Philosophers problem solved with semaphores on swift

philosophers.swift

import UIKit

class Semaphore {
    var n: Int
    
    init(n: Int) {
        self.n = n
    }
    
    func P() {
        while self.n == 0 {}
        self.n = self.n - 1
    }
    
    func V() {
        self.n = self.n + 1
    }
}

var table = Semaphore(n: 4)
var chopsticks: [Semaphore] = []
var ran = 0

for _ in 1...5 {
    chopsticks.append(Semaphore(n: 1))
}

func philosopher(n: Int) {
    while ran < 50 {
        table.P()
        chopsticks[n].P()
        chopsticks[n+1 % 5].P()
        print("Philosopher #\(n+1) is eating :P")
        ran = ran + 1
        chopsticks[n].V()
        chopsticks[n+1 % 5].V()
        table.V()
    }
}

for i in 0...4 {
    DispatchQueue.global(qos: .userInitiated).async {
        philosopher(n: i)
    }
}