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When will a deallocation occur? When release is called and the referece count is zero. This is deterministic, unlike GC which will perform the deallocation when

When will a deallocation occur? When release is called and the referece count is zero. This is deterministic, unlike GC which will perform the deallocation when it feels like it. I think you've confused determinism with regards to a program and the inputs to that program. Any retain/release program is deterministic because it always behaves in the same manner. Given any possible input I can tell you exactly when and on which lines of code the deallocations will occur. You can't know that with GC, especially when other libraries and threads enter the equation. Which deallocations occur and in which order depend on the input to the program, but we still know in advance all possible lines of code where specific deallocations can occur and we have complete control over that. With GC we wouldn't know that and we couldn't control it. Knowing when deallocations can occur and having control over that is the reason to choose ARC over GC in the first place. Not the other way around. With respect to manual retain/release, ARC doesn't take anything away: I can still retain an extra count of a large object to prevent its untimely release and share that object via ARC at the same time.

Skinney 12y ago
Two things. First, most GC doesn't actually deallocate anything, but that's a minor nitpick. The second, more important note, is that you are now describing a system where everything is garbage collected. This needn't be the case. In a language like Go, you have control over what get's stack allocated and what is placed in a GC. When that choice can be made, then you really can tell when given objects are deallocated. Of course, since the stack is a fixed size construct, I guess you don't really deallocate these things either... It's also worth noting that GCs rarely does anything because it feels like it, but because you are allocating past a certain limit. Knowing the size of objects, and given that the allocator can provide you with the current size of allocated objects, you should be able to determine if a GC is likely to incur in the next lines of code. This determination becomes harder when threads enter the picture, unless you're using a GC scheme like Erlang, which have one GC per process (lightweight thread). Some GCs also allow you to pause and resume them, for when you really want to avoid GC cycles, this can of course lead your program to crash if you allocate past your limit. As always in computer science, 'it depends'.

Skinney 12y ago

Two things. First, most GC doesn't actually deallocate anything, but that's a minor nitpick. The second, more important note, is that you are now describing a system where everything is garbage collected. This needn't be the case. In a language like Go, you have control over what get's stack allocated and what is placed in a GC. When that choice can be made, then you really can tell when given objects are deallocated. Of course, since the stack is a fixed size construct, I guess you don't really deallocate these things either... It's also worth noting that GCs rarely does anything because it feels like it, but because you are allocating past a certain limit. Knowing the size of objects, and given that the allocator can provide you with the current size of allocated objects, you should be able to determine if a GC is likely to incur in the next lines of code. This determination becomes harder when threads enter the picture, unless you're using a GC scheme like Erlang, which have one GC per process (lightweight thread). Some GCs also allow you to pause and resume them, for when you really want to avoid GC cycles, this can of course lead your program to crash if you allocate past your limit. As always in computer science, 'it depends'.