[swift-evolution] [Concurrency] async/await + actors

Thomas tclementdev at free.fr
Fri Aug 18 14:23:31 CDT 2017

> On 18 Aug 2017, at 20:57, Chris Lattner <clattner at nondot.org> wrote:
>> I'm a bit worried about the mention of dispatch_sync() here (although it may just be there to illustrate the deadlock possibility). I know the actor runtime implementation is not yet defined, but just wanted to mention that dispatch_sync() will lead to problems such as this annoying thing called thread explosion. This is why we currently cannot use properties in our code (getters would require us to call dispatch_sync() and we want to avoid that), instead we are writing custom async getters/setters with callback blocks. Having async property getters would be pretty awesome.
> I think that awaiting on the result of an actor method ends up being pretty similar (in terms of implementation and design tradeoffs) as dispatch_sync.  That said, my understanding is that thread explosion in GCD happens whenever something blocks a GCD thread, not when it politely yields control back to GCD.  Am I misunderstanding what you mean.

disptach_sync() calls will cause the GCD thread to block (waiting for the queue to be available). I'm pretty sure this causes libdispatch to spawn more threads if needed (for example if dispatch_async() calls are made in other parts of the program), up to thread explosion.


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