GCD(Grand Central Patch)

Queue

Fist-in Fist-out

 

Dispatch Queue

1. Main Queue
   DispatchQueue.main.async{}
2. Global Queue
   Qos(Quality of Service)
   1> userInteractive - UI related
   2> userInitiated
   3> default
   4> utility - networking, read write
   5> background - download, position update
   DispatchQueue.globa(sos: .background).async {}
3. Custom Queue
   let concurrentQueue = DispatchQueue(label: “concurrent”, qos: .background, attributes: .concurrent)
   let serialQueue = DispatchQueue(label: “serial”, qos: .background)

 

Use 2 Queue simultaneously

DispatchQueue.global(qos: .background).async {

 let image = downloadImageFromServer()

 DispatchQueue.main.async {

  self.imageView.image = image

  }

}

 

Sync & Async

asynchronous

synchronous