Concurrency-RaceCondition.swift

import Foundation

// Concurrent queue

// When the order of execution of tasks doesn't matter, you can use concurrent queue.
// Concurrent queue are faster than serial queue.
// Concurrent queue can create race conditions in the code.
// NSLock - Used to avoid the race condition.

var balance = 5000

let lock = NSLock()

struct Bank {
    let withdrawType: String
    
    func withdraw(amount: Int) {
        lock.lock()
        if balance > amount {
            print("\(withdrawType) : - Sufficient balance proceed with transcation!!!")
            
            Thread.sleep(forTimeInterval: Double.random(in: 0...4))
            
            balance = balance - amount
            
            print("\(withdrawType): - \(amount) Rs withdrawn from your account")
            print("\(withdrawType): - Current balance \(balance) Rs")
        } else {
            print("\(withdrawType): -  You have insufficient balance in your account")
        }
        
        lock.unlock()
    }
}

let queue = DispatchQueue(label: "concurrentQueue", attributes: .concurrent)

queue.async {
    let bank = Bank(withdrawType: "ATM")
    bank.withdraw(amount: 3000)
}

queue.async {
    let bank = Bank(withdrawType: "UPI")
    bank.withdraw(amount: 4000)
}