Dispatch queue wakeup slow quality of service

Hi Apple,


I happened to encounter this crash today. It gave " dispatch_queue_wakeup_with_qos_slow ". Unfortunately, there is no information on this issue elsewhere on the internet. So what exactly does it mean by " slow quality of service " during the waking up of a thread in the dispatch queue?


Thanks!
Edwin

Replies

I suspect that you’re misreading this identifier. You should read it as “dispatch queue wakeup with QoS, taking the slow path”. Many algorithms within Dispatch have a fast path, which is the typical case when things go well (no lock contention and so on). Clearly the existence of a fast path implies that there also exists a slow path, and that’s what this routine implements.

If you want to see this in context you can look at the Dispatch source code for this routine.

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