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control/controlclient: flesh out a recently added comment

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Updates tailscale/corp#26058

Change-Id: Ib46161fbb2e79c080f886083665961f02cbf5949
This commit is contained in:
Brad Fitzpatrick 2025-01-30 07:23:36 +00:00 committed by Brad Fitzpatrick
parent ed8bb3b564
commit 0ed4aa028f
1 changed files with 11 additions and 6 deletions
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17
control/controlclient/auto.go
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@ -620,12 +620,17 @@ func (c *Auto) sendStatus(who string, err error, url string, nm *netmap.NetworkM
} }
} }
c.observer.SetControlClientStatus(c, *newSt) c.observer.SetControlClientStatus(c, *newSt)
// Best effort stop retaining the memory now that
// we've sent it to the observer (LocalBackend). // Best effort stop retaining the memory now that we've sent it to the
// We CAS here because the caller goroutine is // observer (LocalBackend). We CAS here because the caller goroutine is
// doing a Store which we want to want to win // doing a Store which we want to win a race. This is only a memory
// a race. This is only a memory optimization // optimization and is not for correctness.
// and is not for correctness: //
// If the CAS fails, that means somebody else's Store replaced our
// pointer (so mission accomplished: our netmap is no longer retained in
// any case) and that Store caller will be responsible for removing
// their own netmap (or losing their race too, down the chain).
// Eventually the last caller will win this CAS and zero lastStatus.
c.lastStatus.CompareAndSwap(newSt, nil) c.lastStatus.CompareAndSwap(newSt, nil)
}) })
} }