fix(envd): fix data race in fan-out when subscriber is removed mid-iteration#2643
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arkamar wants to merge 3 commits into
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fix(envd): fix data race in fan-out when subscriber is removed mid-iteration#2643arkamar wants to merge 3 commits into
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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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…eration run() copied only the slice header under RLock, sharing the backing array with remove(). When remove() shifted elements in-place via append(channels[:i], channels[i+1:]...), the fan-out's stale snapshot would skip one subscriber and deliver to another twice — silent stdout/stderr corruption. Deep-copy the slice under RLock so the iteration is immune to concurrent mutations. Fixes: a67f983 ("fix(envd): fix fan-out deadlock when process subscriber disconnects (#2579)")
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jakubno
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May 13, 2026
| for v := range m.Source { | ||
| m.mu.RLock() | ||
| subs := m.channels | ||
| subs := append([]*subscriber[T](nil), m.channels...) |
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| subs := append([]*subscriber[T](nil), m.channels...) | |
| subs := slices.Clone(m.channels) |
jakubno
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May 13, 2026
| @@ -54,7 +54,7 @@ func NewMultiplexedChannel[T any](buffer int) *MultiplexedChannel[T] { | |||
| func (m *MultiplexedChannel[T]) run() { | |||
| for v := range m.Source { | |||
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we should be able to move the allocation only to remove instead
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run() copied only the slice header under RLock, sharing the backing array with remove(). When remove() shifted elements in-place via append(channels[:i], channels[i+1:]...), the fan-out's stale snapshot would skip one subscriber and deliver to another twice — silent stdout/stderr corruption. Deep-copy the slice under RLock so the iteration is immune to concurrent mutations.
Fixes: a67f983 ("fix(envd): fix fan-out deadlock when process subscriber disconnects (#2579)")