrates a pre-#39818 release build still fails the mock and plugin cases at level 0 with the exact 1 2 3 4 5 6 7 8 pattern, so a real Strong/protect pin is still detected. On (b): both BUN_GARBAGE_COLLECTOR_LEVEL and BUN_GC_TIMER_DISABLE are read by src/ (env_var.rs, GarbageCollectionController.rs) and are already used the same way in gc-controller-cadence.test.ts and other tests. The {...bunEnv, KEY: ...} spread pattern matches harness convention.
Other factors
- The one finding is a nit: the seven pre-existing call sites still wrap the return in
expect(...).toBeLessThanOrEqual(4), which is now vacuous and duplicatesMAX_LIVE_GLOBALS. It cannot cause a false pass or false fail — the inner assertion at line 905 fires first with a better message. Commit e48f890 deliberately kept the return value for #39871's out-of-tree caller, and the callers themselves were not touched by this diff, so leaving the cleanup to whichever PR lands second is reasonable. - CI build 102341 shows this file green on all lanes including alpine x64; the two red lanes there are unrelated files failing on other branches too.
- No prior reviews from me on this PR.
…ctions ran The helper now runs the child with BUN_JSC_logGC and checks that the log shows the fixture's 16 full collections (17 with the VM teardown that BUN_DESTRUCT_VM_ON_EXIT adds on the ASAN lanes) and no eden collection. Without the two env knobs every case fails this on every lane: 7 eden collections from the level 1 matchers, 8 more from Bun.serve's listen hint. Before, the bound on live globals only caught them when the stack layout of one build happened to expose them. Measured at 16 full / 0 eden on the glibc release, musl release, debug ASAN and Windows canary builds.
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Actionable comments posted: 1
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Inline comments:
In `@test/cli/test/isolation.test.ts`:
- Around line 910-915: Update the collection-count assertions near the full and
eden collection calculations to derive the expected full-collection count from
the effective BUN_DESTRUCT_VM_ON_EXIT teardown setting, allowing the single
extra collection only when that setting permits it. Replace the unconditional
greater-than-or-equal and upper-bound range with an exact full count, while
keeping the zero eden-collection assertion unchanged.
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The teardown collection exists exactly when the child's env enables BUN_DESTRUCT_VM_ON_EXIT, and the helper builds that env, so it can expect 16 or 17 full collections exactly instead of a range that would also accept one stray full collection on the lanes without teardown. Measured 16 unset or "0" and 17 set, on the glibc release, musl release and debug builds.
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LGTM — test-only de-flake with a root-caused mechanism and a stronger invariant than before.
What was reviewed:
BUN_DESTRUCT_VM_ON_EXITtruthiness check matchesbun_core::env_var::string_is_truthy(case-insensitive against"", "0", "false", "no", "off"), andbunEnvspreadsprocess.envso the check reads the same value the child receives.=> FullCollection/=> EdenCollectionregex and theBUN_GC_TIMER_DISABLE/BUN_JSC_logGCknobs follow the existing pattern ingc-controller-cadence.test.ts.- The redundant caller-side
toBeLessThanOrEqual(4)assertions (my prior nit) are intentionally left in place to avoid conflicts with #39871/#39692/#39639; the PR notes the fold-in as a follow-up.
Extended reasoning...
Overview
This PR touches one file, test/cli/test/isolation.test.ts, adding +36/-2 lines inside the maxLiveGlobals helper of the "collects globals pinned by leaked handles" block. The child bun test --isolate process now runs with BUN_GARBAGE_COLLECTOR_LEVEL=0, BUN_GC_TIMER_DISABLE=1, and BUN_JSC_logGC=true; the helper then asserts an exact count of full collections (16, or 17 when BUN_DESTRUCT_VM_ON_EXIT is truthy) and zero eden collections from the JSC GC log, in addition to the existing bound on live globals. No runtime code is touched.
Security risks
None. This is a test-only change that adjusts environment variables passed to a spawned child and adds assertions on its stderr. No new inputs, no auth/crypto/permission surface.
Level of scrutiny
Low-to-medium. The change de-flakes a CI failure (build 102214, alpine x64) with a fully articulated root cause: extra GC requests from BUN_GARBAGE_COLLECTOR_LEVEL=1 (forwarded via bunEnv) and Bun.serve's listen hint leave stack slots that the conservative scanner picks up on subsequent Bun.gc(true) calls. The fix eliminates those extra collections and asserts from the GC log that only the fixture's own collections ran — a strictly stronger invariant than the old bound alone. The PR description documents verification across glibc release, musl release, debug ASAN, and Windows canary builds, and cites two green CI runs of earlier revisions on all alpine x64 shards.
Other factors
I cross-checked the implementation details: the truthiness parse of BUN_DESTRUCT_VM_ON_EXIT mirrors src/bun_core/env_var.rs:404-408 exactly (case-insensitive match against the same five strings); the => FullCollection / => EdenCollection regexes and the BUN_GC_TIMER_DISABLE / BUN_JSC_logGC knobs match the established pattern in test/js/bun/gc/gc-controller-cadence.test.ts; and bunEnv spreads process.env (harness.ts:67), so reading bunEnv.BUN_DESTRUCT_VM_ON_EXIT correctly reflects what the child receives. All review threads are resolved: my earlier nit about the now-vacuous caller-side toBeLessThanOrEqual(4) assertions was answered with a valid reason (three in-flight PRs carry those lines as diff context), and the coderabbit suggestion to assert an exact full-collection count was implemented in 4038c5a. The bug hunting system found no issues.
