fix(server): stop idle private-memory growth from immortal parent spans - #5411
fix(server): stop idle private-memory growth from immortal parent spans#5411Benchance wants to merge 3 commits into
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Long-lived forkParked roots and PortDiscovery poll loops were inheriting Effect ParentSpan from short-lived startup/make spans. Nested hot-path spans (secret reads, idle poll ticks) kept parenting under those immortal spans and drove ~25-30MB/h private growth while idle. Detach ambient ParentSpan in forkParked, untrace idle port polls and secret gets, and drop PortDiscovery.make's wrapping span. Co-authored-by: Cursor <cursoragent@cursor.com>
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Co-authored-by: Cursor <cursoragent@cursor.com>
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| Effect.gen(function* () { | ||
| const activation = yield* ServerActivation; | ||
| const detached = withoutAmbientParentSpan(effect); |
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🟠 High src/serverActivation.ts:25
withoutAmbientParentSpan casts the context after removing Tracer.ParentSpan back to Context.Context<NoInfer<R>>, so the return type still claims to satisfy effects whose environment explicitly includes Tracer.ParentSpan. If an effect passed to withoutAmbientParentSpan (or to forkParked, which wraps every input with it) directly uses Tracer.ParentSpan, the code type-checks but the forked fiber fails at runtime with Service not found because the service was removed from the child context. The cast masks a missing-service defect rather than surfacing it as a type error. Consider constraining the input type so Tracer.ParentSpan cannot appear in R.
- (context) => Context.omit(Tracer.ParentSpan)(context) as Context.Context<NoInfer<R>>,
+ (context) => Context.omit(Tracer.ParentSpan)(context) as Context.Context<Exclude<NoInfer<R>, Tracer.ParentSpan>>,
+ // Note: this cast is unsafe if R explicitly requires Tracer.ParentSpan;
+ // callers should ensure the input does not use that service directly.🤖 Copy this AI Prompt to have your agent fix this:
In file @apps/server/src/serverActivation.ts around lines 25-27:
`withoutAmbientParentSpan` casts the context after removing `Tracer.ParentSpan` back to `Context.Context<NoInfer<R>>`, so the return type still claims to satisfy effects whose environment explicitly includes `Tracer.ParentSpan`. If an effect passed to `withoutAmbientParentSpan` (or to `forkParked`, which wraps every input with it) directly uses `Tracer.ParentSpan`, the code type-checks but the forked fiber fails at runtime with `Service not found` because the service was removed from the child context. The cast masks a missing-service defect rather than surfacing it as a type error. Consider constraining the input type so `Tracer.ParentSpan` cannot appear in `R`.
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Addressed in 17580be — return type is now Effect.Effect<A, E, Exclude<R, Tracer.ParentSpan>> with a matching context cast, so the stripped env is reflected in the type.
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Pull request overview
Fixes idle private-memory growth in the desktop/server process by preventing long-lived fibers (parked roots + background pollers) from inheriting short-lived startup Tracer.ParentSpan context, and by reducing tracing work on hot/idle paths.
Changes:
- Add
withoutAmbientParentSpanand apply it inforkParkedto detach inheritedTracer.ParentSpanfor long-lived roots. - Reduce tracing overhead on idle/background loops (PortDiscovery polling, secret reads) and remove the
PortDiscovery.makewrapping span. - Add a focused unit test validating that
withoutAmbientParentSpanclears inheritedTracer.ParentSpanwithout affecting sibling effects.
Reviewed changes
Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.
