Summary

• defer following source signals for AbortSignal.any() until the composite is observed
• keep composite state in sync via lazy refresh and follow paths
• unregister fired timeout signals from clearTimeoutRegistry to reduce timeout churn retention
• add regression coverage for long-lived and timeout churn cases

Problem

AbortSignal.any() eagerly registered listener-less composites as dependants of their source signals. With a long-lived source, repeated AbortSignal.any([source]) calls accumulated in kDependantSignals and retained memory (#62363).

While investigating broader AbortSignal churn, timeout-only churn also kept timeout finalization registry entries alive after timers had fired, which delayed cleanup.

What Changed

AbortSignal.any()

• listener-less composites no longer follow source signals eagerly
• composites follow their sources only when observed
• composite state is refreshed lazily when reading aborted, reason, or throwIfAborted()

AbortSignal.timeout()

• fired timeout signals now unregister themselves from clearTimeoutRegistry
• this releases timeout churn bookkeeping sooner after the timer has fired

Results

#62363 repro

• out/Release/node stayed flat through 2,000,000 iterations
• kDependantSignals stayed at 0

Timeout churn

AbortSignal.timeout(1)
start {"rss":"45.67","heap":"3.49"}
before-gc {"rss":"153.39","heap":"79.54"}
after-gc {"rss":"164.55","heap":"23.15"}
after-1-immediate {"rss":"160.23","heap":"6.28"}
after-50ms {"rss":"158.67","heap":"6.26"}

AbortSignal.any([AbortSignal.timeout(1)])
start {"rss":"45.72","heap":"3.49","handles":0}
before-gc {"rss":"133.58","heap":"32.48","handles":2}
after-gc {"rss":"135.30","heap":"7.85","handles":2}
after-1-immediate {"rss":"135.31","heap":"5.06","handles":2}
after-50ms {"rss":"135.31","heap":"5.04","handles":2}

AbortSignal.timeout(1)
start {"rss":"45.52","heap":"3.49"}
before-gc {"rss":"66.55","heap":"6.84"}
after-gc {"rss":"67.19","heap":"3.96"}
after-1-immediate {"rss":"67.20","heap":"3.88"}
after-50ms {"rss":"67.23","heap":"3.87"}

AbortSignal.any([AbortSignal.timeout(1)])
start {"rss":"45.58","heap":"3.49","handles":0}
before-gc {"rss":"73.52","heap":"9.82","handles":2}
after-gc {"rss":"74.22","heap":"4.01","handles":2}
after-1-immediate {"rss":"74.22","heap":"3.91","handles":2}
after-50ms {"rss":"74.22","heap":"3.90","handles":2}

Notes

The same-tick fresh AbortController microbenchmark from #54614 still shows heap growth until the next turn. That appears to be due to WeakRef cleanup semantics rather than long-lived source retention: the heap drops back after a setImmediate() and the weak references clear on the next turn.

Testing

• python3 tools/test.py test/parallel/test-abortsignal-any.mjs test/parallel/test-abort-controller-any-timeout.js test/parallel/test-abortsignal-drop-settled-signals.mjs test/parallel/test-abortsignal-timeout-memory.js test/parallel/test-abortcontroller.js

Fixes: #62363
Refs: #54614