Serial Queue vs Concurrent with barrier tasks

[marcusway]

I've found PromiseKit enormously useful to use, and, as a relative noob in iOS, I've learned a lot by just poking around the source. So thanks to all contributors!

I was looking at the implementation of when here, and I was wondering: is using a concurrent DispatchQueue and then submitting only .barrier tasks to it any different from submitting tasks to a serial queue? In other words, would this code behave differently if barrier were a serial queue (and you didn't pass the .barrier flag to the sync call?

...

let barrier = DispatchQueue(label: "org.promisekit.barrier.when", attributes: .concurrent)

for promise in thenables {
    promise.pipe { result in
        barrier.sync(flags: .barrier) {
             // do stuff
        }
    }
}

[mxcl]

If we aren’t reading from it (looks like yeah) then probably it is behaving the same as a serial queue, yes. Haven't checked the code though.