> On Mar 14, 2017, at 3:53 PM, Greg Parker via swift-dev <swift-dev@swift.org> > wrote: > >> >> On Mar 14, 2017, at 2:16 PM, John McCall <rjmcc...@apple.com> wrote: >> >>> On Mar 14, 2017, at 5:08 PM, Jordan Rose via swift-dev >>> <swift-dev@swift.org> wrote: >>> >>>> On Mar 14, 2017, at 13:52, Greg Parker via swift-dev <swift-dev@swift.org> >>>> wrote: >>>> >>>>> On Mar 14, 2017, at 1:34 PM, Greg Parker via swift-dev >>>>> <swift-dev@swift.org> wrote: >>>>> >>>>>> On Mar 14, 2017, at 12:43 PM, Joe Groff <jgr...@apple.com> wrote: >>>>>> >>>>>> Hey Greg, what are the correct refcounting bits now to set in a global >>>>>> statically-emitted heap object that shouldn't ever be released? >>>>> >>>>> For now use the same thing that stack-allocated objects use. I forget >>>>> what the bit pattern is exactly. (I assume you are not in strictly >>>>> read-only memory and can tolerate writes to the refcount word. We don't >>>>> yet have an implementation for immortal read-only objects.) >>>> >>>> Oh wait, you *don't* want to use what stack-allocated objects use. They >>>> get deinited without being deallocated, and I assume you want neither >>>> deinit nor dealloc. Let me work this out. >>> >>> Wouldn’t it be okay to just emit it with an unbalanced retain? >> >> It's better if there's some way to make an object completely ref-count >> inert. Often, the compiler only sees one side of a retain/release pair, >> like when you return a constant NSString — you know locally that you're >> retaining a constant string, but you're returning it to some context that >> has no idea what it's getting. If the object is just unbalanced-retained, >> you have to preserve the retain or else the caller might release it. >> (That's true even if the imbalance is quite large — no fair crashing the >> program but only after a function's been called 2^19 times! Imagine >> reproducing that...) Making the object completely inert means you can just >> unconditionally say "hey, I know R/R are no-ops on this value" and delete >> them as a peephole. > > That's right. Unbalanced retain is the solution today. I expect a truly inert > solution soon.
Cool. Do you think we'd be able to avoid atomic barriers on inert objects, or would that unfairly impact freeable objects? -Joe _______________________________________________ swift-dev mailing list swift-dev@swift.org https://lists.swift.org/mailman/listinfo/swift-dev
