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Both ARC and garbage collection are memory management techniques. ARC does not equal garbage collection though. Garbage collection runs at intervals and is trig

Both ARC and garbage collection are memory management techniques. ARC does not equal garbage collection though. Garbage collection runs at intervals and is triggered by certain signals (memory pressure, etc), pauses all threads and scans for objects that can be deallocated. It is a very different concept than ARC.

twoodfin 2y ago
https://courses.cs.washington.edu/courses/cse590p/05au/p50-bacon.pdf https://courses.cs.washington.edu/courses/cse590p/05au/p50-b... This paper makes a strong argument that “pure” tracing garbage collection and “rote” reference counting are effectively duals at the opposite ends of a spectrum of implementation choices. For example, GC’s often optimize differently for young vs. old objects. How do they distinguish these? By “counting” (one bit) their references across one or more traces in a series of sweeps.
- 01HNNWZ0MV43FF 2y ago
  And a hot wheels car is a car, but I would be perplexed to see one offered to me at a car dealership
Tuna-Fish 2y ago
ARC is a method of implementing garbage collection, and is discussed as such in academic literature. What you are equating with "garbage collection" is Mark-Sweep, which is an another way to implement GC, with a very different set of tradeoffs. (Broadly, better throughput at the expense of higher latency.)
- 7jjjjjjj 2y ago
  In common usage everyone understands that GC = tracing GC.
112233 2y ago
Deleting large hierarchy of objects when the last reference gets decremented also is triggered by a certain signal (reference decrement) and pauses all threads while it collects garbage. There are even tunable GC that become ARC if you set particular parameter to "N=1"
- pessimizer 2y ago
  > There are even tunable GC that become ARC if you set particular parameter to "N=1" You can call a pointer to a value a "one-element static array."
- zozbot234 2y ago
  I'm not sure that collecting a large hierarchy of objects requires pausing all threads. What can definitely require pausing threads (other than in specialized concurrent collectors) is the tracing step, which relies on some invariants that in simple GC implementations (not the more specialized concurrent ones mentioned earlier) are only ensured at very specific points in the program (known as GC "safepoints").
  - 112233 2y ago
    My bad, thanks for correcting! Of course single thread freeing a lot of heap allocations will not pause other threads by itsel. What I had to write was: calling destructor of an object that in turn calls destructors of other objects (because a large tree of reference counted objects loses last reference to it's root) stops that thread, until all deallocation is done.

twoodfin 2y ago

https://courses.cs.washington.edu/courses/cse590p/05au/p50-bacon.pdf https://courses.cs.washington.edu/courses/cse590p/05au/p50-b... This paper makes a strong argument that “pure” tracing garbage collection and “rote” reference counting are effectively duals at the opposite ends of a spectrum of implementation choices. For example, GC’s often optimize differently for young vs. old objects. How do they distinguish these? By “counting” (one bit) their references across one or more traces in a series of sweeps.

01HNNWZ0MV43FF 2y ago
And a hot wheels car is a car, but I would be perplexed to see one offered to me at a car dealership

Tuna-Fish 2y ago

ARC is a method of implementing garbage collection, and is discussed as such in academic literature. What you are equating with "garbage collection" is Mark-Sweep, which is an another way to implement GC, with a very different set of tradeoffs. (Broadly, better throughput at the expense of higher latency.)

7jjjjjjj 2y ago
In common usage everyone understands that GC = tracing GC.

112233 2y ago

Deleting large hierarchy of objects when the last reference gets decremented also is triggered by a certain signal (reference decrement) and pauses all threads while it collects garbage. There are even tunable GC that become ARC if you set particular parameter to "N=1"

pessimizer 2y ago
> There are even tunable GC that become ARC if you set particular parameter to "N=1" You can call a pointer to a value a "one-element static array."
zozbot234 2y ago
I'm not sure that collecting a large hierarchy of objects requires pausing all threads. What can definitely require pausing threads (other than in specialized concurrent collectors) is the tracing step, which relies on some invariants that in simple GC implementations (not the more specialized concurrent ones mentioned earlier) are only ensured at very specific points in the program (known as GC "safepoints").
- 112233 2y ago
  My bad, thanks for correcting! Of course single thread freeing a lot of heap allocations will not pause other threads by itsel. What I had to write was: calling destructor of an object that in turn calls destructors of other objects (because a large tree of reference counted objects loses last reference to it's root) stops that thread, until all deallocation is done.