GCD Async / Sync / Serial / Concurrent

gcd.swift

func doLongAsyncTaskInSerialQueue() {
    
    let serialQueue = DispatchQueue(label: "com.queue.Serial")
    for i in 1...5 {
        serialQueue.async {
            
            if Thread.isMainThread{
                print("task running in main thread")
            }else{
                print("task running in background thread")
            }
            let imgURL = URL(string: "https://upload.wikimedia.org/wikipedia/commons/0/07/Huge_ball_at_Vilnius_center.jpg")!
            let _ = try! Data(contentsOf: imgURL)
            print("\(i) completed downloading")
        }
    }
}



func doLongSyncTaskInSerialQueue() {
    let serialQueue = DispatchQueue(label: "com.queue.Serial")
    for i in 1...5 {
        serialQueue.sync {
            if Thread.isMainThread{
                print("task running in main thread")
            }else{
                print("task running in background thread")
            }
            let imgURL = URL(string: "https://upload.wikimedia.org/wikipedia/commons/0/07/Huge_ball_at_Vilnius_center.jpg")!
            let _ = try! Data(contentsOf: imgURL)
            print("\(i) completed downloading")
        }
    }
}

func doLongASyncTaskInConcurrentQueue() {
    let concurrentQueue = DispatchQueue(label: "com.queue.Concurrent", attributes: .concurrent)
    for i in 1...5 {
        concurrentQueue.async {
            if Thread.isMainThread{
                print("task running in main thread")
            }else{
                print("task running in background thread")
            }
            let imgURL = URL(string: "https://upload.wikimedia.org/wikipedia/commons/0/07/Huge_ball_at_Vilnius_center.jpg")!
            let _ = try! Data(contentsOf: imgURL)
            print("\(i) completed downloading")
        }
        print("\(i) executing")
    }
}

func doMultipleSyncTaskWithinAsynchronousOperation() {
    let concurrentQueue = DispatchQueue(label: "com.queue.Concurrent", attributes: .concurrent)
    concurrentQueue.async {
        let concurrentQueue = DispatchQueue.global(qos: DispatchQoS.QoSClass.default)
        for i in 1...5 {
            concurrentQueue.sync {
                let imgURL = URL(string: "https://upload.wikimedia.org/wikipedia/commons/0/07/Huge_ball_at_Vilnius_center.jpg")!
                let _ = try! Data(contentsOf: imgURL)
                print("\(i) completed downloading")
            }
            print("\(i) executed")
        }
    }
}

doLongAsyncTaskInSerialQueue()
doLongASyncTaskInConcurrentQueue()


DispatchQueue.global(qos: .background).async {
    // Do some background work
    DispatchQueue.main.async {
        // Update the UI to indicate the work has been completed
    }
}

DispatchQueue.global(qos: .utility).sync {
    // Background Task
    DispatchQueue.main.sync {
        // App will crash
    }
}

let customSerialQueue = DispatchQueue(label: "com.yogevsitton.MyApp.myCustomSerialQueue")

customSerialQueue.sync {
    // Synchronous code
    customSerialQueue.sync {
        // This code will never be executed and the app is now in deadlock
    }
}

DispatchQueue.global(qos: .utility).async {
    // Asynchronous code running on the low priority queue
}

DispatchQueue.main.async {
    // Asynchronous code running on the main queue
}

DispatchQueue.global(qos: .userInitiated).sync {
    // Synchronous code running on the high prioriy queue
}

doMultipleSyncTaskWithinAsynchronousOperation()