[libdispatch-dev] Queue size

Thomas Clement tclementdev at gmail.com
Thu Oct 7 07:57:06 PDT 2010

On Oct 7, 2010, at 3:10 PM, Dave Zarzycki wrote:

> On Oct 7, 2010, at 8:35 AM, Thomas Clement wrote:
>>> Queues cannot have variable widths - it's either 1 or "infinite".  That idea was considered but ultimately dropped given that it only made submitting things to queues even less deterministic in terms of where/how they would run, and there is already a way (again, semaphores) to get that behavior, so this would have only added complexity to all queues for little overall gain.
>> I'm confused. What about the dispatch_queue_set_width() private function?
>> Isn't this already implemented and functional?
> "Implemented and functional" is not the bar we use for making an API publicly available. It also has to be sustainable and supportable.
> Unfortunately, dispatch_queue_set_width() fails at the latter goals. That API encourages bad design, and practically speaking, it was only created so that developers can workaround underlying bugs (latent serialization). We'd much rather see developers fix (or file bugs) against the underlying problems than see a hierarchy of long term bandaids and workarounds be created.

I understand.
The problem I'm facing is that some of my dispatched code at some point pauses its execution (basically locking on pthread_cond_wait() or similar) and libdispatch spawns way too many threads as a result (hundreds of them).

It is difficult if not impossible to remove these locks. I guess the solution is to limit the number of dispatched blocks on my queues using dispatch semaphores.


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