> On Feb 6, 2017, at 12:19 PM, Michael Gottesman via swift-dev > <swift-dev@swift.org> wrote: > > >> On Feb 6, 2017, at 11:44 AM, Jordan Rose <jordan_r...@apple.com >> <mailto:jordan_r...@apple.com>> wrote: >> >> >>> On Feb 6, 2017, at 11:25, Joe Groff via swift-dev <swift-dev@swift.org >>> <mailto:swift-dev@swift.org>> wrote: >>> >>> >>>> On Feb 6, 2017, at 11:22 AM, Michael Gottesman <mgottes...@apple.com >>>> <mailto:mgottes...@apple.com>> wrote: >>>> >>>> Here is my suggestion: >>>> >>>> 1. We assume by default the leaking case. >>>> 2. We change noreturn functions from C to maybe have a special semantic >>>> tag on them that says that cleanups should occur before them (i.e. >>>> UIApplicationMain). >> >> I'm not sure what you mean by this. Functions from C exist in both groups, >> and I don't see why one assumption is better than the other. >> >> >>> >>> I feel that "clean up before" is the safer ground case, and if we do any >>> work to whitelist a group, it should be for the common "leakable" >>> noreturns, like exit/_exit/abort/fatalError. That way, we momentarily burn >>> some pointless cycles in the case we get it "wrong" rather than permanently >>> leak memory. >> >> I don't like this because of the reverse issue: under -Onone, you may want >> to pop back up the stack in the debugger and see what values you had, and >> they won't be available. It's almost always possible to get things released >> sooner; usually more awkward to get them to stay alive. > > On the other hand, this is safe to do in the short term. We can special case > asserts. One thing to consider though is if this should be provided to users. > If not, we can just use semantics. Otherwise, we would need to discuss how to > surface this at the language level. > > Michael
Sorry I didn't jump in yesterday. I'm afraid I don't follow most of the reasoning expressed in the thread. I do completely understand Jordan's points. 'noreturn' functions are called from may-return functions. Guaranteeing cleanup would result in inconsistent behavior as a result of optimization. The optimizer can always shorten lifetimes when it determines that the caller can't access the object. But I don't see what that has to do with 'noreturn'. I agree that we *could* add a special "cleanup before" semantic tag for some C functions, but I'm not aware of a need to do that and there are definite drawbacks. -Andy
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