Mutex is there but I need the permits logic of sem...

# coroutines

[minivac]

Mutex is there but I need the permits logic of semaphores

[gildor]

Could you show some example of code where you need it

[gildor]

Probably this thread also may be interesting for you
https://kotlinlang.slack.com/archives/C1CFAFJSK/p1549980138040900

[minivac]

use case is a count latch

[gildor]

CountDownLatch is mostly not needed for coroutines

[minivac]

so it's exactly a channel, multiple possible producers, one consumer that waits for jobs to close resource

[gildor]

could you show some self contained example, probably there is better solution for coroutines

[minivac]

it's classic reader writer problem

[gildor]

also related topic about CountDownLatch in coroutines
https://github.com/Kotlin/kotlinx.coroutines/issues/59

[minivac]

so it's quite easy to implement with something that can count active writers, in Java that would be quick to implement with semaphores

[minivac]

or a count latch

[minivac]

I have my own mini wrapper to create a suspending semaphore, it's really just a wrapped channel

[minivac]

wanted to know if there is something already done in kotlin coroutines library with same functionality

[gildor]

I would like to see your current implementation, hard to say without example

[minivac]

oh well, thanks for the link, looks like I actually need a Phaser

[minivac]

didn't know about that structure

[minivac]

fits exactly

[minivac]

class SuspendSemaphore(permits: Int = 0,
                                capacity: Int = Channel.UNLIMITED) {

    private val channel = Channel<Unit>(capacity)

    init {
        repeat(permits) {
            channel.offer(Unit)
        }
    }

    suspend fun acquire() {
        channel.receive()
    }

    fun release() {
        channel.offer(Unit)
    }
}

[minivac]

sure, it's super simple to implement a semaphore with a channel

[cbruegg]

It might be nice to have this in kotlinx.coroutines.

[Jonathan]

It might be nice to have this in kotlinx.coroutines.

As @gildor said, it is not needed with coroutines. (more explanation by @elizarov in https://github.com/Kotlin/kotlinx.coroutines/issues/59).

[Jonathan]

A read-write mutex may be added in kotlinx.coroutines though: https://github.com/Kotlin/kotlinx.coroutines/pull/408