Demonstration of write lock with upgrade in Kotlin

lockWithUpgradeExample.kt

import java.util.concurrent.locks.ReentrantReadWriteLock
import kotlin.concurrent.read
import kotlin.concurrent.write

fun lockWithoutUpgrade() {
    val lock = ReentrantReadWriteLock()

    println("Acquire read lock")
    lock.readLock().lock()
        println("Inside read lock")
    
        println("Acquire write lock")
        lock.writeLock().lock()
            println("Inside write lock")
            lock.writeLock().unlock()    
        println("Released write lock")
    
        lock.readLock().unlock()
    println("Released read lock")
}

fun lockWithUpgrade() {
    val lock = ReentrantReadWriteLock()

    println("Acquire read lock")
    lock.read {
        println("Inside read lock")

        println("Acquire write lock")
        lock.write {
            println("Inside write lock")
        }

        println("Released write lock")
    }

    println("Released read lock")
}

fun main(args: Array<String>) {
    lockWithUpgrade()
}