Show a summary per file
| File | Description |
|---|---|
| apps/server/src/serverRuntimeStartup.ts | Documents why parked startup roots must detach ambient ParentSpan to avoid pinning startup spans. |
| apps/server/src/serverActivation.ts | Introduces withoutAmbientParentSpan and applies it to all forkParked forks. |
| apps/server/src/serverActivation.test.ts | Adds a unit test asserting ParentSpan detachment behavior. |
| apps/server/src/preview/PortScanner.ts | Detaches the poll fiber from ambient parent spans and disables tracing in the poll loop; removes PortDiscovery.make span wrapper. |
| apps/server/src/auth/ServerSecretStore.ts | Disables tracing for frequent secret reads to reduce idle trace volume and span retention. |
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| expect(stillHasParent).toBe(true); | ||
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| const stripped = Context.omit(Tracer.ParentSpan)(Context.make(Tracer.ParentSpan, ambient)); | ||
| expect(Context.getOption(stripped, Tracer.ParentSpan)._tag).toBe("None"); |
| // Single layer-scoped polling fiber. Ticks are no-ops when no client is | ||
| // currently retained, so the cost is one Ref.get every POLL_INTERVAL. | ||
| yield* Effect.forkScoped(pollTick().pipe(Effect.repeat(Schedule.spaced(POLL_INTERVAL)))); | ||
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| // currently retained. Run detached from any ambient ParentSpan (e.g. | ||
| // PortDiscovery.make) and without tracing idle no-ops — otherwise every | ||
| // 3s tick parents under an immortal span and grows server private memory. | ||
| yield* Effect.forkScoped( | ||
| withoutAmbientParentSpan( | ||
| pollTick().pipe( | ||
| Effect.repeat(Schedule.spaced(POLL_INTERVAL)), | ||
| Effect.withTracerEnabled(false), | ||
| ), | ||
| ), | ||
| ); |
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Good catch — fixed in 17580be. Idle early-return now sits outside Effect.fn("PortDiscovery.pollTick") so no-op ticks create no span, and the blanket withTracerEnabled(false) on the poll loop is gone so active scans still get traced. ParentSpan detach stays via withoutAmbientParentSpan.
ApprovabilityVerdict: Needs human review 1 blocking correctness issue found. This memory-leak fix modifies span/tracing behavior for long-lived server processes. An unresolved high-severity comment identifies a type cast that could mask runtime 'Service not found' errors, which warrants human review to ensure correctness. You can customize Macroscope's approvability policy. Learn more. |
Keep active PortDiscovery polls traced, tighten withoutAmbientParentSpan's R, and use Option.isNone in the test. Co-authored-by: Cursor <cursoragent@cursor.com>
Summary
forkParkedroots and the PortDiscovery poll loop were inheriting EffectParentSpanfrom short-lived startup/makespans, so hot-path nested spans kept parenting under immortal spans.ParentSpaninforkParked, untrace idle port polls + secret gets, and dropPortDiscovery.make's wrapping span.Test plan
vp test run src/serverActivation.test.ts src/preview/PortScanner.test.ts(apps/server)server.trace.ndjsonno longer floods withPortDiscovery.pollTick/ServerSecretStore.getunderstartup.phase=reactors.startFixes #5410
Note
Medium Risk
Changes tracing and span parentage for all forkParked background work and port/secret hot paths; runtime behavior is unchanged but observability under startup traces will look different.
Overview
Addresses idle Private memory creep (#5410) by stopping long-lived server fibers from inheriting short-lived startup
ParentSpanvalues, which kept parent spans and nested trace data alive indefinitely.Adds
withoutAmbientParentSpaninserverActivation.tsand runs allforkParkedroots through it so background reactors no longer parent under immortal startup spans. The PortDiscovery poll loop uses the same helper, moves the retain-count idle check outsideEffect.fnso no-op ticks do not create spans, and drops the wrapping span onPortDiscovery.make.ServerSecretStore.getswaps its named span forwithTracerEnabled(false)to avoid high-frequency secret reads under startup traces. A unit test asserts that ambientParentSpanis stripped while normal effects still see it.Reviewed by Cursor Bugbot for commit 17580be. Bugbot is set up for automated code reviews on this repo. Configure here.
Note
Stop idle private-memory growth from immortal parent spans in background fibers
withoutAmbientParentSpanhelper in serverActivation.ts that stripsTracer.ParentSpanfrom an effect's context, preventing long-lived forked fibers from holding a reference to a parent span.withoutAmbientParentSpaninforkParkedso all long-running roots it forks no longer inherit an ambient parent span.PortDiscoverypolling in PortScanner.ts so idle no-op ticks skip span creation entirely, and the background polling fiber runs without an inherited parent span.ServerSecretStore.getin ServerSecretStore.ts instead of creating a named span per call.ServerSecretStore.get, or thePortDiscovery.makeandforkParkedroots.Macroscope summarized 17580be.