Producer/Consumer model (without Conditional variable)

val mutex = java.util.concurrent.locks.ReentrantLock()

const val FULL = 2
var que = 0

fun prod() {
    while (true) {
        // P0: lock
        mutex.lock()
        // P1: test
        while (que == FULL) {
            // P4: wait-room
            mutex.unlock()
            // P5: retry
            mutex.lock()
        }
        // P2: produce
        que += 1
        // P3: free
        mutex.unlock()
    }
}

fun cons() {
    while (true) {
        // Q0: lock
        mutex.lock()
        // Q1: test
        while (que == 0) {
            // Q4: wait-message
            mutex.unlock()
            // Q5: retry
            mutex.lock()
        }
        // Q2: consume
        que -= 1
        // Q3: free
        mutex.unlock()
    }
}

This producer/consumer state transition diagram:

Queue size 1, Producer x 1, Consumer x 1:

Queue size 2, Producer x 1, Consumer x 1:

Queue size 2, Producer x 2, Consumer x 1:

Queue size 2, Producer x 1, Consumer x 2:

ryohji/prod-cons-1.md