DispatchSemaphore.swift

import Foundation

// Create a custom concurrent queue
let concurrentQueue = DispatchQueue(label: "com.example.concurrentQueue", attributes:.concurrent)

var sharedArray: [Int] = []


let numberOfThreadsAllowedToAccessSharedReource: Int = 1
// Semaphore to control access the shared resource
let semaphore = DispatchSemaphore(value: numberOfThreadsAllowedToAccessSharedReource)

// Function to write to the shared array in a thread-safe manner using semaphore
func writeToArray(element: Int) {
    semaphore.wait()
    defer {
        semaphore.signal()
    }
    
    concurrentQueue.async {
        sharedArray.append(element)
        print("Added \(element) to array")
    }
}

func readFromArray() {
    semaphore.wait()
    defer {
        semaphore.signal()
    }
    concurrentQueue.sync {
        print("Array contents: \(sharedArray)")
    }
}

// Perform write operations using dispatch semaphore
writeToArray(element: 1)
writeToArray(element: 2)
writeToArray(element: 3)

// Perform read operations sequentially
readFromArray()
readFromArray()

// Perform another write operation with semaphore
writeToArray(element: 4)

// Perform read operations again
readFromArray()