…nt (oven-sh#28202) The three sourcemap tests (generation, loading, loading with large files) used a `continue outer` pattern in their error-handling loops. When a duplicate/stale error was encountered, `continue outer` jumped back to reading the next stderr chunk, but any remaining lines from `str.split("\n")` that had not yet been processed were discarded because `str` was set to `""` inside the inner loop. This lost data and could cause the test to hang waiting for output that was already consumed and thrown away. Additionally, the bundler processes in the sourcemap loading tests used `stdout: "inherit"` / `stderr: "inherit"`, which could cause pipe buffer backpressure blocking the bundler. Fixes both issues with a shared `driveErrorReloadCycle` helper that: - Preserves unprocessed lines when encountering duplicate errors (uses `lines.pop()` for trailing partial lines and re-buffers remaining lines via `lines.slice(i + 1)`) - Pipes bundler stdout/stderr to `ignore` to avoid pipe buffer backpressure - Races `bundler.exited` against the reload driver for early-exit detection in the two bundler-based tests --- Verification: Format and Lint JavaScript CI checks pass. Buildkite build oven-sh#39875 still compiling at time of review. Only `test/cli/hot/hot.test.ts` changed (test-only deflake, no production code). Jarred's CHANGES_REQUESTED about the nonce mechanism was addressed in commit 50f3f4e (nonce removed). No TODO/FIXME/HACK in added lines. The driveErrorReloadCycle helper correctly preserves partial line fragments and remaining unprocessed lines, prevents double onReload calls via the triggered flag, and uses Buffer.alloc per test/CLAUDE.md convention. --------- Co-authored-by: Alistair Smith <hi@alistair.sh>
Problem
test/cli/test/isolation.test.tswent red on alpine x64 in build 102214. All 7 cases failed on both attempts:expect(received).toBeLessThanOrEqual(expected),Expected: <= 4,Received: 6.GlobalObjectcells afterBun.gc(true)in 8 isolated files, but the child ran other collections too.bunEnvforwards the CI runner'sBUN_GARBAGE_COLLECTOR_LEVEL=1, at whichExpect::post_match(src/runtime/test_runner/expect.rs:1735) requests one after every matcher. At any level,Bun.serve()'s listen hint (src/runtime/server/mod.rs:3172) and the idle GC timer request one throughGarbageCollectionController.Bun.gc(true)frames do not overwrite, so the conservative scan keeps the global alive. Each later extra collection carries the retained globals forward.Fix
maxLiveGlobalsspawns the child withBUN_GARBAGE_COLLECTOR_LEVEL=0andBUN_GC_TIMER_DISABLE=1, asgc-controller-cadence.test.tsdoes, and withBUN_JSC_logGC. It asserts that the log shows exactly the fixture's 16 full collections, plus the one teardown collection when the child's env enablesBUN_DESTRUCT_VM_ON_EXIT(the ASAN lanes do), and no eden collection.Strongor a protect that pins a global survives the fixture's own collections, and a release build from before bun test --isolate: stop finished files from pinning their global via mocks and plugins #39818 still fails the mock and plugin cases. The helper now prints the count each file saw (a pin reads1 2 3 4 5 6 7 8). Its name, signature and callers are unchanged, so perf_hooks: stop the event-loop-delay monitor when bun test --isolate retires its realm #39871, s3: fail a streaming upload at VM teardown instead of leaking it #39692 and fetch: drop the upload and drain hop refs at VM teardown #39639, which add cases through it, land in any order.bun bd test test/cli/test/isolation.test.ts, 27 pass, also with the ASAN lane's environment. Measured 16 full / 0 eden on the glibc release, musl release, debug ASAN and Windows canary builds.Background
bun test --isolateruns each file in a new global on one VM. The swap unprotects the old global, so a full collection frees it unless a handle holds it.Structure.Bun.gc(true)is always a full collection. These heaps never reach JSC's own allocation budget, so an eden collection in the log was requested by Bun code.GarbageCollectionController(src/jsc/GarbageCollectionController.rs) owns Bun's idle GC timer. Itsperform_gcalso serves the listen hint.BUN_GC_TIMER_DISABLEturns both off.Notes
Heap::requestCollectiongives the mutator the conn andHeap::collectInMutatorThreadruns the cycle at the nextstopIfNecessary(). The fixture's ownBun.gc(true)calls always run from the same position, below the point the scan starts at, so they leave nothing for the next scan.1 2 2 3 2 3 2 3to1 2 2 2 2 2 2 2with the knob. The idle timer did not fire in any run measured here, but a slow run can reach its 1 s interval, and the same knob covers it.BUN_DESTRUCT_VM_ON_EXITis enabled. The test mirrors bun's parsing of that variable (truthy unless "", "0", "false", "no" or "off"). Measured 16 unset or "0" and 17 set on the glibc release, musl release and debug builds. The lower bound also proves the log is on, otherwise the eden check would pass for nothing.BUN_JSC_randomIntegrityAuditRate=1.0(also set by the runner) andulimit -s unlimited(set on the alpine agents) do not change the counts.1 2 2 2 2 2 2 2, within the bound.toBeLessThanOrEqual(4)is now redundant with the helper's assertion and can be folded in once those PRs land.[stamp-90s] gate passed · iteration 0 · 1 files touched
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