Simple dispatch_group and dispatch_semaphore sample

gistfile1.swift

//: Playground - noun: a place where people can play

import Foundation

// DispatchGroup sample.
// we are waiting for all async blocks to be finished before typing "[Dispatch Group] sample has finished"
let group = DispatchGroup()

let q1 = DispatchQueue.global(qos: .background)
let q2 = DispatchQueue.global(qos: .background)
let q3 = DispatchQueue.global(qos: .background)

q1.async(group: group) { () -> Void in
    sleep(1)
    print("[Dispatch Group] Hello I am here1")
}

q2.async(group: group) { () -> Void in
    sleep(2)
    print("[Dispatch Group] Hello I am here2")
}

q3.async(group: group) { () -> Void in
    sleep(3)
    print("[Dispatch Group] Hello I am here3")
}

group.wait()

print("[Dispatch Group] sample has finished.")


// dispatch_semaphore sample.
// we are waiting for all async blocks to be finished before typing "[Dispatch Semaphore] sample has finished"
// Slightly cumbersome than dispatch_group_async b/c you 'have to' call _wait method for the number of resources.
// But it is also beneficial because you can start waiting for number of resources even before async block has started.
let semaphore = DispatchSemaphore(value: 0)

q1.async { () -> Void in
    sleep(1)
    print("[Dispatch Semaphore] Hello I am here1")
    semaphore.signal()
}

q2.async { () -> Void in
    sleep(2)
    print("[Dispatch Semaphore] Hello I am here2")
    semaphore.signal()
}

q3.async { () -> Void in
    sleep(3)
    print("[Dispatch Semaphore] Hello I am here3")
    semaphore.signal()
}

semaphore.wait()
semaphore.wait()
semaphore.wait()

print("[Dispatch Semaphore] sample has finished.")