windows: lock watch field updates against concurrent WatchList#749
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…ify#709) WatchList() iterates watchEntry.names and reads watchEntry.mask under w.mu, but the I/O thread (addWatch/remWatch/deleteWatch and the rename and remove paths in readEvents) mutated those same fields without the lock. The race detector flagged the mask field; the names map mutation is the more dangerous case since concurrent map write + iterate panics at runtime. Hold w.mu around all writes to mask/names. deleteWatch snapshots the map and mask under the lock and sends events outside it to avoid blocking on the user-facing Events channel while holding the mutex. Regression from v1.9.0.
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Fixes #709. Calling
WatchList()concurrently withAdd()/Remove()on Windows raced with the I/O thread mutatingwatchEntry.maskandwatchEntry.namesoutside the lock; the race detector caught themaskaccess but the more dangerous case is concurrent map iteration vs. write onwatchEntry.names, which can panic at runtime. Holdw.muaround all writes to those fields (addWatch,remWatch,deleteWatch, and the rename/remove paths inreadEvents).deleteWatchsnapshots the map and mask under the lock and then callssendEventoutside it to avoid blocking on the Events channel while holding the mutex. AddsTestWatchListRaceas a regression test.