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> Rust can also do arena allocations, Is there a language that can't? The author isn't saying it's literally impossible to batch allocate, just that the defau

by Mawr 11mo ago

> Rust can also do arena allocations, Is there a language that can't? The author isn't saying it's literally impossible to batch allocate, just that the default happy path of programming in Rust & Go tends to produce a lot of allocations. It's a take more nuanced than the binary possible vs impossible.

seanmcdirmid 11mo ago
Pretty hard to do arena allocation in Java without JVM primitive support.
- jeberle 11mo ago
  Not sure what you mean by "primitive support". Java 22 added FFM (Foreign Function & Memory). It works w/ both on-heap & off-heap memory. It has an Arena interface. https://openjdk.org/jeps/454 https://openjdk.org/jeps/454 https://docs.oracle.com/en/java/javase/25/docs/api/java.base/java/lang/foreign/Arena.html https://docs.oracle.com/en/java/javase/25/docs/api/java.base...
  - Dylan16807 11mo ago
    So, one year ago? After more than 25 years without it? And a lot of people writing Java can't update to that.
    - jeberle 11mo ago
      Yeah, FFM adds many quality-of-life features - scoped lifetimes being a standout. If you just want an arena interface, ByteBuffer has been there since Java 1.4 (2002). It also does off-heap w/ ByteBuffer.allocateDirect(). https://docs.oracle.com/en/java/javase/25/docs/api/java.base/java/nio/ByteBuffer.html https://docs.oracle.com/en/java/javase/25/docs/api/java.base...
      - seanmcdirmid 11mo ago
        That brings back some memories...when Frank Yellin and Sheng Liang (from Javasoft) visited our team at UW I think in 1996 or 1997, we mentioned that our bytecode verifier/failure injector was really fast because we were using arena allocation, which was only possible (at the time) because we did the project in C. If you are using non-pointer offsets, you totally can do arena allocation with a byte buffer. I still don't get how you can do it safely with high level objects even with the mechanism described above, but there are definitely lots of unsafe ways to do it.

by Mawr 11mo ago

seanmcdirmid 11mo ago

Pretty hard to do arena allocation in Java without JVM primitive support.

jeberle 11mo ago
Not sure what you mean by "primitive support". Java 22 added FFM (Foreign Function & Memory). It works w/ both on-heap & off-heap memory. It has an Arena interface. https://openjdk.org/jeps/454 https://openjdk.org/jeps/454 https://docs.oracle.com/en/java/javase/25/docs/api/java.base/java/lang/foreign/Arena.html https://docs.oracle.com/en/java/javase/25/docs/api/java.base...
- Dylan16807 11mo ago
  So, one year ago? After more than 25 years without it? And a lot of people writing Java can't update to that.
  - jeberle 11mo ago
    Yeah, FFM adds many quality-of-life features - scoped lifetimes being a standout. If you just want an arena interface, ByteBuffer has been there since Java 1.4 (2002). It also does off-heap w/ ByteBuffer.allocateDirect(). https://docs.oracle.com/en/java/javase/25/docs/api/java.base/java/nio/ByteBuffer.html https://docs.oracle.com/en/java/javase/25/docs/api/java.base...
    - seanmcdirmid 11mo ago
      That brings back some memories...when Frank Yellin and Sheng Liang (from Javasoft) visited our team at UW I think in 1996 or 1997, we mentioned that our bytecode verifier/failure injector was really fast because we were using arena allocation, which was only possible (at the time) because we did the project in C. If you are using non-pointer offsets, you totally can do arena allocation with a byte buffer. I still don't get how you can do it safely with high level objects even with the mechanism described above, but there are definitely lots of unsafe ways to do it.