fix(envd): fix data race in fan-out when subscriber is removed mid-iteration#2643
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This pull request addresses a race condition in the MultiplexedChannel by creating a shallow copy of the subscribers slice before iteration, which prevents slice corruption during concurrent modifications. A regression test has been added to verify the fix and ensure stable delivery to subscribers. I have no further feedback.
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jakubno
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…teration reproducer
…eration run() snapshots the m.channels slice header under RLock and iterates after unlocking. remove() used append(channels[:i], channels[i+1:]...) which shifts the shared backing array in-place, corrupting the concurrent iteration — a subscriber can receive a value twice while another misses it entirely. Fix remove() to allocate a new backing array via slices.Concat so the old slice that run() holds remains stable. This moves the allocation to the cold path (subscriber disconnect) instead of the hot path (every fan-out delivery). Fixes: a67f983 ("fix(envd): fix fan-out deadlock when process subscriber disconnects (#2579)")
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run() snapshots the m.channels slice header under RLock and iterates after unlocking. remove() used append(channels[:i], channels[i+1:]...) which shifts the shared backing array in-place, corrupting the concurrent iteration — a subscriber can receive a value twice while another misses it entirely.
Fix remove() to allocate a new backing array via slices.Concat so the old slice that run() holds remains stable. This moves the allocation to the cold path (subscriber disconnect) instead of the hot path (every fan-out delivery).
Fixes: a67f983 ("fix(envd): fix fan-out deadlock when process subscriber disconnects (#2579)")