4 ms·

Now I'm curious, what is the difference between automated ref counting and "vanilla" ref counting? And of these two, where does the C++ shared pointer fit?

skohan 7y ago
ARC as in "Atomic Reference Counting". ARC uses atomic operations to increment and decrement reference counts. That means these operations must be synchronized between threads. synchronization between threads/cores tends to be an expensive operation. This is required for reference counting objects between threads. Otherwise, you might have one thread try to release an object at the same time another thread is trying to increment the reference count. It's just overkill for objects which are only ever referenced from a single thread.
- hellofunk 7y ago
  Well that is confusing. Any Apple developer has known for many years that ARC means Automatic Reference Counting: https://docs.swift.org/swift-book/LanguageGuide/AutomaticReferenceCounting.html https://docs.swift.org/swift-book/LanguageGuide/AutomaticRef... I never heard this alternate and very different expansion for that term.
  - skohan 7y ago
    It's an overloaded acronym to be sure. Atomic reference counting is a familiar concept in systems programming languages like C++ and Rust. It just so happens that Apple's automatic reference counting is also atomic.
  - MaulingMonkey 7y ago
    It's a bit less confusing in practice - the full types are std::rc::Rc and std::sync::Arc (where std::sync is all multithreading stuff, and you have to actually use that name to get access to Arc in your code), and both are well documented (including spelling out the acronym): https://doc.rust-lang.org/std/rc/struct.Rc.html https://doc.rust-lang.org/std/rc/struct.Rc.html https://doc.rust-lang.org/std/sync/struct.Arc.html https://doc.rust-lang.org/std/sync/struct.Arc.html ...I could see this causing merry hell if trying to do advance interop between Swift and Rust, though, and it's admittedly probably going to be a minor stumbling block for Apple-first devs. (I managed to avoid confusion, but I just port to Apple targets, they're not my bread and butter.)

skohan 7y ago

ARC as in "Atomic Reference Counting". ARC uses atomic operations to increment and decrement reference counts. That means these operations must be synchronized between threads. synchronization between threads/cores tends to be an expensive operation. This is required for reference counting objects between threads. Otherwise, you might have one thread try to release an object at the same time another thread is trying to increment the reference count. It's just overkill for objects which are only ever referenced from a single thread.

hellofunk 7y ago
Well that is confusing. Any Apple developer has known for many years that ARC means Automatic Reference Counting: https://docs.swift.org/swift-book/LanguageGuide/AutomaticReferenceCounting.html https://docs.swift.org/swift-book/LanguageGuide/AutomaticRef... I never heard this alternate and very different expansion for that term.
- skohan 7y ago
  It's an overloaded acronym to be sure. Atomic reference counting is a familiar concept in systems programming languages like C++ and Rust. It just so happens that Apple's automatic reference counting is also atomic.
- MaulingMonkey 7y ago
  It's a bit less confusing in practice - the full types are std::rc::Rc and std::sync::Arc (where std::sync is all multithreading stuff, and you have to actually use that name to get access to Arc in your code), and both are well documented (including spelling out the acronym): https://doc.rust-lang.org/std/rc/struct.Rc.html https://doc.rust-lang.org/std/rc/struct.Rc.html https://doc.rust-lang.org/std/sync/struct.Arc.html https://doc.rust-lang.org/std/sync/struct.Arc.html ...I could see this causing merry hell if trying to do advance interop between Swift and Rust, though, and it's admittedly probably going to be a minor stumbling block for Apple-first devs. (I managed to avoid confusion, but I just port to Apple targets, they're not my bread and butter.)