4 ms·

Most go data is value types that can be assumed to be on the stack, unless you introduce a pointer explicitly or use one of the referenceish types like interfac

by bbatha 8y ago

Most go data is value types that can be assumed to be on the stack, unless you introduce a pointer explicitly or use one of the referenceish types like interface, string, array or map. Its very easy for both the programmer and the compiler to see when data escapes. Java on the other hand is pathologically bad for escape analysis, outside of ints and floats literally every object in java is presumed to be on the heap. Even C# has less heap pressure than java typically because of more value type options, and not type erasing greatly improves the JIT's escape analysis. After sufficient JITing Java may reach go level of garbage generation, it may not: but its not deterministic.

pjmlp 8y ago
Only if you are speaking about Hotspot. GraalVM and other Java JITs (J9, Azul, PTG, ...) have much better escape analysis algorithms.
mike_hearn 8y ago
That's garbled in several ways I'm afraid. Firstly type erasure and escape analysis are un-related. Whether an object escapes or not is unrelated to things like whether it's a List<Integer> or List<int>. Secondly .NET doesn't do escape analysis at all: https://github.com/dotnet/coreclr/issues/1784 https://github.com/dotnet/coreclr/issues/1784 Thirdly HotSpot will happily escape analyze and then scalar replace regular objects, it isn't limited to ints and floats. It can make a big difference in many situations. Fourthly and finally, if it were "easy to see where data escapes" in Go there wouldn't need to be tools to help the programmer find out, and Go developers wouldn't spend time manually tweaking to try and ensure the optimisation works.
- jules 8y ago
  Type erasure and escape analysis are not entirely unrelated. If you have an array of pairs and store a pair into that array then the pair is considered to escape in Java because you're actually storing a pointer to your original pair. In C# that array can store a true array of pairs rather than an array of pointers to pairs. A pair you store gets copied into the array, so the original pair does not have to be considered to escape and can be stored on the stack and deallocated when the function exits. Although C# does not have escape analysis, its value type vs reference type distinction serves roughly the same purpose, but under manual control of the programmer.

by bbatha 8y ago

pjmlp 8y ago

Only if you are speaking about Hotspot. GraalVM and other Java JITs (J9, Azul, PTG, ...) have much better escape analysis algorithms.

mike_hearn 8y ago

That's garbled in several ways I'm afraid. Firstly type erasure and escape analysis are un-related. Whether an object escapes or not is unrelated to things like whether it's a List<Integer> or List<int>. Secondly .NET doesn't do escape analysis at all: https://github.com/dotnet/coreclr/issues/1784 https://github.com/dotnet/coreclr/issues/1784 Thirdly HotSpot will happily escape analyze and then scalar replace regular objects, it isn't limited to ints and floats. It can make a big difference in many situations. Fourthly and finally, if it were "easy to see where data escapes" in Go there wouldn't need to be tools to help the programmer find out, and Go developers wouldn't spend time manually tweaking to try and ensure the optimisation works.

jules 8y ago
Type erasure and escape analysis are not entirely unrelated. If you have an array of pairs and store a pair into that array then the pair is considered to escape in Java because you're actually storing a pointer to your original pair. In C# that array can store a true array of pairs rather than an array of pointers to pairs. A pair you store gets copied into the array, so the original pair does not have to be considered to escape and can be stored on the stack and deallocated when the function exits. Although C# does not have escape analysis, its value type vs reference type distinction serves roughly the same purpose, but under manual control of the programmer.