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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"AbortSignal.any(): observed composites still accumulate in a long-lived source's kDependantSignals after #62367 (not GC-pruned)","articleBody":"Follow-up to #62363 / #62367.\n\n#62367 (\"defer `AbortSignal.any()` following\") stops **listener-less** composites from following their sources eagerly. But a composite that **is** observed (has an `abort` listener) still follows its sources, and when one of those sources is **long-lived**, the composite's entry accumulates in that source's `kDependantSignals` and is **not pruned even by a forced `global.gc()`**. `size` grows monotonically for as long as the process runs.\n\nReproduces on **v24.18.0** (which contains #62367), back on **v22.12.0**, and on the latest **v26.5.0** (`v8 14.6`).\n\n> **Note (edited after #64481):** My original wording said \"aborting or not doesn't matter; both leak\" but only attached the aborted repro. Both cases are shown below now (Repro A = aborted, Repro B = never aborted). They have different causes — see the Update at the bottom.\n\n### Version\n\n`v24.18.0` (`v8 13.6.233.17-node.50`), `v22.12.0` (`v8 12.4.254.21-node.21`), and `v26.5.0` (`v8 14.6.202.34-node.24`).\n\n### Platform\n\nmacOS (darwin), installed via nvm.\n\n### Subsystem\n\n`abortcontroller` / `lib/internal/abort_controller.js`\n\n### Repro A — composite is aborted\n\n```js\n// node --expose-gc reproA.mjs [shared|fresh]     (shared = long-lived source)\nconst mode = process.argv[2] || 'shared';\nconst longLived = new AbortController(); // never aborted; e.g. an app-lifetime \"shutdown\" signal\nconst N = 500_000;\n\nconst kDep = () => Object.getOwnPropertySymbols(longLived.signal)\n  .find((s) => s.toString() === 'Symbol(kDependantSignals)');\n\nfor (let i = 1; i \u003c= N; i++) {\n  const source = mode === 'shared' ? longLived : new AbortController();\n  const perReq = new AbortController();\n  const composite = AbortSignal.any([perReq.signal, source.signal]);\n  composite.addEventListener('abort', () => {}); // \"observed\": composite follows its sources\n  perReq.abort();                                 // settle, then discard composite/perReq\n  if (i % 100_000 === 0) {\n    globalThis.gc();                              // force a full GC\n    const sym = kDep();\n    console.log(`${i} iters | longLived.kDependantSignals.size = ${sym ? longLived.signal[sym].size : 0}`);\n  }\n}\nconsole.log(`node ${process.version} | v8 ${process.versions.v8} | mode=${mode}`);\n```\n\n```\n### mode=shared (long-lived source) ###\n100000 iters | longLived.kDependantSignals.size = 100000\n...\n500000 iters | longLived.kDependantSignals.size = 500000\n\n### mode=fresh (control) ###\n... size = 0 (flat)\n```\n\n### Repro B — composite is never aborted (normal-completion path)\n\n```js\n// node --expose-gc reproB.mjs\nconst longLived = new AbortController();\nconst N = 500_000;\nconst kDep = () => Object.getOwnPropertySymbols(longLived.signal)\n  .find((s) => s.toString() === 'Symbol(kDependantSignals)');\n\nfor (let i = 1; i \u003c= N; i++) {\n  const perReq = new AbortController();\n  const composite = AbortSignal.any([perReq.signal, longLived.signal]);\n  composite.addEventListener('abort', () => {}); // observed\n  // no abort() — the \"request\" just completes and the composite is dropped\n  if (i % 100_000 === 0) {\n    globalThis.gc();\n    const sym = kDep();\n    console.log(`${i} iters | longLived.kDependantSignals.size = ${sym ? longLived.signal[sym].size : 0}`);\n  }\n}\nconsole.log(`node ${process.version} | v8 ${process.versions.v8} | never-aborted`);\n```\n\n```\n### v26.5.0 — observed, never aborted ###\n100000 iters | longLived.kDependantSignals.size = 100000\n...\n500000 iters | longLived.kDependantSignals.size = 500000\n```\n\n### Expected behavior\n\nPer the DOM Standard, an `AbortSignal`'s **dependent signals** and **source signals** are each *\"a weak set\"*. Entries for composites that can no longer usefully fire should not accumulate indefinitely on a long-lived source.\n\n### What you see instead\n\n`kDependantSignals.size` on the long-lived source grows monotonically and is not reclaimed by a forced full GC. A fresh-source control (Repro A `mode=fresh`) stays flat at 0.\n\n### Version coverage\n\nBoth repros reproduce on v22.12.0, v24.6.0, v24.13.1, v24.18.0, and v26.5.0.\n\n---\n\n### Update (after #64481)\n\nThanks @bitpshr. The root cause for **Repro A** is `gcPersistentSignals` retaining the aborted composite — the abort path marks it aborted but never drops it, so on a long-lived source it's retained forever and its `WeakRef` never gets pruned. #64481 fixes that by dropping transitively-aborted dependents from `gcPersistentSignals`, which is the clear, actionable bug here.\n\nTo correct my original \"aborting or not doesn't matter\" wording — the two cases differ:\n\n- **Repro A (aborted):** the bug #64481 fixes. ✅\n- **Repro B (never aborted):** still accumulates (verified on v26.5.0 above). But I suspect this one may be **by design**: an observed composite whose source is still alive has to remain reachable so it can fire if the source aborts later, so `gcPersistentSignals` can't drop it while the source lives (cf. #64342). Flagging it only so it's a conscious call whether B is in-scope or expected — if it's expected/\"remove the listener\", that's a fine resolution and #64481 covers the actionable part.\n","author":{"url":"https://github.com/denghongcai","@type":"Person","name":"denghongcai"},"datePublished":"2026-07-13T17:26:45Z","url":"https://github.com/nodejs/node/issues/64476"}