[swift-corelibs-dev] libdispatch/GCD for Swift 3.0 on Linux

David P Grove groved at us.ibm.com
Sun Jun 26 18:52:34 CDT 2016


	I've been making some progress on the Swift 3 overlay for dispatch on
a branch [1].  It builds, but doesn't do much more beyond that yet.  I
expect to raise a pull request within a week (once basic programs are


From:	Joseph Bell <joe at iachieved.it>
To:	David P Grove/Watson/IBM at IBMUS, Chris Bailey
            <BAILEYC at uk.ibm.com>
Cc:	swift-corelibs-dev at swift.org
Date:	06/26/2016 05:30 PM
Subject:	Re: [swift-corelibs-dev] libdispatch/GCD for Swift 3.0 on Linux

David, Chris,

Thanks again for the responses regarding libdispatch (GCD) on Linux with
Swift 3.0.  I took a stab at building what was there and indeed, I see
there are missing components to the overlay.  For example, I see where
Dispatch.swift contains things like "public extension DispatchGroup" but
there is no actual DispatchGroup defined anywhere (just extensions to it).
The same goes for DispatchSemaphore, DispatchQueue, DispatchWorkItem, etc.
Unless I am offbase and that is defined (I certainly couldn't find it).

At any rate, thanks again for the work you're doing bringing GCD to Linux;
I'm looking forward to it.


On Tue, Jun 21, 2016 at 10:24 AM, David P Grove <groved at us.ibm.com> wrote:
  Joseph Bell <joe at iachieved.it> wrote on 06/21/2016 09:15:00 AM:

  > Thanks for the details, I appreciate it.  I have seen the term
  > "Swift overlay" used, particularly in the context of libdispatch.
  > What does that mean exactly in this regard (searching for it returns
  > tutorials on overlay UIViews which I doubt is appropriate here).


  There's a layer of Swift code that sits on top of the non-Swift
  implementation of libdispatch to provide the Swift-level API for the
  library.  This is called the overlay.

  In Swift 2, the overlay for libdispatch was relatively thin.  In Swift 3
  it became thicker and on Darwin platforms more reliant on compiler
  support for importing Objective-C API declarations in a "Swifty" way.
  The main work item for getting the libdispatch Swift 3 APIs on Linux is
  to compensate for the lack of Objective-C by manually writing a layer (in
  Swift) that sits between the basic C-level APIs libdispatch provides on
  Linux and the desired user-visible Swift-3 APIs.


Joseph Bell

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