orca: fix race at producer startup #6245
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easwars
reviewed
May 2, 2023
orca/producer.go
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| mu sync.Mutex | ||
| intervals map[time.Duration]int // map from interval time to count of listeners requesting that time | ||
| listeners map[OOBListener]struct{} // set of registered listeners | ||
| hasIntervals chan struct{} // created when intervals is empty; closed and nilled when non-empty. |
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Can we use a sync.Cond instead? It seems like an appropriate use case for a condition variable. I wanted to try it out before asking for it. And it does seem simpler to use a condition variable instead of closing and recreating the channel.
easwars
approved these changes
May 3, 2023
| var min time.Duration | ||
| // recomputeMinInterval sets p.minInterval to the minimum key's value in | ||
| // p.intervals. | ||
| func (p *producer) recomputeMinInterval() { |
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Nit: s/recomputeMinInterval/recomputeMinIntervalLocked/ ?
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With #6236, an existing race was discovered (exposed in some new situations):
orca.RegisterOOBListeneris called for a SubChannel.rungoroutine is started.run()could start the OOB stream with the server at any moment now, despite no registered listeners.orca.RegisterOOBListener, the listener is registered.Between 3 and 4, we could start the stream with a request interval of 0. The server's lower bound would apply to protect it from aggressive clients, but this causes at least some tests to fail. (Note that a similar race can theoretically happen between unregistering the final listener in a producer & registering a new one, but that would require the two operations to happen at the same time, which is unusual.)
The solution is to add a channel that is created whenever there are no listeners and closed (and nilled) if it exists when a listener is registered.
RELEASE NOTES: