fix(runtime): bound promise tracker to prevent OOM#143
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V3RON merged 4 commits intoJul 3, 2026
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The promise tracker retained a record (with a captured stack) for every promise created via the global constructor and only released it on settle. Records were never drained between tests/files and had no size bound, so an app that continuously creates promises that are abandoned before they settle (animations, requestAnimationFrame loops, polling, async data-binding) grew the JS heap linearly until 'JavaScript heap out of memory'. Release a promise's record as soon as the promise is garbage-collected (via FinalizationRegistry) and cap the number of retained records as a synchronous backstop, keeping memory bounded regardless of app bridge/render traffic. Fixes callstackincubator#142
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Replace runtime reproduction tests with a playground harness regression that verifies abandoned promises are reclaimed after GC.
The runtime unit tests continue to cover promise tracker behavior, while the playground harness GC assertion depends on non-deterministic FinalizationRegistry scheduling.
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Description
Fixes an unbounded memory leak in the runtime promise tracker (
@react-native-harness/runtime) that could exhaust the JS heap (JavaScript heap out of memory) during long runs.The tracker recorded every promise created via the global constructor — plus a captured stack — and only released it when the promise settled. Records were never drained between tests/files and had no size bound. Any app that keeps creating promises that are abandoned before they settle (animations,
requestAnimationFrameloops, polling, async data-binding) therefore grew the heap linearly with elapsed render time until the process aborted.The fix:
FinalizationRegistry— releases a promise's tracking record as soon as the promise itself is garbage-collected. A collected promise can no longer settle or keep anything pending, so retaining its record (and stack) is pure waste. This is the root-cause fix.MAX_TRACKED_PROMISES = 10_000, evict-oldest)— a synchronous backstop for when GC can't keep up under heavy allocation pressure. Timeout diagnostics only ever display 10 pending promises, so this is invisible in normal use.Related Issue
Fixes #142
Context
The tracker only exists to report which promises are still pending when a test times out. It does not need the full session history — only currently-live, unsettled promises. Both changes preserve that behavior: live pending promises stay tracked, while collected/abandoned ones are released and the total is bounded.
No public API changes. The existing
clearTrackedPromises()/getPendingPromises()surface is unchanged.Testing
promise-tracker-leak.repro.test.ts— a regression guard that fails on the old code (30k records retained, never drained) and passes now (bounded).promise-tracker-oom.repro.test.ts— an opt-in (RN_HARNESS_OOM_REPRO=1) reproduction that drives the real tracker under a low heap cap. Before: RSS climbs linearly toFATAL ERROR: Reached heap limit ... JavaScript heap out of memory. After: 50M abandoned promises under--max-old-space-size=512complete cleanly with RSS pinned at the cap.packages/runtimesuite compared against a pristine baseline: the leak repro flips fail→pass and there are no new failures (the pre-existing environment-specific failures are unchanged by this PR).