4 ms·

> A GC must maintain the property that a leak is only possible if an object is reachable from a root. RC on its own does not obey this property. This is certai

by Kranar 5y ago

> A GC must maintain the property that a leak is only possible if an object is reachable from a root. RC on its own does not obey this property. This is certainly a false claim then. What you're describing is a precise garbage collector, but there also exist conservative garbage collectors which will fail to reclaim objects even when no cycle exists so long as any integer interpretation of currently allocated memory shares the same integer interpretation of an object's memory address. GNU Java, and the Mono implementation of .NET both use the Boehm conservative garbage collector and they are most certainly still considered garbage collected systems: https://en.wikipedia.org/wiki/Boehm_garbage_collector https://en.wikipedia.org/wiki/Boehm_garbage_collector

zarzavat 5y ago
This isn’t formal science. We are practitioners and so definitions have to be practical. If Boehm GCs really leak as much as you claim then nobody would use them. The issue with cycles is that it can easily lead to significant memory leaks if a large subgraph gets caught in a cycle. A definition of GC that excludes this capability does not have the contract of “You only have to worry about reachability from roots”.
- Kranar 5y ago
  >This isn’t formal science. Computer science is absolutely a formal science in every sense of the word. >If Boehm GCs really leak as much as you claim then nobody would use them. I mean if anything this argument applies more to your characterization that reference counting easily leads to memory exhaustion due to cycles than it does to conservative garbage collectors. If RC based garbage collectors leaked as much as your post implies then nobody would use them. And yet Swift, a language that is almost exclusively used with large graphs(that's how most UIs are represented in memory) and that exhibits all kinds of non-deterministic shared ownership uses RC based garbage collection. Objects involved in UI code are shared in wildly unpredictable ways with no clear hierarchy among layouts, event handlers, observables, IO systems, etc... >A definition of GC that excludes this capability does not have the contract of “You only have to worry about reachability from roots”. Exactly, because that's not part of the contract for a GC. That's part of the contract for a tracing garbage collector: https://en.wikipedia.org/wiki/Tracing_garbage_collection https://en.wikipedia.org/wiki/Tracing_garbage_collection When your definitions don't fit reality then it's time to adjust your definitions, not reality.

by Kranar 5y ago

zarzavat 5y ago

This isn’t formal science. We are practitioners and so definitions have to be practical. If Boehm GCs really leak as much as you claim then nobody would use them. The issue with cycles is that it can easily lead to significant memory leaks if a large subgraph gets caught in a cycle. A definition of GC that excludes this capability does not have the contract of “You only have to worry about reachability from roots”.

Kranar 5y ago
>This isn’t formal science. Computer science is absolutely a formal science in every sense of the word. >If Boehm GCs really leak as much as you claim then nobody would use them. I mean if anything this argument applies more to your characterization that reference counting easily leads to memory exhaustion due to cycles than it does to conservative garbage collectors. If RC based garbage collectors leaked as much as your post implies then nobody would use them. And yet Swift, a language that is almost exclusively used with large graphs(that's how most UIs are represented in memory) and that exhibits all kinds of non-deterministic shared ownership uses RC based garbage collection. Objects involved in UI code are shared in wildly unpredictable ways with no clear hierarchy among layouts, event handlers, observables, IO systems, etc... >A definition of GC that excludes this capability does not have the contract of “You only have to worry about reachability from roots”. Exactly, because that's not part of the contract for a GC. That's part of the contract for a tracing garbage collector: https://en.wikipedia.org/wiki/Tracing_garbage_collection https://en.wikipedia.org/wiki/Tracing_garbage_collection When your definitions don't fit reality then it's time to adjust your definitions, not reality.