async with completion

DispatchQueueUtil.swift

extension DispatchQueue {
    public func async(execute work: @escaping () -> Void, complete: @escaping () -> Void) {
        async(execute: [work], complete: complete)
    }
    
    public func async(execute works: [() -> Void], complete: @escaping () -> Void) {
        let dispatchGroup = DispatchGroup()
        works.forEach { work in
            async(group: dispatchGroup) {
                work()
            }
        }
        dispatchGroup.notify(queue: .main) {
            complete()
        }
    }
}

DispatchQueueUtilUsage.swift

// main 에서 작업 후, main에서 completion
DispatchQueue.main.async(execute: {
    print("main single task")
}, complete: {
    print("main single task done")
})

// background 에서 작업 후, main에서 completion
DispatchQueue.global(qos: .background).async(execute: {
    print("background single task")
}, complete: {
    print("background single task done")
})

// main 에서 모든 작업 실행 후, main에서 completion
DispatchQueue.main.async(execute:
    [
        {
            print("main task 1")
        },{
            print("main task 2")
        },{
            print("main task 3")
        }
    ], complete: {
        print("main task done")
})

// background 에서 모든 작업 실행 후, main에서 completion
DispatchQueue.global(qos: .background).async(execute:
    [
        {
            print("background task 1")
        },{
            print("background task 2")
        },{
            print("background task 3")
        }
    ], complete: {
        print("background task done")
})