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Use shared FSEvents streams #4447

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Use shared FSEvents streams #4447

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822798a
Use shared FSEvents streams
jakebailey Jun 25, 2026
c2640d4
Try single FSEvents stream before chunking
jakebailey Jun 25, 2026
2f755c6
Document shared FSEvents streams
jakebailey Jun 25, 2026
e695074
Scope shared FSEvents callbacks to stream paths
jakebailey Jun 25, 2026
6e9ef2a
Scope FSEvents overflow routing
jakebailey Jun 25, 2026
3a1423e
Route FSEvents callbacks without backend snapshot
jakebailey Jun 25, 2026
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10 changes: 10 additions & 0 deletions internal/fswatch/CHANGES.md
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Expand Up @@ -127,6 +127,16 @@ can't starve event delivery on any of the others. In practice most callers will
only ever use one backend (`Default()`), so this mainly matters for processes
that mix backends, but the cost of the split is essentially nothing.

### Shared FSEvents streams

Upstream opens one macOS FSEventStream per subscription. Go's FSEvents backend
shares streams across all logical directory watches in a backend instance. The
fast path attempts one stream containing every active physical watch root; if
that stream cannot be started, the backend retries with bounded path chunks.
Events from shared streams are routed back to matching logical watches by path,
so non-recursive and per-subscriber ignore semantics are preserved while using
far fewer system-wide FSEvents stream slots.

## New backends

**fanotify** (Linux, kernel ≥ 5.13) is the default on Linux when available. It
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