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Comment by serialx | Hacker News Reader

PSA: You can also use singleflight[1] to solve the problem. This prevents the thundering herd problem. Pocache is an interesting/alternative way to solve thundering herd indeed!

[1]: https://pkg.go.dev/golang.org/x/sync/singleflight

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I'm confused by the decision in DoChan to return a channel (instead of accepting one supplied by the caller) and then, given that, also not to close that channel (is something else going to be sent to the channel in the future?). Both seem like strange/unnecessary design decisions.

Returning a channel avoids questions of what happens if sending to a caller-supplied channel blocks. DoChan returns a channel with a single-element buffer, so a single send to the channel will always succeed without blocking, even if the caller has lost interest in the result and discarded the channel.

DoChan doesn't close the channel because there isn't any reason to do so.

A non-blocking send would work just as well for that issue, is a standard part of the language, and would support user-supplied channels, but it would still be at risk of panicking when sending to a closed channel. I think there ought to be a safe way to send to a closed channel, but the language authors disagree, so that's not really on the library authors (though they could still recover from the panic).

However, not closing the channel you specifically chose to control all sending to is just lazy/rude. Even though the caller should receive from the channel once and then forget about it, closing the channel after sending would prevent incorrect subsequent receives from hanging forever.

All this having been said, contributing to these libraries seems better than complaining about them, but I don't know how the golang.org/x stuff is maintained; looks like this one is here: https://github.com/golang/sync

Closing the channel is pointless. I don't understand why people get obsessive about closing channels.

It's not needed by the garbage collector, it's not good practice. It's explicitly called out in the official go guide as unnecessary most of the time. [0]

If you have a channel that is only used a single time and then discarded, closing it is literally just wasting CPU cycles. And definitely not "lazy/rude".

[0] https://go.dev/tour/concurrency/4

I illustrated why closing the channel is beneficial: the consumer of the channel may not be using it properly. Reading the unclosed channel more than once will hang. A stuck goroutine is rarely desirable. The cost of closing a channel is similar to the cost of bounds checking; it may not be free, but it's usually worth it. Agreed that this has no benefit to the garbage collector. I also think this is a pretty clear example of when you should close a channel, as pointed out by the Tour: to inform the consumer that no more values will ever be forthcoming.

A non-blocking send doesn't work in this case. Consider: User provides DoChan an unbuffered channel, and then reads a value from it. If the send is nonblocking and occurs before the user reads from the channel, the value is lost.

thank you for the recommendation, was a good read as well. I could even use it to replace how I'm handling the call suppression/debounce mechanism. Though I think Pocache does 1 extra thing, which is to keep the cache updated before it expires, i.e. for keys which are frequently fetched it'd serve up to date data always from the cache. If we only relied on call suppression, then the concurrent requests would just have to wait during the update stage, or the read-through mechanism would keep hitting the main database.

interesting, thanks for that. I'll check it out

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