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A comment on Go Things I Love: Channels and Goroutines. Parent comment

Re:Go Things I Love: Channels and Goroutines by modernerd on Tuesday January 07, 2020 @08:31AM (#21979715)
I think it's only consistent in play.golang.org because results are cached: https://blog.golang.org/playground.

If I run it locally it's not consistent:

    go run lock/main.go
    [3 0 1 2 5 4 6 9 7 8] 10⏎
    
    go run lock/main.go
    [1 5 6 7 8 0] 6⏎
    
    go run lock/main.go
    [0 3 1 2 4 5 6 7 8] 9⏎
Here's a version that does work for me: https://play.golang.org/p/b6bRb9pgIGZ

The issue is that appending to slices concurrently is not safe, so you have to use a lock around the append or similar.

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Re:Go Things I Love: Channels and Goroutines by DougBTX on Tuesday January 07, 2020 @11:03AM (#21981198)
In a way this supports the argument for the "Do not communicate by sharing memory; instead, share memory by communicating" mantra, as in a language with no compile-time checks for incorrect use of shared memory, it is very easy to get it wrong.
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Re:Go Things I Love: Channels and Goroutines by modernerd on Tuesday January 07, 2020 @11:06AM (#21981238)
Yes, it looks like the author has updated their post to say as much following the comments here.
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Re:Go Things I Love: Channels and Goroutines by iamjfu on Tuesday January 07, 2020 @04:59PM (#21985456)
I have. I didn't have time to rewrite it (I'm working, and I didn't want to take it down) so I added a few caveats. I am going to research this more and follow up again. Thanks again to everyone for the great responses. I learned a lot from the comments here.
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Re:Go Things I Love: Channels and Goroutines by empath75 on Tuesday January 07, 2020 @10:07AM (#21980568)
If you try to run a naive version of this in rust, the compiler won't even run it.

https://play.rust-lang.org/?version=stable&mode=debug&editio...

I'm a beginner at rust, but this is the version I came up with that compiles and works:

https://play.rust-lang.org/?version=stable&mode=debug&editio...

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Re:Go Things I Love: Channels and Goroutines by iamjfu on Tuesday January 07, 2020 @08:52AM (#21979853)
TIL. That's a huge flaw. Thanks so much for your response!
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Re:Go Things I Love: Channels and Goroutines by modernerd on Tuesday January 07, 2020 @09:33AM (#21980211)
Welcome! It's the same for other data structures, by the way (not just slices) — maps are not safe for concurrent writes either. (The rationale seems to be that users of the data types can choose whether to make them safe for concurrent use or not depending on the use case.)

I found this helpful: https://youtu.be/29LLRKIL_TI?t=1340

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Re:Go Things I Love: Channels and Goroutines by irq-1 on Tuesday January 07, 2020 @11:13AM (#21981319)
They added sync.Map

> Map is like a Go map[interface{}]interface{} but is safe for concurrent use by multiple goroutines without additional locking or coordination. Loads, stores, and deletes run in amortized constant time.

https://golang.org/pkg/sync/#Map

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Re:Go Things I Love: Channels and Goroutines by masklinn on Tuesday January 07, 2020 @11:10AM (#21981281)
> The rationale seems to be that users of the data types can choose whether to make them safe for concurrent use or not depending on the use case.

Also that for most uses a concurrent map is way overkill, and a thread-safe one is both costly and basically useless (hence the Java folks not keeping the thread-safety when migrating from Hashtable to HashMap).

On the other hand they're kinda shit given how awful non-builtin data structures are in Go, and how easy it is to "leak" maps between goroutines.

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Re:Go Things I Love: Channels and Goroutines by vips7L on Wednesday January 08, 2020 @07:56AM (#21990954)
Hashtable used a giant mutex when locking.. it was just slow. Especially when compared to ConcurrentHashMap.
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Re:Go Things I Love: Channels and Goroutines by shhsshs on Tuesday January 07, 2020 @07:28PM (#21986901)
Results are cached, but the main reason the example “works” is because the playground has GOMAXPROCS set to 1, meaning only a single goroutine will be running at any given point.
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Re:Go Things I Love: Channels and Goroutines by modernerd on Wednesday January 08, 2020 @02:22AM (#21989102)
That makes sense, thanks for the correction.
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