On 22 Aug 2018, at 21:42, Saagar Jha <saa...@saagarjha.com> wrote:
> 
>> Are they? kqueue() supports monitoring of fds, Mach ports and timers, so 
>> there’s really no reason that CFRunLoop would have to spawn a background 
>> thread just to monitor some file descriptors. As far as I can tell, the 
>> current CFRunLoop implementation is built on top of GCD, which sadly we 
>> don’t have the source code for
> 
> libdispatch is open source: 
> https://github.com/apple/swift-corelibs-libdispatch 
> <https://github.com/apple/swift-corelibs-libdispatch>

On 23 Aug 2018, at 04:30, Uli Kusterer <witness.of.teacht...@gmx.net> wrote:
> 
> 
> I recall hearing from someone at Apple that they basically ported GCD to 
> Linux for the Swift Linux release ... have you looked whether that code might 
> give any clues about what may be happening on macOS?


Interesting. That isn’t quite the same libdispatch that’s used on the macOS by 
the look of things, but it does appear to have things merged across from the 
macOS version. It looks, from a cursory examination, as if the macOS 
functionality is built on top of a kernel “work queue” implementation that 
lives inside the non-open-source pthread.kext. (I’m sure I’m not the only one 
to have noticed that quite a bit of functionality has been moved from open 
source parts of the macOS to closed-source libraries and KEXTs; personally I 
find this a disappointing development, as it makes debugging and developing 
software harder if it’s impossible to inspect the source code.)

Anyway, from what I can see it seems highly unlikely that there will be any 
background threads to monitor file descriptors, at least on the macOS.

Kind regards,

Alastair.

--
http://alastairs-place.net

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