SomeHeavyOperationTasks

SomeHeavyOperationTasks.swift

import Foundation

func printWithThreadInfo(tag: String) {
    print("Thread \(Thread.current) - \(tag) - \(Thread.isMainThread)")
}

class SomeHeavyOperationTasks {
    
    func someHeavySynchronousTask() -> [Int] {
        var number: [Int] = []
        for i in 1...1000 {
            number.append(i)
        }
        
        printWithThreadInfo(tag: "someHeavySynchronousTask")
        return number
    }
    
    func someHeavyAsynchronousCallBackTask(_ completionHandler: ([Int]) -> Void) {
        
        printWithThreadInfo(tag: "someHeavyAsynchronousCallBackTask - Start")
        DispatchQueue.global(qos: .userInitiated).async {
            printWithThreadInfo(tag: "someHeavyAsynchronousCallBackTask - inside DispatchQueue.global")
            var number: [Int] = []
            for i in 1...1000 {
                number.append(i)
            }
        }
        printWithThreadInfo(tag: "someHeavyAsynchronousCallBackTask - after DispatchQueue.global")
        
        
    }
    // 1 Defined a heavy task asynchronous function with `async`
    func someHeavyAsynchronousConcurrencyTask(start:Int, end: Int) async -> [Int] {
        
        printWithThreadInfo(tag: "someHeavyAsynchronousConcurrencyTask - Start from \(start)")
        // 2 create a task to start the heavy operation. Using await here creats a suspension point where the control of thread is passed back to OS to perform some other important task. While our function is waiting for Task to get complete.
        let number = await Task { () -> [Int] in
            printWithThreadInfo(tag: "someHeavyAsynchronousConcurrencyTask - inside Task start from \(start)")
            var number: [Int] = []
            for i in start...end {
                number.append(i)
            }
            printWithThreadInfo(tag: "someHeavyAsynchronousConcurrencyTask - inside Task before return - \(start)")
            
            return number
        }.value
        // 3 Once Task is complete, suspension is revoked and it is to notice that OS may resume on any other arbitary thread not just the thread which starts the task.
        printWithThreadInfo(tag: "someHeavyAsynchronousConcurrencyTask - after await \(start)")
        return  number
    }
    
}