Why does MCNearbyServiceAdvertiser use a dispatch queue internally?

Question

While I was browsing through the iOS 7 runtime headers, something caught my eye. In the MCNearbyServiceAdvertiser class, part of the Multipeer Connectivity framework, a property called syncQueue is and multiple methods prefixed with sync are defined. Some of the methods both exist in a prefixed and non-prefixed version, such as startAdvertisingPeer and syncStartAdvertisingPeer.

My question is, what would be the purpose of both this property and these prefixed methods, and how are they combined?

(edit: removed the remark that the queue is serial as pointed out by CouchDeveloper, since we cannot know this)

Answer 1

As you know, the implementation is private.

Having a dispatch queue whose name is syncQueue may not mean that this queue is a serial queue. It might be a concurrent queue as well.

We can only have a guess what the startAdvertisingPeer and the "prefixed" version syncStartAdvertisingPeer might mean.

For example, in order to fulfill internal prerequisites startAdvertisingPeer might assume that it is always invoked from an execution context except the syncQueue. That way, it can synchronously dispatch to the syncQueue with invoking syncStartAdvertisingPeer without ending up in a deadlock. On the other hand, syncStartAdvertisingPeer will always assume to execute on the syncQueue, that way guaranteeing concurrency.

But, as stated, we don't know the actual details - it's just a rough guess. Usually, you should read the documentation - and not some private header details to draw a picture in your mind how this class might likely work.