Re: [OT] Sync vs ASync Server Comms
Re: [OT] Sync vs ASync Server Comms
- Subject: Re: [OT] Sync vs ASync Server Comms
- From: Kyle Sluder <email@hidden>
- Date: Mon, 25 Feb 2013 15:03:13 -0800
On Mon, Feb 25, 2013, at 02:45 PM, Steve Sisak wrote:
>
> The current trend is away from threads and toward asynchronous
> programming.
>
> That's orthogonal to whether your tasks are run on a single
> (XXRunLoop) or multiple (GCD) threads -- the advantage of GCD is that
> the system gets do decide how many worker threads to fire up based on
> the number of cores available, system load, and who's blocked.
They're orthogonal, but they don't compose well.
1. You cannot assume anything about the thread on which a block runs
after being submitted to a GCD queue (other than the main queue). So no
runloop-dependent technologies for you. That means you cannot call
asynchronous Cocoa APIs from an async queue.
2. Blocking queues is _extremely_ dangerous, to the point where you
mustn't do it. At best, you'll cause GCD to spin up extra worker threads
unnecessarily. At worst, you'll cause deadlock as you exhaust your
thread pool. This means you cannot call synchronous (blocking) Cocoa
APIs from an async queue.
Long story short: do not mix GCD queues and long-term communications
APIs.
--Kyle Sluder
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