How to get the capacity of one channel?

Help & Support
1

Following is sample code for golang.

package main

import "fmt"

func main() {
	ch0 := make(chan string)
	fmt.Println(cap(ch0))
	ch3 := make(chan string, 3)
	fmt.Println(cap(ch3))
}

// =>
// 0
// 3

We are not the public API to get the @capacity ivar, right?

2

Crystal Channel doesn’t expose such API. Generally capacity applies to buffered channels only, where it represents the number of elements channel can hold, and it shouldn’t be confused with size. I don’t know what would be the use case where you would require such information, but you can get this info by monkey patching the Channel class.

Note: Monkey patching stdlib isn’t a good practice and is something which should be applied with extreme caution.

class Channel(T)
  def capacity : Int32
    (queue = @queue) ? queue.@capacity : 0
  end
end

And now you can get the capacity

ch0 = Channel(Nil).new
puts ch0.capacity # => 0

ch3 = Channel(Nil).new(3)
puts ch3.capacity # => 3

HIH

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3

No really, just because i found golang exposed this API, so, it probably useful for users from go, should we add this feature?

4

Yeah, sure it will be good to raise a feature request and have it open for discussion, and see if community and/or core team agrees to extend Channel class to add some api which Returns Maximum capacity of the Channel.

Reference could be GoLang API and Concurrent Ruby

1 Like
5

Just note that without an actual use case the chances of adding this will be very small.

6

I could imagine 1 use case would be gathering/monitoring channel metrics, and maybe automating channel capacity or spawning more process w/ more channels, depending on demand.

2 Likes