Handling Rust Arrays in Java

Rust Side

Arrays in Rust are fixed-size collections, and their size and layout must be precisely known for Java to interact with them effectively.

Example Rust Array:

#![allow(unused)]
fn main() {
#[no_mangle]
pub extern "C" fn create_array() -> *mut [i32; 5] {
    Box::into_raw(Box::new([1, 2, 3, 4, 5]))
}
}

Explanation: Box::into_raw creates a raw pointer, enabling Java to handle the array. Here, #[no_mangle] ensures the Rust function name remains unmangled, making it accessible from Java.

Java Side

To handle arrays from Rust in Java:

• Define a SequenceLayout for the array.
• Access elements via VarHandle.

SequenceLayout arrayLayout = MemoryLayout.sequenceLayout(5, ValueLayout.JAVA_INT);
VarHandle elementHandle = arrayLayout.elementVarHandle(ValueLayout.JAVA_INT);

Explanation:

SequenceLayout: This layout describes a fixed-size array (5 elements of i32).

VarHandle: Provides access to each element in the array.

Allocating and Accessing Elements

var arena = Arena.ofConfined();
MemorySegment arraySegment = arena.allocate(arrayLayout);

for (int i = 0; i < 5; i++) {
    int value = (int) elementHandle.get(arraySegment, (long) i);
    System.out.println("Array element " + i + ": " + value);
}

Explanation:

Memory Allocation: The array memory is managed within an arena, ensuring safety and easy cleanup.

Element Access: Each element is accessed via elementHandle, following Rust’s array layout.