> On Nov 4, 2016, at 9:12 AM, Johannes Weiß <johanneswe...@apple.com> wrote: > > Hi Joe, > >>> I just realised, that the problem is slightly worse than I originally >>> described. I believed that successful calls in between the actual call the >>> programmer wanted to make and capturing `errno` are not a problem. >>> >>> But POSIX seems to suggest [4] that "The setting of errno after a >>> successful call to a function is unspecified unless the description of that >>> function specifies that errno shall not be modified." . The Linux man page >>> [5] also mentions that "a function that succeeds is allowed to change >>> errno." >>> >>> To me this means that the issue is wider than just ARC. I think the problem >>> extends to memory allocations on the heap. Failed memory allocations aren't >>> a problem because they are terminal in Swift. However, _successful_ memory >>> allocations might be a problem because the malloc(3) that the Swift >>> compiler will use is absolutely free to set errno to 0 (or any other value >>> in fact) indicating success. (Said that at least malloc doesn't change >>> `errno` on the macOS or Linux I tested today, we probably shouldn't rely on >>> that though.) >>> >>> This makes it even more unpredictable to the programmer what a use of >>> `errno` in Swift will return. IMHO it shouldn't be exported to Swift as its >>> value is undefined almost(?) everywhere. >>> >>> [4]: http://pubs.opengroup.org/onlinepubs/9699919799/functions/errno.html >>> [5]: http://man7.org/linux/man-pages/man3/errno.3.html >> >> Swift's implicit allocations don't directly use malloc/free. > > Ah right, that's good to know. But still, "explicit" allocation by creating > an object does, right? > > Like > > class Foo {} > let x = Foo() > > does allocate through _swift_allocObject_ -> swift_slowAlloc -> malloc .
swift_slowAlloc does not need to be implemented by calling malloc. -Joe _______________________________________________ swift-evolution mailing list swift-evolution@swift.org https://lists.swift.org/mailman/listinfo/swift-evolution
