Example of select on mutext.onLock

SimpleMutexSelect.kt

package org.athenian.select

import kotlinx.coroutines.delay
import kotlinx.coroutines.launch
import kotlinx.coroutines.runBlocking
import kotlinx.coroutines.selects.select
import kotlinx.coroutines.sync.Mutex

fun selectOnUnlock() {
    // Initialize mutexes as locked
    val mutex0 = Mutex(true)
    val mutex1 = Mutex(true)
    val mutex2 = Mutex(true)

    runBlocking() {
        launch {
            repeat(3) {
                val selected =
                    select<String> {
                        mutex0.onLock { "mutex0" }
                        mutex1.onLock { "mutex1" }
                        mutex2.onLock { "mutex2" }
                    }
                println("Selected: $selected")
            }
        }

        println("Unlocking: mutex2")
        mutex2.unlock()

        delay(100)
        println("Unlocking: mutex1")
        mutex1.unlock()

        delay(100)
        println("Unlocking: mutex0")
        mutex0.unlock()
    }
}

fun selectOnLock() {
    // Initialize mutexes as unlocked
    val mutex0 = Mutex(false)
    val mutex1 = Mutex(false)
    val mutex2 = Mutex(false)

    runBlocking() {
        launch {
            repeat(3) {
                val selected =
                    select<String> {
                        mutex0.onLock { "mutex0" }
                        mutex1.onLock { "mutex1" }
                        mutex2.onLock { "mutex2" }
                    }
                println("Selected: $selected")
            }
        }


        println("Locking: mutex2")
        mutex2.lock()

        delay(100)
        println("Locking: mutex1")
        mutex1.lock()

        delay(100)
        println("Locking: mutex0")
        mutex0.lock()
    }
}

fun main() {
    // I would not expect this to work
    println("Calling selectOnUnlock()")
    selectOnUnlock()

    //I would expect this to work
    println("\nCalling selectOnLock()")
    selectOnLock()
}

/* 
Output is:

Calling selectOnUnlock()
Unlocking: mutex2
Selected: mutex2
Unlocking: mutex1
Selected: mutex1
Unlocking: mutex0
Selected: mutex0

Calling selectOnLock()
Locking: mutex2
Selected: mutex0
Selected: mutex1
Locking: mutex1

*/