Goroutines and mutex

[Денис Мухортов]

Why are the values not incremented when declaring a structure with mutex in goroutines?
https://go.dev/play/p/bPc1bg0AvJ4

And what is the actual point in declaring something in anonymous functions, if in my experience it always works without it?

[Axel Wagner]

On Sun, Nov 28, 2021 at 4:19 PM Денис Мухортов <muhorto...@gmail.com> wrote:

Why are the values not incremented when declaring a structure with mutex in goroutines?
https://go.dev/play/p/bPc1bg0AvJ4

You have multiple problems:

1. You are passing `counter` to the goroutine as a value, making a copy

2. You have to call `wg.Add` *before* the `go` statement, otherwise it is possible that the loop finishes before any of the goroutines get scheduled, causing `wg.Wait` to immediately return

3. The playground likely doesn't actually let you consume 10s of CPU time. Normally, the emulated time of the playground means that sleeping for 10s is not a problem (as it doesn't *actually* sleep), but you are busy-looping, so you are actually taking up CPU time.

Here is a fixed version: https://go.dev/play/p/EZwW7clnORm

It still times out in the playground, though.

 

And what is the actual point in declaring something in anonymous functions, if in my experience it always works without it?

I don't understand this question.

 

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[Levieux Michel]

The problem here is you are sending a copy of counter to the anonymous function. You need to either not pass it and use the outer-scope counter directly in the function, or pass a reference to the counter to the function.

Hope this helps.

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