I can t come out of reading a channel loop Its a hard block

Question

I can t come out of reading a channel loop Its a hard block on the execution

groostav · Answer

gt I cant come out of a channel loop meaning a for each loop on a receive channel Yeah it only exits when the channel has completed You might consider using a `withTimeoutOrNull` + `receieve` or `select channel onReceieve ` instead of a for each loop if you need more control gt Its a hard block on the execution Certainly not the caller is suspended and there s no execution in a channel per se Remember most of the time you wire a producer up to your channel that you re then consuming When the consumer attempts to read an element it does so fully ~asynchronous~ concurrently with the producer

asad.awadia · Answer

How do i get to the next line from the read from a channel without sending a close

asad.awadia · Answer

Lets say theres a bunch of coroutines sending a string to a channel can i stop the infinite loop over reading the channel And get to the next line without sending close because I cant guarantee that the close will be sent after all the values have been sent

groostav · Answer

I m not sure what you mean by next line but cant you detect your cercomstance and `break` ``` for element in foreverChannel if state + element gt threshold break ```

asad.awadia · Answer

Is that how you re supposed to do it though

asad.awadia · Answer

I can but that looks unclean and unkotlin like

groostav · Answer

so you do have to ask about cancellation if the consumer doesnt ever consume any more elements from `foreverChannel` do you want it to cancel that channel

groostav · Answer

if that is true then `consumeEach` is what you want and if thats true you can use the standard functional `first` combinator

groostav · Answer

ie

groostav · Answer

``` val result = foreverChannel first state + it gt threshold ```

groostav · Answer

that will cause `foreverChannel` to be cancelled after the first element that matches that criteria which causes your producers to all get signalled next time they try to produce

asad.awadia · Answer

Hmm thinking face

asad.awadia · Answer

Surprised kotlin doesn t already have syntactic sugar for this

asad.awadia · Answer

In go you can create a buffered channel and then read that many elements in a loop

asad.awadia · Answer

I guess I could do that

asad.awadia · Answer

Is it bad to have a channel read n elements from it and then proceed and not ever send a close

groostav · Answer

I think its a problem only if you dont have reasonable assurances that there are producers and consumers as long as there will be another consumer that s taking elements n+1 until the close signal But I just had this same thought what I d really like is a `take n ` that doesn t cancel the channel after receiving those elements gt quick point you cant `close` a `ReceiveChannel` you can only `cancel` it Producers `close` the `SendChannel`s If you think about your program as being a kind of parser then trying to look ahead on a channel some number of tokens messages without cancelling or closing the channel is totally reasonable

Vsevolod Tolstopyatov [JB] · Answer

We don t have a built in mechanism that loops `n` times and then returns without cancelling a channel otherwise you can use `take` If you think this is a frequent use case that keeps popping here and there feel free to create an issue on github

Vsevolod Tolstopyatov [JB] · Answer

in you project you can just create a specific extension ``` suspend inline fun lt E gt ReceiveChannel lt E gt iterate limit Int action suspend element E gt Unit var consumed = 0 for element in this action element if ++consumed == limit break ```

asad.awadia · Answer

< Vsevolod Tolstopyatov JB > thank you Much appreciated

asad.awadia · Answer

I read Roman s answer on stack Overflow that not closing a channel is nbd that s still applies

asad.awadia · Answer

Thats my biggest concern reading from a channel and then just moving on without closing it

gildor · Answer

In this case channel will leak

asad.awadia · Answer

If someone writes to it

asad.awadia · Answer

What if nothing will write to it

gildor · Answer

if this channel blocks some coroutine like in case of `produce`

gildor · Answer

it depends on channel implementation it can be garbage collected if there are no more links on this channel

gildor · Answer

it depends on implementation for example ``` val channel = produce while true send something ``` if you never close this channel it will leak coroutine and channel but it s not so bad because now you can call produce only in CoroutineScope this channel will be closed together with scope