DispatchWorkItem barrier attribute

gistfile1.txt

so this works as expected:

let conq = DispatchQueue(label: "ok", qos: .background, attributes: .concurrent   )
       // let conq = DispatchQueue.global(qos: .userInitiated)
        
        let dw1 = DispatchWorkItem {
            //sleep(2)
            print("dw1")
        }
        
        
        let dw2 = DispatchWorkItem {
            //sleep(2)
            print("dw2")
        }
        
        
        let dw3 = DispatchWorkItem {
            //sleep(2)
            print("dw3")
        }
        
        let dwbarrier = DispatchWorkItem(flags: .barrier) {
            
            print("barrier")
        }
        
        let dw4 = DispatchWorkItem {
            
            print("dw4")
        }
        
        
        let dw5 = DispatchWorkItem {
            
            print("dw5")
        }
        
        
        let dw6 = DispatchWorkItem {
            
            print("dw6")
        }
        
        conq.suspend()
        conq.async(execute: dw1)
        conq.async(execute: dw2)
        conq.async(execute: dw3)
        conq.async(execute: dwbarrier)
        conq.async(execute: dw4)
        conq.async(execute: dw5)
        conq.async(execute: dw6)
        conq.resume()
 
    }
    
producing:

dw2
dw1
dw3
barrier
dw4
dw5
dw6

BUT if you change to the global concurrent queue
let conq = DispatchQueue.global(qos: .background)

producing:

dw6
barrier
dw5
dw4
dw2
dw3
dw1

barrier no longer works

this may be 'as designed' but should be so noted.